Proceedings of Scotts Turfgrass Research Conference Volume 3—Weed Controls January 1972 First row, left to right: Jess Fults, George McVey, Andrew Powell, Clarence Seely, James Dewey, Harold Alley, John Jagschitz. Second row, left to right: P. C. Williams, Victor Youngner, Richard Schmidt, Eugene Arnold, Wayne Bingham, Arnold Appleby, Evert Burt, Granville Horn, Hayden Watkins, Vaughn Holyoke. Third row, left to right: Wayne Huffine, Clarence Watson, Richard Green, William Stottlemeyer, John Evans, Richard Post, Jack Butler, Delbert Hemphill, Lloyd Callahan, William Lewis, Clifford Porter, Harold Doellinger. Fourth and fifth rows, left to right: William Schwaderer, Clay Switzer, Coleman Ward, Donald Kaufman, Charles Long, William Kneebone, Donald Gruenbaum, Raymond Dickens, John Ahrens, Robert Newman, William Scheer, Wallace Menn, Robert Miller, William Young, Frederick Lede- boer, E. P. Sylwester, Donald White, A1 Turgeon, William Daniel. Proceedings of Scotts Turfgrass Research Conference Volume 3 — Weed Controls January 1972 EDITORS Richard E. Schmidt, Chief Editor Department of Agronomy Virginia Polytechnic Institute and State University Blacksburg, Virginia 24061 Jack D. Butler Department of Horticulture University of Illinois Urbana, Illinois 61801 Delbert D. Hemphill Department of Horticulture University of Missouri Columbia, Missouri 65201 Richard T. Bangs William L. Schwaderer O. M. Scott & Sons Company Marysville, Ohio 43040 O. M. Scott & Sons Company • PUBLISHER A Subsidiary of ITT Marysville, Ohio 43040 Proceedings of Scotts Turfgrass Research Conference Volume 3 — Weed Controls Copyright © 1972 by the O. M. Scott & Sons Company. Printed in the United States of America. Library of Congress Catalog Card Number; 75-180289 P R E F A CE T h is v o l u me c o n t a i ns the P r o c e e d i n gs of S c o t ts T u r f g r a ss R e s e a r ch C o n f e r e n ce on W e ed C o n t r o l s. R e p r e s e n t a t i v es at the c o n f e r e n ce i n c l u d ed 42 r e s e a r c h e rs f r om 38 s t a t es and C a n a d a, j o i n ed by S c o t t 's r e s e a r ch s t a f f. T he c o n f e r e n ce w as h e ld at the O. M. S c o tt & Sons C o m p a n y, M a r y s v i l l e, Ohio, on J u ly 2 7 - 2 8, 1970. T en f o r m al p a p e rs w e re p r e s e n t ed on v a r i o us a s p e c ts of w e ed c o n t r ol - t h e ir u s e s, e f f e c ts and c u r r e nt r e c o m m e n d a- t i o n s. A q u e s t i on and a n s w er p e r i od f o l l o w ed m a ny of the p r e- s e n t a t i o n s. A ll of the p a p e rs p r e s e n t ed at the c o n f e r e n c e, as w e ll as the t r a n s c r i p ts of the d i s c u s s i o n s, a re i n c l u d ed in this v o l u m e. T h is unique e n d e a v or p r o v i d ed r a p p o rt b e t w e en turf w e ed c o n t r ol s p e c i a l i s t s, r e s u l t i ng in h i g h ly r e w a r d i ng d i s c u s s i o n s. W i t h in t h e se p r o c e e d i n gs a re p a p e rs and r e f e r e n c es that a re c o n s i d e r ed as i n v a l u a b le a i ds to r e s e a r c h e r s, as w e ll as s t u- d e n ts w o r k i ng with t u r f g r a ss h e r b i c i d e s. O. M. S c o tt & Sons c e r t a i n ly is to be a p p l a u d ed f or taking the l e a d e r s h ip in s p o n- s o r i ng a g e n u i n e ly s t i m u l a t i n g, e d u c a t i o n al p r o j e ct as this t r u ly w a s. T he p a p e rs in t h is P r o c e e d i n gs m ay be r e p r i n t ed in w h o le or in p a rt - s u b j e ct to a c c u r a te quoting with p r o p er c r e d it to the a u t h o rs and O. M. S c o tt & S o n s. T he e d i t o rs and S c o t ts would l i ke to a c k n o w l e d ge the c o o p- e r a t i on of the a u t h o rs and c o n f e r e n ce p a r t i c i p a n ts ing this P r o c e e d i n g s. in p r e p a r- R i c h a rd E. S c h m i dt C h i ef E d i t or C O N T E N TS P r e f a ce P a r t i c i p a n ts E c o l o g i c al F o r c es A f f e c t i ng W e e ds and T h e ir C o n t r ol V I C T OR B. Y O U N G N ER i ii 1 T he N a t u re of B i o c h e m i c al M e c h a n i sm of H e r b i c i de S e l e c t i v i ty S. W A Y NE B I N G H AM . 27 E f f e c ts of H e r b i c i d es on P l a nt P h y s i o l o g i c al P r o c e s s es D O N A LD E. D A V IS U n i q ue A p p r o a c h es to W e ed C o n t r ol W I L L I AM S T O T T L E M Y ER and R I C H A RD B A I L EY P e r s i s t e n ce and D e g r a d a t i on of C o m m o n ly U s ed T u rf H e r b i c i d es D O N A LD D. K A U F M AN in O ur E n v i r o n m e nt P r a c t i c al T o x i c o l o gy in C o n s u m er U se of T u r f g r a ss H e r b i c i d es J A M ES E. D E W EY S p e c i al D i s c u s s i on P e r i od M i d w e st C u r r e nt T r e n ds in T u r f g r a ss W e ed C o n t r ol W I L L I AM H. D A N I EL N o r t h e rn C u r r e nt T r e n ds in T u r f g r a ss W e ed C o n t r ol C L AY M. S W I T Z ER W e s t e rn C u r r e nt T r e n ds in T u r f g r a ss W e ed C o n t r ol W A Y NE H U F F I NE S o u t h e rn C u r r e nt T r e n ds in T u r f g r a ss W e ed C o n t r ol E V E RT O. B U RT 49 75 93 133 149 155 161 167 171 P A R T I C I P A N TS John F. A h r e ns T he C o n n e c t i c ut A g r i c u l t u r al E x p e r i m e nt Station V a l l ey L a b o r a t o ry W i n d s o r, C o n n e c t i c ut 06095 H a r o ld P. A l l ey D i v i s i on of P l a nt S c i e n ce U n i v e r s i ty of W y o m i ng L a r a m i e, W y o m i ng 82070- A r n o ld P. A p p l e by D e p a r t m e nt of S o i ls and C r o ps R u t g e rs - T he State U n i v e r s i ty N ew B r u n s w i c k, N ew J e r s ey 08903 W. E u g e ne A r n o ld D e p a r t m e nt of P l a nt S c i e n ce South D a k o ta State U n i v e r s i ty B r o o k i n g s, South D a k o ta 57006 D i ck B a n gs G o v e r n m e n t - I n d u s t ry R e l a t i o ns O. M. S c o tt & Sons C o m p a ny M a r y s v i l l e, Ohio 43040 S. W a y ne B i n g h am D e p a r t m e nt of P l a nt P a t h o l o gy and P h y s i o l o gy V i r g i n ia P o l y t e c h n ic Institute and State U n i v e r s i ty B l a c k s b u r g, V i r g i n ia 24061 E v e rt O. B u rt U n i v e r s i ty of F l o r i da P l a n t a t i on F i e ld L a b o r a t o ry F o rt L a u d e r d a l e, F l o r i da 3 3 3 14 J a ck D. B u t l er D e p a r t m e nt of H o r t i c u l t u re U n i v e r s i ty of I l l i n o is U r b a n a, I l l i n o is 61801 L l o yd M. C a l l a h an D e p a r t m e nt of A g r o n o my U n i v e r s i ty of T e n n e s s ee K n o x v i l l e, T e n n e s s ee 37901 W i l l i am H. D a n i el D e p a r t m e nt of A g r o n o my P u r d ue U n i v e r s i ty L a f a y e t t e, Indiana 47907 J a m es E. D e w ey D e p a r t m e nt of E n t o m o l o gy C o r n e ll U n i v e r s i ty I t h a c a, N ew Y o rk 14850 R a y m o nd D i c k e ns D e p a r t m e nt of A g r o n o my and S o i ls A u b u rn U n i v e r s i ty A u b u r n, A l a b a ma 36830 J o hn O. E v a ns D e p a r t m e nt of P l a nt S c i e n ce U t ah State U n i v e r s i ty L o g a n, Utah 84321 J e ss L. F u l ts D e p a r t m e nt of B o t a ny and P l a nt P a t h o l o gy C o l o r a do State U n i v e r s i ty F o rt C o l l i n s, C o l o r a do 80521 D a v id G r e en P r o d u ct D e v e l o p m e nt O. M. S c o tt & Sons C o m p a ny M a r y s v i l l e, Ohio 43040 R i c h a rd G r e en D e p a r t m e nt of A g r o n o my and S o il S c i e n ce U n i v e r s i ty of H a w a ii H o n o l u l u, H a w a ii 96822 D e l b e rt D. H e m p h i ll D e p a r t m e nt of H o r t i c u l t u re U n i v e r s i ty of M i s s o u ri C o l u m b i a, M i s s o u ri 65201 V a u g hn H. H o l y o ke D e p a r t m e nt of P l a nt and S o il S c i e n c es U n i v e r s i ty of M a i ne O r o n o, M a i ne 04473 G r a n v i l le C. H o rn D e p a r t m e nt of O r n a m e n t al H o r t i c u l t u re U n i v e r s i ty of F l o r i da G a i n e s v i l l e, F l o r i da 32601 W a y ne H u f f i ne D e p a r t m e nt of A g r o n o my O k l a h o ma State U n i v e r s i ty S t i l l w a t e r, O k l a h o ma 74074 J o hn A. J a g s c h i tz D e p a r t m e nt of A g r o n o my U n i v e r s i ty of Rhode I s l a nd K i n g s t o n, R h o de I s l a nd 02881 D o n a ld D. K a u f m an A g r i c u l t u r al R e s e a r ch S e r v i ce U SD A B e l t s v i l l e, M a r y l a nd 20705 W i l l i am R. K n e e b o ne D e p a r t m e nt of A g r o n o my U n i v e r s i ty of A r i z o na T u c s o n, A r i z o na 85721 F r e d r i ck B. L e d e b o er D e p a r t m e nt of H o r t i c u l t u re C l e m s on U n i v e r s i ty C l e m s o n, South C a r o l i na 29631 W i l l i am M. L e w is D e p a r t m e nt of C r op S c i e n ce N o r th C a r o l i na State University- R a l e i g h, N o r th C a r o l i na 27607 C h a r l es E. L o ng D e p a r t m e nt of H o r t i c u l t u re K a n s as State University- M a n h a t t a n, K a n s as 66502 R o b e rt W. M i l l er D e p a r t m e nt of A g r o n o my T he Ohio State U n i v e r s i ty C o l u m b u s, Ohio 43210 W a l l a ce G. Menn D e p a r t m e nt of S o il and C r op S c i e n c es T e x as A & M U n i v e r s i ty C o l l e ge Station, T e x as 77843 R o b e rt C. N e w m an D e p a r t m e nt of H o r t i c u l t u re U n i v e r s i ty of W i s c o n s in M a d i s o n, W i s c o n s in 52706 C l i f f o rd D. P o r t er D e p a r t m e nt of A g r o n o my and G e n e t i cs W e st V i r g i n ia State U n i v e r s i ty M o r g a n t o w n, W e st V i r g i n ia 26506 R i c h a rd L. P o st D e p a r t m e nt of P l a n t, S o il and W a t er S c i e n c es U n i v e r s i ty of N e v a da R e n o, N e v a da 89507 A n d r ew J. P o w e ll D e p a r t m e nt of A g r o n o my U n i v e r s i ty of M a r y l a nd C o l l e ge P a r k, M a r y l a nd 20742 W i l l i am S c h e er W a s h i n g t on C o o p e r a t i ve E x t e n s i on S e r v i ce K i ng C o u n ty A r ea O f f i ce S e a t t l e, W a s h i n g t on 98109 R i c h a rd E. S c h m i dt D e p a r t m e nt of A g r o n o my V i r g i n ia P o l y t e c h n ic Institute and State U n i v e r s i ty B l a c k s b u r g, V i r g i n ia 24061 C l a r e n ce I. S e e ly D e p a r t m e nt of P l a nt S c i e n ce U n i v e r s i ty of Idaho M o s c o w, Idaho 83843 J im S i m m o n s, D i r e c t or P r o d u ct D e v e l o p m e nt O. M. S c o tt & Sons C o m p a ny M a r y s v i l l e, Ohio 43040 W i l l i am S t o t t l e m y er B i o - C h e m i c al R e s e a r ch O. M. S c o tt & S o ns C o m p a ny M a r y s v i l l e, Ohio 43040 C l ay M. S w i t z e r, C h a i r m an D e p a r t m e nt of B o t a ny U n i v e r s i ty of G u e l ph G u e l p h, O n t a r i o, C a n a da E r h a r dt P. S y l w e s t er D e p a r t m e nt of B o t a ny and P l a nt P a t h o l o gy I o wa State U n i v e r s i ty A m e s, Iowa 50010 J e r ry T i m m o ns C h e m i c al R e s e a r ch O. M. S c o tt & Sons C o m p a ny M a r y s v i l l e, Ohio 43040 Al T u r g e on D e p a r t m e nt of C r op and S o il S c i e n c es M i c h i g an State University- E a st L a n s i n g, M i c h i g an 48823 C o l e m an Y. W a rd D e p a r t m e nt of Agronomy- M i s s i s s i p pi State University- S t a te C o l l e g e, M i s s i s s i p pi 39762 H a y d en W a t k i ns D e p a r t m e nt of A g r o n o my U n i v e r s i ty of K e n t u c ky L e x i n g t o n, K e n t u c ky 40506 C l a r e n ce E. W a t s on D e p a r t m e nt of A g r o n o my N ew M e x i co State U n i v e r s i ty L as C r u c e s, N ew M e x i co 88001 D o n a ld B. White D e p a r t m e nt of H o r t i c u l t u re S c i e n ce U n i v e r s i ty of M i n n e s o ta St. P a u l, M i n n e s o ta 55101 W i l l i am A. Young D e p a r t m e nt of H o r t i c u l t u re L o u i s i a na State U n i v e r s i ty B a t on R o u g e, L o u i s i a na 70803 V i c t or B. Y o u n g n er D e p a r t m e nt of A g r o n o my U n i v e r s i ty of C a l i f o r n ia R i v e r s i d e, C a l i f o r n ia 92502 E C O L O G I C AL F O R C ES A F F E C T I NG W E E DS A ND T H E IR C O N T R OL V i c t or B. Y o u n g n er D e p a r t m e nt of Agronomy- U n i v e r s i ty of C a l i f o r n ia R i v e r s i d e, C a l i f o r n ia 92502 I n t r o d u c t i on A c o m p l e te d i s c u s s i on of the e c o l o gy of w e e ds would e n- c o m p a ss a ll a s p e c ts of plant e c o l o g y. T h e re is l i t t le that is u n i q ue about w e e ds in this r e s p e c t, and m o st of the g e n e r al T h e r e f o r e, c o n c e p ts and p r i n c i p l es of e c o l o gy a p p ly to t h e m. a r e v i ew of s o me of t h e se c o n c e p ts with s p e c i f ic r e f e r e n ce to w e e ds of t u rf p r o v i d es a n e c e s s a ry b a c k g r o u nd f or s a fe and e f f i c i e nt w e ed c o n t r o l. T he e c o l o g i c al f a c t o rs r e l a t ed to w e ed e s t a b l i s h m e nt and g r o w th m ay be d i v i d ed into the n a t u r al f a c t o rs and the m a n - d e- t e r m i n ed or m a n - m o d i f i ed f a c t o r s - - t h o se of t u rf c u l t u re and m a n a g e m e n t. M a n, of c o u r s e, m o d i f i es m o st of the e n v i r o n- m e n t al f a c t o rs to s o me d e g r ee but c e r t a in f a c t o rs a re r e g u l a t ed to a m u ch g r e a t er extent than o t h e r s. Outdoor a ir is a f a c t or that m an c an m o d i fy only s l i g h t l y, but d e f o l i a t i on (mowing) is a f a c t or that is a l m o st e n t i r e ly m an m a d e. t e m p e r a t u re F r om the v i e w p o i nt of w e ed c o n t r o l, e c o l o g i c al f a c t o rs m ay be c o n s i d e r ed as t h ey r e l a te d i r e c t ly to the t u rf and w e ed plant or as t h ey a f f e ct a b s o r p t i on and a c t i v i ty of h e r b i c i d e s. T h is d i s c u s s i on w i ll be c o n f i n ed l a r g e ly to the f i r st a s p e ct and to the m o d i f i c a t i on of t h e se f a c t o rs as a m e a ns of w e ed c o n- t r o l. I n t e r r e l a t ed E c o l o g i c al F a c t o rs M a ny of the e n v i r o n m e nt f a c t o rs of g r e a t e st i m p o r t a n ce to t u rf c u l t u re a re t h o se of a m i c r o - e n v i r o n m e nt extending f r om 2 -4 i n c h es a b o ve to 2 -4 i n c h es b e l ow the s o il s u r f a c e. T he n a- t u re of t h is m i c r o - e n v i r o n m e nt t u r al p r a c t i c es and u t i l i z a t i o n. is l a r g e ly d e t e r m i n ed by t u rf c u l- Good ( 1931, 1953) s t a t ed that d i s t r i b u t i on of a s p e c i es or b i o t y pe w as c o n t r o l l ed p r i m a r i ly by the d i s t r i b u t i on of c l i m a t ic f a c t o rs and, s e c o n d a r i l y, by the d i s t r i b u t i on of e d a p h ic f a c t o r s. T he s i g n i f i c a n ce of the c o n c e pt is d e m o n s t r a t ed by w e e ds s u ch as c r a b g r a s s, D i g i t a r is s a n g u i n a l i s, w h i ch m ay be found w h e r- e v er t e m p e r a t u r e, the c l i m a t ic f a c t o r, is s a t i s f a c t o r y. H o w e v e r, l e a st s o il m o i s t u r e, a f a c t or w h i ch c an be r e g u l a t ed by m an at to s o me d e g r e e, d e t e r m i n es i ts d i s t r i b u t i on in any s i n g le t u rf a r e a. R e l a t ed to G o o d 's t h e o ry of plant d i s t r i b u t i on a re the l a ws of t o l e r a n ce p r o p o s ed by S h e l f o rd ( 19 13), Good ( 1931) and M a s on ( 19 36). P l a n ts with w i de r a n g es of t o l e r a n ce f or m a ny f a c t o rs of the e n v i r o n m e nt w i ll be w i d e ly d i s t r i b u t e d. T o l e r a n c es h a ve is a g e n e t ic b a se and the r a n ge of t o l e r a n ce of a t a x o n o m ic unit the s um of the r a n g es of its m e m b er b i o t y p e s. H o w e v e r, t h e re a re t i m es in the l i fe c y c le of a plant w h en it m ay h a ve a l ow t o l e r a n ce to c e r t a in s p e c i f ic f a c t o r s. P oa annua p r o v i d es an e x c e l l e nt i l l u s t r a t i on of t h e se c o n- It is a h i g h ly v a r i a b le s p e c i es with w i de r a n g es of t o l- c e p t s. e r a n ce f or m a ny f a c t o r s. B e c a u se of t h i s, it is w i d e ly d i s t r i b u t ed of a ll p l a n t s, l i v i ng and r e p r o d u c i ng in m a ny d i f f e r e nt e n v i r o n m e n t s. H o w e v e r, as Hovin ( 1958b) h as shown, m o d e r a t e ly high night t e m p e r a t u r es d u r i ng i n f l o r e s c e n ce d e- v e l o p m e nt w i ll r e s u lt in p o l l en s t e r i l i t y; t h u s, l e v el of t o l e r a n ce f or high t e m p e r a t u re at t h is c r i t i c al s t a ge of i ts l i fe c y c l e. one of the m o st t h e re is a l o w er A t h i rd c o n c e p t, s o m e w h at s i m i l ar to t h o se j u st d e s c r i b e d, is T a y l o r!s ( 1934) t h e o ry of l i m i t i ng f a c t o r s. B a s ed on L i e b i g 's , !l aw of the m i n i m u m ," t h is t h e o ry s t a t es that g r o w th and s u r- in v i v al of a plant is dependent upon the e n v i r o n m e n t al f a c t or l i fe l e a st s u p p l y, or l e a st f a v o r a b le at any s p e c i f ic s t a ge in its c y c l e. S o il m o i s t u re at t i me of s e ed g e r m i n a t i on is a l i m i t i ng f a c t or f or c r a b g r a ss and m a ny o t h er p l a n t s. L i g ht f or s e e d l i ng d e v e l o p m e nt ( d i s c u s s ed in m o re d e t a il l a t e r) m ay o f t en be a l i m i t i ng f a c t or f or P oa annua. M o d e rn w e ed c o n t r ol p r a c t i c es r e c o g n i ze t h is p r i n c i p l e, u s i ng k n o w l e d ge of c r i t i c al s t a g es in l i fe c y c l es f or the m o st a d v a n t a g e o us t i m i ng of c u l t u r al and c h e m i c al c o n t r ol m e t h o d s. R e p l a c e a b i l i ty of one e c o l o g i c al f a c t or by a n o t h er (an i m- is g e n e r a l ly i l l u s t r a t ed by the c l a s- p o r t a nt e c o l o g i c al p r i n c i p l e) s ic e x a m p le of s u b s t i t u t i on of altitude f or l a t i t u d e. s i d e, C a l i f o r n i a, w i th an altitude b e l ow 1000 f t ., the c l i m a te is s u b t r o p i c al and w a rm s e a s on t u r f g r a s s es a re d o m i n a n t. M a ny t e m p e r a te c l i m a te w e e ds a re a b s e nt or abundant in w i n t er only. T w e n t y - f i ve m i l es a w ay in the A r r o w h e ad r e g i on at e l e v a t i o ns a r o u nd 5000 ft. a t e m p e r a te c l i m a te e x i s t s, w a rm s e a s on g r a s- s es a re a b s e nt and m a ny w e e ds found in the m o re n o r t h e rn r e g- i o ns a re c o m m o n. In R i v e r- M a n, t h r o u gh i r r i g a t i on p r a c t i c e s, h as m a de a f a c t or s u b- f r om stitution of no l e ss i m p o r t a n c e. He h as s u b s t i t u t ed w a t er s t r e a m s, s o u t h w e s t. As a r e s u l t, l u sh g r a ss and e x o t ic w e e ds g r ow a r e as w h i ch w o u ld o t h e r w i se s u p p o rt only the h a r d i e st of x e r o- p h y t ic p l a n t s. l a k es and w e l ls f or the d e f i c i e nt r a i n f a ll of the a r id in In m o st plant c o m m u n i t i e s, c o m p e t i t i on o c c u rs f or the e n- v i r o n m e n t al f a c t o rs in l i m i t ed s u p p ly or a v a i l a b i l i t y. C o m p e t i- t i on m ay e x i st a m o ng p a r ts of a s i n g le plant, a m o ng p l a n ts of the s a me s p e c i es or a m o ng p l a n ts of d i f f e r e nt s p e c i e s. C o m- p e t i t i on a m o ng p l a n ts is the u l t i m a te c o n c e rn of w e ed s c i e n c e. By c u l t u r al and c h e m i c al m e t h o d s, we s t r i ve to g i ve c r o p s, p l a n ts or t u r f g r a s s es a c o m p e t i t i ve a d v a n t a ge o v er the unwanted s p e c i e s. T h r o u gh c o m p e t i t i on and n a t u r al s e l e c t i on of i n d i v i d u a ls b e st a b le to s u r v i ve and r e p r o d u c e, m o d e rn p l a n ts h a ve e v o l v ed and h a ve a c q u i r ed adaptation to s p e c i f ic e n v i r o n m e n t al c o n d i- t i o n s. E v o l u t i o n, of c o u r s e, is a d y n a m ic p r o c e ss t o d ay as w e ll as in the p a s t. T u rf c u l t u r e, a r e l a t i v e ly r e c e nt d e v e l o p m e n t, is e x e r t i ng n ew s e l e c t i on p r e s s u r es on both g r a s s es and w e e d s. B e t t er adapted t u r f g r a s s es and m o re c o m p e t i t i ve w e e ds u n d er s p e c i f ic t u rf c o n d i t i o ns a re e v o l v i n g. S u p e r i or t u rf e c o t y p es h a ve b e en r e c o g n i z ed in both the g r a s s es u s ed f or t h is p u r p o se and the w e e ds invading v a r i o us t y p es of t u r f s. A l t h o u gh students of e c o l o gy f r e q u e n t ly r e f er to the e f f e c ts of a s i n g le e n v i r o n m e n t al f a c t or on an o r g a n i s m, it is g e n e r a l ly r e c o g n i z ed that a ll f a c t o rs a f f e ct a plant m o re or l e ss s i m u l t- a n e o u s ly and i n t e r a ct to m o d i fy e a ch o t h e r. C a in (1944) r e f e r- r ed to t h is as the h o l o c o e n o t ic e n v i r o n m e nt and s t r e s s ed the i m p o r t a n ce of the c o n c e pt to u n d e r s t a n d i ng plant r e s p o n s e s. A g r e at s i m p l i f i c a t i on of B i l l i n g s1 (1952) d i a g r am i l l u s t r a t i ng the h o l o c o e n o t ic e n v i r o n m e nt is shown in F i g. 1. Figure 1. A s i m p l i f i ed v e r s i on of B i l l i n g s1 of the holocoenotic environment. (1953) i l l u s t r a t i on R e f e r e n ce to s p e c i f ic s t u d i es and o b s e r v a t i o ns w i ll i l l u s- t r a te the a f o r e m e n t i o n ed p r i n c i p l es and r e l a te t h em m o re d i- r e c t ly to t u r f g r a ss w e ed c o n t r o l. Figure 2. Ecotypes of Poa annua. Comparison of an upright open growing f i e ld type ( l e f t) with a dwarf compact dark green p u t t i ng green type ( r i g h t ). Figure 3. Ecotypes of Poa annua. Comparison of a normal heavy- f l o w e r i ng fairway type ( l e f t) with a dwarf creeping non- f l o w e r i ng p u t t i ng green type ( r i g h t ). P oa annua f u r n i s h es one of the b e st e x a m p l es of e c o t y pe s e l e c t i on u n d er turf c o n d i t i o ns (Hovin, 1958a; Y o u n g n e r, 1959). A p r i m a ry s e l e c t i on f o r ce is the h e i g ht and f r e q u e n cy of m o w- i n g. D i s t i n ct t y p es h a ve b e en s e l e c t ed f r om golf g r e e n s, f a i r- w a ys and open f i e l ds ( F i g. 2, 3). F i e ld t y p e s, the t y p i c al P oa a n n u a, a re c l e a r ly annual, u p r i g h t, bunchy and p r o l i f ic s e ed p r o d u c e r s. P u t t i ng g r e en t y p e s, to the o t h er e x t r e m e, a re p e r- e n n i a l, p r o s t r a t e, s p r e a d i ng and o f t en a l m o st s t o l o n i f e r o u s. T h ey a re o f t en shy s e ed p r o d u c e rs and m ay e v en be s t e r i l e. T h e se c h a r a c t e r i s t i cs a re u n i q u e ly a d v a n t a g e o us u n d er the put- ting g r e en e n v i r o n m e n t, but w o u ld be d e l e t e r i o us u n d er f i e ld c o n d i t i o n s. l e ss v i g o r o us c u l t u r al r e q u i r e m e nt of f a i r w a ys and g e n e r al t u r f. T he e x i s t e n ce of p e r e n n i a l, s t e r i l e, or n e a r ly s t e r i le e c o t y p es on putting g r e e ns r e d u c es the e f f e c t i v e n e ss of p r e - e m e r g e n ce c h e m i c al c o n t r ol p r a c t i c e s. I n t e r m e d i a te t y p es m ay be found u n d er the M o i s t u re F a c t o rs S o il m o i s t u r e, e i t h er e x c e s s i ve or d e f i c i e n t, m ay f a v or e s t a b l i s h m e nt and c o m p e t i t i on of w e e ds with t u r f g r a s s e s. W e ed s p e c i es in the t wo m o i s t u re c o n d i t i o ns w i ll be d i f f e r e n t, h o w- e v e r, as i l l u s t r a t ed by o b s e r v a t i o ns m a de in b e r m u d a g r a ss i r r i g a t ed by a p o o r ly d e s i g n ed and m a i n t a i n ed s y s t em u n p u b l i s h e d ). T a b le 1 l i s ts w e e ds found in the e x c e s s i v e ly w et a r e as a r o u nd s p r i n k l er h e a ds and in d ry a r e as w h e re s p r i n k l er c o v e r a ge w as p o o r. A n n u al and m o i s t u re l o v i ng w e e ds d o m i- n a t ed the w et a r e as a l m o st to the e x c l u s i on of the b e r m u d a- g r a s s. T he a r e as of good s o il m o i s t u re c o n d i t i o ns w e re a l- m o st p u re b e r m u d a g r a s s, but w h e re s p r i n k l er c o v e r a ge w as p o o r, s p e c i es m o re t o l e r a nt of l ow s o il m o i s t u re d o m i n a t e d. turf ( Y o u n g n e r, T a b le 2 i l l u s t r a t es the e f f e c ts of s o il m o i s t u re l e v e ls on the s u r v i al of P oa annua in b e r m u d a g r a ss t u rf ( Y o u n g n e r, L ow s o il m o i s t u re p l o ts r e c e i v ed t h r e e - f o u r t hs of an inch of w a t er e v e ry ten d a ys and the h i gh s o il m o i s t u re p l o ts r e c e i v ed o n e - h a lf i n ch of w a t er e v e ry t h r ee d a y s. A l t h o u gh P oa annua p o p u l a t i o ns w e re the s a me in both i r r i g a t i on t r e a t m e n ts s p r i n g, by m i d - s u m m er no P oa annua r e m a i n ed in the d ry t r e a t m e n t. P o p u l a t i on r e d u c t i on d u r i ng the s a me t i me w as only s l i g ht in the w et t r e a t m e n t. in the 1959). T a b le 1. W e e ds found in w e t, m o i st and d ry a r e as in a b e r m u d a- g r a ss t u r f. E x c es s i v e ly wet (Abundant) C r a b g r a ss O x a l is Spotted S p u r ge A n n u al B l u e g r a ss B e n t g r a ss M o d e r a te m o i s t u re F ew or no w e e ds D ry B ur C l o v er B l a ck M e d ic D r op S e ed T a b le 2. P o p u l a t i o ns of P oa annua and C y n o d on d a c t y l on at two l e v e ls of s o il m o i s t u r e. ( L ow m o i s t u r e) M e an n u m b er of plants p er s a m p le P e r c e nt p r e s e n ce P o p u l a t i on e s t i m a t e s - M ay P oa annua C y n o d on d a c t y l on 10-20+1-01 4-80+0-79 100*00 100-00 P o p u l a t i on e s t i m a t e s - J u ly P oa annua C y n o d on d a c t y l on P o p u l a t i on e s t i m a t e s - M ay P oa annua C y n o d on d a c t y l on P o p u l a t i on e s t i m a t e s - J u ly P oa annua C y n o d on d a c t y l on 0-00 14-82+1-05 100-00 (High m o i s t u r e) 10-51 + 0-98 4-09+ -67 100-00 98-36 8-82 + 0-88 6-38 + 0-51 92-10 100-00 L i g ht F a c t o rs C o m p e t i t i on f or light o c c u rs within m o st t u r fs and o t h er g r a s s l a n ds w h en f u l ly e s t a b l i s h e d. As D o n a ld (1963) pointed out, c o m p e t i t i on f or s p a ce r a r e ly e x i s ts and that w h i ch is o f t en r e f e r r ed to as s u ch is a c t u a l ly c o m p e t i t i on f or light. M o re and m o re of the i n c i d e nt light is i n t e r c e p t ed by the l e a v es as the turf i n c r e a s es in h e i g ht and d e n s i t y. When l e af d e n s i ty is s u ch that e s s e n t i a l ly a ll light is i n t e r c e p t ed but a ll l e a v es r e c e i ve a d e q u a te l i g h t, the o p t i m um l e af a r ea index (the r a t io of l e af s u r f a ce to s o il s u r f a c e) and the m a x i m um g r o w th r a te a re r e a c h e d. E v e n t u a l l y, s e v e re c o m p e t i t i on f or light d e- v e l o ps a m o ng the l e a v e s. As d e n s i ty of the l e af c a n o py c r e a s e s, o l d er l o w er l e a v es r e c e i ve i n s u f f i c i e nt light and e v e n- t u a l ly d i e. old l e a v es e q u a ls the r a te of e m e r g e n ce of n ew In t i m e, the death r a te of l e a v e s. i n- A v i g o r o us d e n se t u rf is n e c e s s a ry to p r e v e nt w e ed i n v a- sion. T h is can, in p a r t, be a c h i e v ed by a m o w i ng h e i g ht and f r e- q u e n cy that m a i n t a i ns the l e af a r ea i n d ex as n e ar the o p t i m um as o t h er r e q u i r e m e n ts of the t u rf p e r m i t. T he r e s u l t i ng high n et a s s i m i l a t i on r a te would p e r m it good t i l l er and root d e v e l- o p m e n t. B r o u g h am (1957) h as i l l u s t r a t ed in F i g. 4 the i m p o r- t a n ce of cutting h e i g ht to the t i me r e q u i r ed b e f o re the o p t i m um l e af a r ea i n d ex (95% light i n t e r c e p t i o n) c o u r s e, it is e q u a l ly i m p o r t a nt to m a i n t a in a cutting f r e q u e n cy that w i ll p r e v e nt l o w er l e a v es f r om y e l l o w i n g, due to i n s u f f i c- i e nt is a g a in r e a c h e d. Of light. C l i p p i ng height h as b e en shown to l o w er t i l l e r i ng r a t e s, if l e af t i s s ue only is cut. H o w e v e r, if g r o w i ng points a re r e m o v e d, t i l l e r i ng w i ll be s t i m u l a t ed by the d e s t r u c t i on of a p i c al d o m i- n a n ce ( M a i da and E h a r a, 1962; J a m i s on and H u s s, 1959). T h u s, in t u r fj c l o se m o w i ng of s t o l o n i f e r o us g r a s s es w h e re g r o w i ng p o i n ts w o u ld be r e m o v ed m i g ht e n c o u r a ge turf d e n s i t y, but w o u ld h a ve the o p p o s i te e f f e ct on n o n s t o l o n i f e r o us s p e c i e s, such as b l u e g r a s s. C l i p p i ng i n c r e a s es the f l o w e r i ng of K i k u y u g r a ss as w e ll as i n c r e a s i ng its d e n s i ty ( Y o u n g n e r, 1961b). A n o t h er e f f e ct of c l i p p i ng on c o m p e t i t i on f or light m ay be s e en with P oa annua e s t a b l i s h m e nt in t u rf ( Y o u n g n e r, 1959). Figure 4. E f f e c ts of c u t t i ng height of a mixed sward onetime index (95%) required to reach optimum l e af area l i g ht i n t e r c e p t i o n. a line b e t w e en the P o p u l a t i on c o u n ts m a de a l o ng e a ch side of h i gh cut r o u g hs and l ow cut f a i r w a ys of t en s o u t h e rn C a l i f o r n ia g o lf c o u r s es s h o w ed that l o w er clipping w as f a v o r a b le to P oa annua e s t a b l i s h m e nt ( T a b le 3). R e m o v al of m o re b e r m u d a- g r a ss l e af w as thought to p e r m it m o re l i g ht to r e a ch the P oa annua s e e d l i n gs d u r i ng the f a ll g e r m i n a t i on p e r i o d. A s i m i- l ar e f f e ct w as d e m o n s t r a t ed f or v e r t i c al m o w i ng or r e n o v a- t i on in the f a ll ( Y o u n g n e r, 1959, 1968; Y o u n g n er and N u d g e, 1968a). P oa annua p o p u l a t i o ns w e re i n c r e a s ed by t h is p r a c t i ce on both b e n t g r a ss g r e e ns and b e r m u d a g r a ss l a w n s. T e m p e r a t u re F a c t o rs T e m p e r a t u re a l so h as v a r i o us e f f e c ts on p l a n ts of g r e at s i g n i f i c a n ce to w e ed c o n t r ol in t u r f. F l o w e r i ng of m a ny s p e- c i es is h i g h ly t e m p e r a t u re s e n s i t i v e. T he p r e v i o u s ly c i t ed high t e m p e r a t u re induced p o l l en a b o r t i on (Hovin, 1958b) of P oa T a b le 3. D e n s i t i es of P oa annua p o p u l a t i o ns in l ow and h i g h- cut t u r f. D e n s i ty as m e an n u m b er of p l a n ts p er 1 l /2 " Plug L ow H i gh L o c a t i on D i f f e r e n ce 1 2 3 4 5 6 7 8 9 10 T o t al M e an 32-29 15-42 60-33 6-54 1 1 - 42 32-63 66-37 33-67 47-88 62-54 369-09 36-91 C a l c u l a t ed t 9-88 0-00 2 - 13 0-29 0-21 1 - 58 0-63 1-33 8-92 2-25 27-22 2-72 22-41 15-42 58*20 6-25 1 1 - 21 31-05 65-74 32-34 38-96 60-29 341-87 34-19 5-07 3-25 t at 0-01 point, 9 D . F. = D i f f e r e n ce is s i g n i f i c a nt at 1% l e v el T a b le 4. A p p e a r a n ce of f l o r e t s, a f t er 4 w e e ks of t r e a t m e n t, f e r t i le P. c l a n d e s t i n u m. in D ay l e n g th S t a m e ns (hr) 8 16 24 8 16 24 T e m p e r a t u re 2 7 °C E x s e r t ed E x s e r t ed E x s e r t ed T e m p e r a t u re 1 0 °C N o n e x s e r t ed N o n e x s e r t ed N o n e x s e r t ed T e m p e r a t u re 2 1 °C (day) to 1 0 °C (night) 8 16 E x s e r t ed E x s e r t ed F e r t i le p o l l en (%) 89 + 16 65 + 11 71 + 13 5 36 ± 21 + 6 0.4 ± 0.2 72 + 13 82 + 16 In K i k u y u g r a s s, annua is p e r h a ps c h a r a c t e r i s t ic of m a ny w e e d s. P e n n i s e t um c l a n d e s t i n u m, m a le s t e r i l i ty h as b e en shown to be the r e s u lt of l ow t e m p e r a t u re ( Y o u n g n e r, 1961b). In s u m m e r, the f e r t i le s t r a in w h en g r o w i ng in t u rf is c o v e r ed with p e r f e ct f l o w e rs ( F i g. 5). D u r i ng the c o ol w e a t h er of f a ll and w i n t e r, a n t h e rs a b o rt and o n ly the s t i g m as a re e x s e r t e d. G r o w th c h a m- b er s t u d i es s h o w ed t h is to r e s u lt f r om t e m p e r a t u r es of 1 0 °C or b e l ow as shown in T a b le 4 ( Y o u n g n e r, 1 9 6 1 a ). Figure 5. I n f l o r e s c e n c es of Kikuyu g r a s s. Male f e r t i le male s t e r i le ( l e f t) and ( r i g h t) Figure 6. E f f e c ts of day low length on f l o w e r- ing of Poa annua at temperature, P oa annua a g a in p r o v i d es an i n t e r e s t i ng e x a m p le of a t e m- p e r a t u r e - p h o t o p e r i od i n t e r a c t i o n. N o r m a l l y, P oa annua f l o w e r- ing is not r e s p o n s i ve to d ay length. H o w e v e r, s o me e c o t y p es f l o w er at c o ol t e m p e r a t u r es ( a p p r o x i m a t e ly 1 0 ° C) only if g i v en t e m p e r a- l o ng d a ys (16 h o u r s ), as shown in F i g. 6. At h i g h er t u r e s, f l o w e r i ng o c c u rs at any d ay l e n g t h. L o ng d a ys in t h is i n s t a n ce s e em to s u b s t i t u te f or w a rm t e m p e r a t u r es to p r o m o te f l o w e r i ng ( Y o u n g n er and W i l s o n, unpublished). Figure 7, t i l l e r- E f f e c ts of temperature on ing of t h r ee Poa p r a t e n s is c u l t i v a r s. T i l l e r i ng of K e n t u c ky b l u e g r a s s, P oa p r a t e n s i s, is h i g h ly t e m p e r a t u re s e n s i t i v e. T he o p t i m um t e m p e r a t u re f or t i l l e r- ing w i ll d i f f er f or v a r i o us c u l t i v a rs ( Y o u n g n er and Nudge, 1968b). As s h o wn in F i g. 7, N e w p o r t, a s e l e c t i on f r om the c o ol O r e g on c o a s t, h as a d i s t i n c t ly l o w er o p t i m um than M e r i on or 0217 F y l k i n g. T h is o b s e r v a t i on s u g g e s ts that v a r i e ty s e- l e c t i on f or s p e c i f ic c l i m a t es m ay be a step t o w a r ds m a i n t e- n a n ce of d e n se w e ed f r ee t u r f s. V C o n s i d e r a t i on of a c c u m u l a t i on of r e s e r ve c a r b o h y d r a t es g i v es f u r t h er s u p p o rt to t h is s u g g e s t i o n. R e s e r ve c a r b o h y- d r a t es a re thought to be h i g h ly i m p o r t a nt to a t u r f g r a s s 's a b i l i ty to r e c o v er f r om m o w i n g, i n j u ry or d i s e a s e, and to good r o ot and t i l l er g r o w t h. F i g u re 8 s h o ws that b l u e g r a s s es a c- c u m u l a te m o re c a r b o h y d r a t es at l ow t e m p e r a t u r es than at h i gh and that the c u l t i v a rs d i f f er in t h e ir a b i l i ty to s t o re c a r- b o h y d r a t es at any t e m p e r a t u r e. M e r i on is an e s p e c i a l ly good a c c u m u l a t er of c a r b o h y d r a t e s. V a r i e t i es b e t t er a b le to a c- c u m u l a te c a r b o h y d r a t es m ay be able to m a i n t a in g r e a t er v i g or and d e n s i t y, e s p e c i a l ly u n d er a d v e r se c o n d i t i o n s. A w e ak t u rf is m o re s u b j e ct to w e ed i n v a s i on than a v i g o r o us one. N i g h t - D ay T e m p e r a t u r es ( C e n t i g r a d e) Figure 8. E f f e c ts of temperature on carbohydrate accumu- l a t i on in t h r ee c u l t i v a rs of Poa p r a t e n s i s. S o me g r a s s es s u b j e ct to p e r i o ds of e x t r e me t e m p e r a t u re m ay l o se r e a e r ve c a r b o h y d r a t es q u i c k l y, as shown in F i g. 9. N i g ht t e m p e r a t u re in the 13 - 7 °C g r o w th c h a m b e rs w as o v er 3 5 °C f or t h r ee c o n s e c u t i ve n i g h ts d u r i ng the t w e l f th w e e k, r e s u l t i ng in s e v e re l o ss of c a r b o h y d r a t es ( M c K e ll et a l ., 1969), T h u s, t u r f g r a s s e s, s u ch as K e n t u c ky b l u e g r a s s, m ay be s u b j e ct to p e r m a n e nt i n j u ry f o l l o w i ng p e r i o ds of high t e m p e r a t u r e. H e r b i c i d es a p p l i ed at s u ch t i me could be h a r m f ul to the turf as w e ll as the w e e d. Figure 9. E f f e c ts of temperature on the r a te of carbohydrate three accumulation p r a t e n s i s, s e e d l i n g s. Night temperatures 13 - 7°C growth chambers were over 35°C f or n i g h ts during the t w e l f th week. in Newport Kentucky b l u e g r a s s, Poa in the T a b le 5. A c o r r e l a t i on of putting g r e en condition w i th o x y g en d i f f u s i on r a t es at d i f f e r e nt s o il d e p t h s. P u t t i ng G r e en D e p th of M e a s u r e m e nt C o n d i t i on ( i n c h e s) O x y g en D i f f u s i on R a te V a l ue (1) G o od B ad D e c l i n i ng 2 4 12 2 4 2 4 12 51.6 27.1 3.8 10.0 10.2 1 3 .6 14.7 4.1 (1) M e a s u r ed in g r a ms p er s q u a re c e n t i m e t er p er m i n u te ( a v e r a ge f or 20 m e a s u r e m e n t s ). An o x y g en d i f f u s i on r a te v a l ue of 20 is c o n s i d e r ed the c r i t i c al l e v e l. V a l- u es b e l ow t h is f i g u re w i ll not s u p p o rt s a t i s f a c t o ry g r o w th of g r a ss r o o t s. ( L e t ey et a l ., 1964) In the s a me f i g u r e, the e f f e c ts a re shown of continuous w a rm t e m p e r a t u r es (30 - 1 8 °C and 30 - 2 4 ° C) on c a r b o h y d r a te r e s e r v es of 7 - w e ek old b l u e g r a ss s e e d l i n g s. R e s e r v es w e re l ow at the t i me t e m p e r a t u re t r e a t m e n ts w e re s t a r t e d, and t h e re w as a s l i g ht but s t e a dy l o ss of r e s e r v es d u r i ng the s ix w e e ks of the e x p e r i m e n t. T h is i n d i c a t es that s u m m er p l a n t ed b l u e g r a ss t u r fs m ay be l e ss a b le to r e s i st i n j u ry and the r e s u l t i ng w e ed i n v a s i on than t u r fs s t a r t ed in the f a ll or e a r ly s p r i ng w h en t e m- p e r a t u r es a re c o n d u c i ve to c a r b o h y d r a te a c c u m u l a t i on ( M c K e ll et a l ., 1969). O t h er E n v i r o n m e n t al F a c t o rs In a s i m i l ar m a n n e r, o t h er e n v i r o n m e n t al f a c t o rs a f f e ct t u rf g r o w t h, d e n s i ty and v i g or and, c o n s e q u e n t l y, the t u r f 's a- b i l i ty to r e s i st w e ed i n v a s i o n. L e g u m e n o us w e e ds a re e s p e c- i a l ly c o m m on i n v a d e rs of n i t r o g en d e f i c i e nt t u r f, but m a ny o t h er s p e c i es m ay i n v a de a l s o. S i m i l a r l y, high s o il s a l i n i t y, a c o m m on p r o b l em of the s o u t h w e s t, w e a k e ns m a ny t u rf g r a s- s es and s u b j e c ts t h em to r e a dy i n v a s i on by s a lt t o l e r a nt w e e d s. D i s e a s e s, n e m a t o d es and i n s e c ts m ay a l so open the w ay f or i n- v a s i on by w e e d s. A c o m m on o b s e r v a t i on in s o u t h e rn C a l i f o r n ia is e x t e n s i ve k i ll of d i c h o n d ra t u rf f r om a c o m b i n a t i on of s e v- e r al f u n g o us p a t h o g e ns and r o o t - k n ot n e m a t o d e. T h is is u s u- a l ly f o l l o w ed by an i n v a s i on of c o m m on b e r m u d a g r a s s. S o il c o m p a c t i on and s o il l a y e r i ng r e s t r i ct o x y g en m o v e- is m e nt into the s o i l, o f t en r e s u l t i ng in p o or t u r f. T he turf r e a d i ly i n v a d ed by w e e d s, s u ch as P oa annua, that a re a b le to s u r v i ve u n d er l ow s o il o x y g en l e v e l s. L e t ey et al. (1964) s h o w ed that the o x y g en d i f f u s i on r a te on a p o or q u a l i ty putting g r e en w as only half of the r a te c o n s i d e r ed to be c r i t i c al f or g r o w th of g r a ss r o o ts ( T a b le 5). T he g r a ss on t h is g r e en w as a l m o st e n t i r e ly P oa annua. A n o t h er g r e en c o n s i d e r ed to be g o od q u a l i ty with m u ch b e n t g r a ss had o x y g en d i f f u s i on r a t es a b o ve the c r i t i c al l e v el at the 4 - i n ch depth but not at 12 i n c h e s. A e r i f i c a t i on is a s t a n d a rd r e m e dy f or t u rf s o il c o m p o s i- tion. L e t ey et a l. (1964) s h o w ed that a e r i f i c a t i on did i n c r e a se the o x y g en d i f f u s i on r a te ( T a b le 6). T he d e e p er and m o re e x- t e n s i ve the a e r i f i c a t i o n, the g r e a t er the i m p r o v e m e nt in the o x y g en d i f f u s i on r a t e. S o il o r g a n ic m a t t er is i m p o r t a nt to good plant g r o w t h. M a ny s o i ls u s ed f or t u rf a re n a t u r a l ly l ow in o r g a n ic m a t t e r, so v a r i o us o r g a n ic s o il a m e n d m e n ts a re o f t en added p r i or to p l a n t i n g. H o w e v e r, e s t a b l i s h ed t u rf b u i l ds i ts own o r g a n ic m a t t er t h r o u gh the death and d e c ay of r o o ts and o t h er plant p a r ts in the m i n e r al s o i l. A l t h o u gh t h is i m p r o v es the w a t er and n u t r i e nt r e l a t i o n s h i p s, it m ay a l so a f f e ct the u se of s o me s o il a p p l i ed h e r b i c i d es t h r o u gh i n c r e a s ed a d s o r p t i o n. Sandy s o i ls m i g ht be e s p e c i a l ly a f f e c t ed o v er a p e r i od of y e a rs with i n c r e a s ed a d s o r p t i on n e c e s s i t a t i ng i n c r e a s ed h e r b i c i de a p p l i- c a t i on r a t e s. T a b le 6. T he e f f e ct of t h r ee d i f f e r e nt a e r a t i on t r e a t m e n ts on the o x y g en d i f f u s i on r a te at d i f f e r e nt s o il depths u n d er put- ting g r e en c o n d i t i o n s. A e r a t i on T r e a t m e nt D e p th of M e a s u r e m e nt O x y g en D i f f u s i on (inches) R a te V a l ue (1) R e g u l ar 1. M e c h a n i c al P r o c e d u re (check) 2" H o l es 2. 10" D e ep B a c k f i l l ed with l o a m i te 1" H o le 3. 10" D e ep L e ft O p en 2 4 10 2 4 10 2 4 10 86.3 43.7 4.4 1 0 1 .7 69.2 22.7 95.0 7 2 .4 28.3 (1) M e a s u r ed in g r a ms p er s q u a re c e n t i m e t er p er m i n u te ( a v e r a ge f or 20 m e a s u r e m e n t s ). An o x y g en d i f f u s i on r a te v a l ue of 20 is c o n s i d e r ed the c r i t i c al l e v e l. V a l- u es b e l ow this f i g u re w i ll not s u p p o rt s a t i s f a c t o ry g r o w th of g r a ss r o o t s. ( L e t ey et a l ., 1964) , S u m m a ry It is a p p a r e nt that a ll e n v i r o n m e n t al f a c t o rs as t h ey p l ay u p on e a ch o t h e r, the t u rf g r a s s es and the w e ed p l a n t s, a f f e ct w e ed c o n t r o l. As t h e se f a c t o rs c h a n g e, c u l t u r al p r a c t i c e s, h e r- b i c i d e s, a p p l i c a t i on m e t h o d s, a p p l i c a t i on r a t es and t i m i ng of a p- p l i c a t i o n s, a ll m u st be a d j u s t ed in o r d er to a c h i e ve the b e st p o s- s i b le w e ed c o n t r o l. P r o p er t u rf c u l t u r al p r a c t i c es c an in t h e m- s e l v es r e d u ce w e ed p o p u l a t i o n s; n e v e r t h e l e s s, h e r b i c i d es a re an e s s e n t i al p a rt of m o st w e ed c o n t r ol p r o g r a m s. H o w e v e r, h e r b i- c i d es m u st be v i e w ed as f a c t o rs of the t o t al e n v i r o n m e n t, and t h e ir c o n s t a nt i n t e r a c t i on w i th a ll o t h er f a c t o rs n i z e d. By u s i ng t h em in t h is c o n t e x t, s a fe and e f f e c t i ve w e ed c o n t r ol c an be a c h i e v ed without u n n e c e s s a ry and u n d e s i r a b le c o n t a m i n a t i on of o ur e n v i r o n m e n t. O ur f a i l u re to p r o p e r ly r e c- o g n i ze h e r b i c i d es as c r i t i c al e n v i r o n m e n t al f a c t o r s, is at l e a st in p a rt r e s p o n s i b le f or the a d v e r se p u b l i c i ty and c r i t i c i sm g i v en t h em t o d a y. m u st be r e c o g- R e f e r e n c es C i t ed B i l l i n g s, W. D. 1952. T he e n v i r o n m e n t al c o m p l ex in r e l a t i on to plant g r o w th and d i s t r i b u t i o n. Q u a r t. R e v. B i o l. 2 7 : 2 5 1 - 2 6 5. B r o u g h a m, R. W. 1 9 5 7. S o me f a c t o rs that i n f l u e n ce the r a te of g r o w th of p a s t u r e. A s s o c. p. 1 9 0 - 1 1 6. 19th C o n f. of the N ew Z e a l a nd G r a s s l a n ds C a i n, S. A. 1944. F o u n d a t i o ns of P l a nt G e o g r a p h y. H a r p e r s, N ew Y o r k. D o n a l d, C. M. p. 1 - 1 1 8. A c a d. P r e s s, N ew Y o r k. 1963. C o m p e t i t i on a m o ng c r op and p a s t u re p l a n t s, In A. G. N o r m an (ed.), A d v a n c es in A g r o n o m y, G o o d, R. 1 9 3 1. A t h e o ry of plant g e o g r a p h y. N ew P h y t o l. 30: 1 4 9 - 1 7 1. G o o d, R. 1953. G e o g r a p hy of the F l o w e r i ng P l a n t. L o n g m a n s, G r e en and C o ., London. H o v i n, A. W. 1958a. M e i o t ic c h r o m o s o me p a i r i ng in a m p h i p l o id P oa annua. A m e r. J. B o t. 4 5 : 1 3 1 - 1 3 8. H o v i n, A. W. 1958b. R e d u c t i on of s e l f - p o l l i n a t i on by high night t e m p e r a t u re J o u r n. 5 0 : 3 6 9 - 3 7 1. in n a t u r a l ly s e l f - f e r t i l i z ed P oa annua L. A g r o n. J a m i s o n, D. A. and D. L. H u s s. 1959. T he e f f e ct of clipping l e a v es and s t e ms on n u m b er of t i l l e r s, h e r b a ge w e i g h t s, r o ot w e i g h t s, and f o od r e s e r v es of l i t t le b l u e s t e m. J. R a n ge M g m t. 1 2 : 1 2 2 - 1 2 6. L e t e y, J ., L. H. S t o l z y, O. R. Lunt and N. V a l o r i s. 1964. S o il o x y g en and c l i p p i ng h e i g ht e f f e c ts on the g r o w th of N e w p o rt b l u e g r a s s. C a l i f. T u r f g r. C u l t. 1 4 : 9 - 1 2. M a e d a, S. and K. E h a r a. 1962. P h y s i o l o g i c al and e c o l o g i c al s t u d i es on c l i p p i ng of h e r b a ge p l a n t s. P r o c. C r op S c i. S o c. J a p an 3 0 : 3 1 3 - 3 1 7. M a s o n, H. L. 1936. T he p r i n c i p l es of g e o g r a p h ic d i s t r i b u t i on as a p p l i ed to f l o r al a n a l y s i s. M a d r o no 3 : 1 8 1 - 1 9 0. M c K e l l, C. M ., V. B. Y o u n g n e r, F. J. N u d ge and N. J. C h a t- t e r t o n. 1969. C a r b o h y d r a te a c c u m u l a t i on of c o a s t al b e r- m u d a g r a ss and K e n t u c ky b l u e g r a ss in r e l a t i on to t e m p e r- a t u re r e g i m e s. C r op S c i. 9 : 5 3 4 - 5 3 7. S h e l f o r d, V. E. 1 9 1 3. A n i m al C o m m u n i t i es in T e m p e r a te N o r th A m e r i c a. Univ. C h i c a go P r e s s, C h i c a g o. T a y l o r, W. P. 1934. S i g n i f i c a n ce of e x t r e me and i n t e r m i t t e nt c o n d i t i o ns in d i s t r i b u t i on of s p e c i es and m a n a g e m e nt of n a t u r al r e s o u r c e s, with a r e s t a t e m e nt of L i e b i g 's l aw of the m i n i m u m. E c o l. 1 5 : 2 7 4 - 3 7 9. Y o u n g n e r, V. B. 1959. E c o l o g i c al s t u d i es on P oa annua in t u rf g r a s s e s. J. B r i t. G r a s s l d. S o c. 1 4 : 2 3 3 - 2 3 7. Y o u n g n e r, V. B. 1 9 6 1 a. L ow t e m p e r a t u re induced m a le s t e r- i l i ty in m a l e - f e r t i le P e n n i s e t um c l a n d e s t i n u m. 1 3 3 : 5 7 7 - 5 7 8. S c i e n ce Y o u n g n e r, V. B. 1 9 6 1 b. O b s e r v a t i o ns on the e c o l o gy and m o r- p h o l o gy of P e n n i s e t um c l a n d e s t i n um P h y t o n. 1 6 : 7 7 - 8 4. Y o u n g n e r, V. B. V e r t i c al m o w i n g - a e r i f i c a t i o n - a nd P oa annua i n v a s i o n. C a l i f. T u r f g r. C u l t. 18:6. Y o u n g n e r, V. B. and F. J. N u d g e. 1968a. C h e m i c al c o n t r ol of a n n u al b l u e g r a ss as r e l a t ed to v e r t i c al m o w i n g. C a l i f. T u r f g r. C u l t. 1 8 : 1 7 - 1 8. Y o u n g n e r, V. B. and F. J. N u d g e. 1968b. G r o w th and c a r b o h y- d r a te s t o r a ge of t h r ee P oa p r a t e n s is L. s t r a i ns as e n c ed by t e m p e r a t u r e. C r op S c i. 8 : 4 5 5 - 4 5 7. i n f l u- D i s c u s s i on P e r i od D r. H e m p h i l l: In r e f e r e n ce to the a c c u m u l a t i on of o r g a n ic m a t- t er b e l ow the thatch, how s i g n i f i c a nt is t h i s? How m u ch a c c u m u- lation of o r g a n ic m a t t er do we g e t? A re we r e a l ly the o r g a n ic m a t t er down at the 4 to 6 i n ch i n c r e a s i ng l e v e l? It s e e ms to me that we a r e, but I w as r a i s i ng D r. Y o u n g n e r: t h is as a q u e s t i on m y s e l f. I don't k n ow that we h a ve a lot of good e x p e r i m e n t al e v i d e n ce of t h i s, but the c a s u al o b s e r v a t i o ns that I h a ve m a d e, in r e s p e ct to o t h er s t u d i es and e x p e r i m e n t s, s e e ms to i n d i c a te that we w e re a c c u m u l a t i ng m o d e r a te a m o u n ts of o r- g a n ic m a t e r i al t h r o u gh r e p e a t ed d e c o m p o s i t i on of the root s y s t e m. I don't k n ow how long a t i me i n t e r v al m ay be r e q u i r ed f or this to o c c u r. T h is is w hy our b e st a g r i c u l t u r al s o i ls h a ve d e v e l o p ed o v er the a g es u n d er g r a ss conditions. P o s s i b ly the s a me thing w i ll be o c c u r r i ng in t u r f. It is c e r t a i n ly evident w h e re we a re g r o w i ng t a ll f e s c u e s, w h i ch h a ve an e x t r e m e ly a g g r e s s i ve w i d e- r a n g i ng root s y s t e m. D e c o m p o s i t i on of the r o ot s y s t em s e e ms to b r i ng about a d e f i n i te i m p r o v e m e nt of s o il s t r u c t u re o v er a p e r i od of t i me t h r o u gh o r g a n ic m a t t er a c c u m u l a t i o n. D r. L e d e b o e r: U n d er the f i ne g r a s s e s, though, we find that m o st of the root s y s t e m, o n ce a t h a t ch l a y er h as d e v e l o p e d, w i ll r e- m a in in that t h a t ch l a y e r. C o n s e q u e n t l y, the amount of a c c u m u- l a t i on of o r g a n ic m a t t er in the s o il i t s e l f, w h i ch b e c o m es quite c o m p a c t, is r a t h er l a y er on top. l i m i t e d. T he p r o b l em is in the t h a t ch I 'm quite s u re that is a l m o st u n i v e r s a l ly t r u e. D r. Y o u n g n e r: It is not u n u s u al to s ee t u rf g r o w i ng w h e re the e n t i re root s y s- t em is e s s e n t i a l ly in that a c c u m u l a t i on of thatch. Y ou c an r o ll the t u rf off the s o il l i ke a blanket. T h e re is v e ry little contact with the s o il b e l o w. I would l i ke to r a i se the q u e s t i o n, how would g r o w i ng the root s y s t em in p u re o r g a n ic m a t t er a f f e ct the u se of h e r b i c i d es ? D r. L e d e b o e r: T he p i c t u re is e n t i r e ly d i f f e r e nt with t a ll f e s c u e, s i n ce it r e a l ly d o es not f o rm thatch. In c a s es w h e re the h e r b i c i de I don't know of a lot of w o rk that h as b e en done D r. K a u f m a n: to a n s w er y o ur q u e s t i o n, only what we know about a d s o r p t i on of h e r b i c i d es to s o il o r g a n ic m a t t e r. is a d s o r b ed by t h is s o il o r g a n ic m a t t e r, I would think t h is e v e n- t u a l ly c o u ld b e c o me a p r o b l e m. M a ny of the c o m m on h e r b i c i d e s, l i ke the p h e n o xy c o m p o u n d s, m o ve r e a d i ly in s o il and a re not in- f l u e n c ed m u ch by o r g a n ic m a t t e r. T h ey p r o b a b ly w o u l d nft be a f- f e c t ed o v er a long t e r m. O t h er c o m p o u n ds w h i ch do not m o v e, s i m p ly b e c a u se t h ey a re a d s o r b ed on o r g a n ic m a t t e r, would be a f f e c t e d. A nd t h e se a re a l so s o me of the m o re p e r s i s t e n t. I 'm not s u re if the i n c r e a s ed p e r s i s t e n ce would be c o u n t e r a c t ed or o f f s et by the i n c r e a s ed a d s o r p t i o n. D r. Y o u n g n e r: T h is is a c o n c e rn only w h e re we a re d e a l i ng w i th h e r b i c i d es that a re a d s o r b ed on c l ay or o r g a n ic m a t t er the s o i l, and not t h o se d i f f e r e nt t y p e s. in M r. H o l y o k e: Would it be p o s s i b le to u se t h is o r g a n ic content d i f f e r e n t i al to e x p l a in the e f f e c t i v e n e ss of one h e r b i c i de b e- t w e en d i f f e r e nt r e g i o n s, e v en within a c l i m a t ic r e g i o n? We find c o m m e n ts that this one w o r ks f or me or this one g i v es t e r r i f ic d a m a ge in our a r ea and, p e r h a p s, it is the o r g a n ic m a t t er d i f f e r- e n t i a ls that c a u se the e f f e c t i v e n e ss or d a m a g e, or l a ck of d a m- a g e. Y ou get a d i f f e r e n t i al u n d er a p a r t i c u l ar condition that m i g ht be due to the a ge of y o ur p l o ts or the l o c a t i on of the p l o t s. So t h is is one of the t h i n gs that s o m e t i m es m a k es it d i f f i c u lt f or s o me of us who h a ve a l i m i t ed t u rf p r o g r am to u se r e s u l ts f r om o t h er s t a t e s. We get into p r o b l e ms and p e r h a ps i t 's b e c a u se of t h e se d i f f e r e n c es we j u st a r e n 't d u p l i c a t i n g. D r. A h r e n s: We h a ve to be c a r e f ul about what kind of o r g a n ic m a t t er w e ' re t a l k i ng about. M o st t h a t ch is l i ke peat. f i n e ly d i v i d ed and i ts p r o b a b ly not as a c t i ve in a d s o r b i ng h e r- b i c i d es as f i n e ly d i v i d ed o r g a n ic m a t t e r. w o rk w e ' ve done on c o n t a i n e rs in p e a t - s a nd m i x t u r e s, I e x p e ct m a y be 20% m o re h e r b i c i de r e- that t h e re m i g ht be a f a c t or of q u i r e d, but i t 's not going to be any big f a c t o r. Judging f r om the I t 's not O r g a n ic m a t t er in s o il g e n e r a l ly r e a c h es an e q u i l i b r i um f or a g i v en c l i m a t ic situation. We a re not going to get c o n t i n u al b u i l d - up of o r g a n ic m a t t e r. It w i ll r e a ch a p e ak and l e v el off f or the t e m p e r a t u re and s o il m o i s t u re condition. Y ou c an put 10 tons of m a n u re on a c o rn f i e ld e v e ry y e ar and n e v er get the o r g a n ic m a t t er l e v el a b o ve a c e r t a in point. h a p p en in t u r f, too. I think it w i ll D r. Y o u n g n e r: T h is is v e ry t r u e. H o w e v e r, in s o u t h e rn C a l- i f o r n i a, w h e re m a ny of our s o i ls a re n a t u r a l ly a l m o st d e v o id of o r g a n ic m a t t e r, we c an i n c r e a se the a m o u nt of o r g a n ic m a t- t er by a p p l y i ng an o r g a n ic a m e n d m e n t, or p o s s i b ly t h r o u gh the g r o w th of v e g e t a t i on o v er a p e r i od of t i m e. D r. S e e l y: W e ' ve got an o f f s e t t i ng f a c t or h e re that should be c o n s i d e r e d. W h e re we h a ve a r e l a t i v e ly high o r g a n ic m a t t er content and i r r i g a te as we do, we h a ve a m u ch h i g h er b i o l o g- i c al a c t i v i ty w h i ch t e n ds to d e c o m p o se the h e r b i c i d es a p p l i e d, as w e ll as a d s o r p t i o n. A l s o, we tend to l i b e r a te t h o se w h i ch a re a d s o r b e d. D r. Y o u n g n e r: T h a t 's a good point. D r. H o r n: We found that it t a k es f i ve pounds of the t r i a z i n es on our o r g a n ic m u ck s o i ls in F l o r i da to do the s a me j ob that t wo pounds w i ll do on a m i n e r al s o i l - - as f ar as a w e ed c o n- t r ol is c o n c e r n e d. I ' ve had s o me p l o ts g r o w i ng f or 13 y e a rs w h e re D r. H e m p h i l l: a n n u al a p p l i c a t i o ns w e re m a de with the s a me h e r b i c i d e. s ee a ny i n c r e a s ed d e m a nd to c o n t r ol c r a b g r a s s, and we o v e r- s e ed t h e se e a ch t i m e. A d m i t t e d l y, we did get s o me thatch. It is d i f f i c u lt f or s e ed to g e r m i n a te in this situation, but I h a v e n 't s e en a ny d e c r e a s ed l e v el of c o n t r ol with a g i v en r a te of D a c- t h a l, f or e x a m p l e. T h is is one of the h e r b i c i d es we h a ve b e en u s i ng the l o n g e s t. T he a r s e n a t es (lead and c a l c i um a r s e n a t e) h a ve b e en u s ed f or an e q u al length of t i m e, but I h a v e n 't s e en t h is n e ed f or an i n c r e a s ed l e v el of t r e a t m e n t. I don't D r. Y o u n g n e r: Y ou m ay h a ve a c h i e v ed the point of e q u i l i b r i um m e n t i o n ed e a r l i e r, w h e re t h e re w as no f u r t h er i n c r e a se in o r- g a n ic m a t t er in that s o i l, no m a t t er If t h is is the c a s e, you would continue to h a ve the s a me conditions and r e s u l ts with y o ur h e r b i c i d e s. what w as taking p l a c e. D r. S c h m i d t: I 'm s u re that m a ny of you a re f a m i l i ar with r e- s e a r ch at the S p o r ts T u rf Institute in B i n g l e y, E n g l a n d, w h e re the e f f e ct of a r s e n i c a ls a c t u a l ly i n c r e a s ed o r g a n ic m a t t e r. E v i d e n t l y, the p e s t i c i de had s o me e f f e ct or m i c r o b i al a c t i v i ty w i t h in the s o i l, so you c an h a ve a n o t h er i n t e r a c t i on h e re as f ar as the h e r b i c i de is c o n c e r n e d. I w as w o n d e r i ng I w o u ld l i ke you to v e r i fy a n o t h er point. if t h e re a re any data to s u p p o rt the f a ct that l o w er l e a v es a re p a r a s i t ic w h en shaded by l e a v es of o t h er s p e c i e s, or with l e a v es of the plant p er s e. As a m a t t er of i n f o r m a t i o n, one of o ur c o l l e a g u es at the V i r g i n ia P o l y t e c h n ic Institute h as data i n d i c a t i ng that the l o w er l e a v es a re not p a r a s i t i c, but in f a c t, the c a r b o h y d r a t es of t h e se dying l e a v es could be u t i l i z ed by the plant. C o n s e q u e n t l y, I q u e s t i on the s t a t e m e nt about the l o w er l e a v es being p a r a s i t i c. D r. Y o u n g n e r: As the l e af a r ea i n d ex b u i l ds up to the point w h e re it is o v er the o p t i m um ( c r e a t i ng a shading e f f e ct on the l o w er l e a v e s) and then you d e c r e a se the m o w i ng h e i g h t, you w o u ld s u p p o s e d ly r e m o ve m o st of the good a c t i ve l e a v e s. The r e m a i n i ng l e a v es w o u ld be s e n e s c e nt due to the l a ck of light. T h e se s e n e s c e nt l e a v es m u st be u s ed by the plant to r e c u p- e r a te u n t il it d e v e l o ps n ew l e a v e s. m u st c o n s i d e r. I think t h is is the point we I would l i ke to r e t u rn to the s u b j e ct of peat and D r. B i n g h a m: c h a r c o al f or a m o m e n t. S o me h e r b i c i d e s, b e n s u l i d e, f or e x- a m p l e, r e s p o nd r e a d i ly to a c t i v a t ed c h a r c o a l. Y e t, w h en c h a r- c o al w as a p p l i ed a f ew m o n t hs b e f o re this h e r b i c i d e, we ob- t a i n ed d r a s t i c a l ly r e d u c ed e f f e c ts of the c h a r c o a l. It s e e m ed that o n ce the c h a r c o al b e c o m es n e u t r a l i z ed in the s o i l, it w i ll not i n a c t i v a te the herbicid.e. A re t h e re any s o il p e o p le h e re w ho m i g ht be able to c l a r i fy t h i s? D r. A h r e n s: A lot of o t h er o r g a n ic c o m p o u n ds a re a d s o r b ed on c h a r c o al and peat. O n ce t h e se s i t es a re f i l l ed (by p h y s i- c al a d s o r p t i o n - - l a r g e ly on m i c r o - p o r es and m a c r o - p o r es c h a r c o a l ), h e r b i c i de a d s o r p t i on is r e d u c e d. C h a r c o al and p e at a l so a re e f f e c t i ve in a d s o r b i ng h e r b i c i d es only w h en the in p h y s i c al p l a c e m e nt is s u ch that the c h a r c o al or peat is in c o n- t a ct with the h e r b i c i d e. T h is p h y s i c al p l a c e m e nt is d i f f i c u lt to a c h i e v e, f or you m ay dilute the a d s o r b e nt at g r e a t er depths in the s o i l. T he h e r b i c i d e s, e s p e c i a l ly b e n s u l i d e, should be on the s u r f a c e. T h is m ay e x p l a in w hy the e f f e c t i ve could be ened w h en the c h a r c o al is a p p l i ed b e f o re the h e r b i c i d e. l e s s- D r. D a n i e l: One of the c u r r e nt s e e d i ng p r a c t i c es on b l u e g r a ss in the N o r t h w e st is r o ws about 18 i n c h es a p a r t. T he r o ws a re c o v e r ed with a t w o - i n ch s t r ip of c h a r c o a l, and then a p r e - e m e r- g e n ce h e r b i c i de is a p p l i ed that s t o ps g r o w th e v e r y w h e re e l s e. As long as the c h a r c o al i s n 't w a s h ed off, t h ey c an get a p e r f e ct stand. T HE N A T U RE OF B I O C H E M I C AL M E C H A N I SM OF H E R B I C I DE S E L E C T I V I TY S. W a y ne B i n g h am D e p a r t m e nt of P l a nt P a t h o l o gy and P h y s i o l o gy V i r g i n ia P o l y t e c h n ic Institute and State U n i v e r s i ty B l a c k s b u r g, V i r g i n ia 24061 I n t r o d u c t i on P h y s i o l o g i st and b i o c h e m i st h a ve m a de c o n s i d e r a b le p r o- in the u n d e r s t a n d i ng of b i o c h e m i c al a s p e c ts of h e r b i c i d e- g r e ss plant r e s p o n s e s. E s p e c i a l ly i m p o r t a nt a s p e c ts a re s t u d i es on the f a te of the h e r b i c i d al c h e m i c al i n s i de the plant, u n d e r s t a n d- ing of p h o t o s y n t h e s is as a r e s u lt of i m p o r t a nt h e r b i c i de r e a c- t i o n s, r a p id r e s p o n s es in R N A - D N A - P r o t e in y i e l d i ng b r o ad e f- f e c ts on m a ny d i f f e r e nt m e t a b o l i t e s, and p h y s i c al a c t i o ns of c h e m i c a ls on m e m b r a n e s. T he b a s is f or s e l e c t i v i ty v a r i es g r e a t ly f r om h e r b i c i de to h e r b i c i d e, and the i n t e r p r e t a t i on of the d i f f e r e nt b i o c h e m i c al r e s p o n s es f or a c h e m i c al in r e s i s t a nt v e r s us s u s c e p t i b le p l a n ts m u st a l so t a ke into a c c o u nt the i n t e r n al c o n c e n t r a t i o ns of the h e r b i c i d e. C e r t a i n l y, the i n t e n s i ty of the r e s p o n se v a r i es with the c o n c e n t r a t i on p r e s e n t. A d i f f e r e n t i al b i o c h e m i c al r e s p o n se b e t w e en r e s i s t a nt and s u s c e p t i b le plants m ay be a r e f l e c t i on of the i n t e r n al c o n c e n t r a t i o ns of the h e r b i c i d e. When d i f f e r e nt s p e c i es r e c e i ve s i m i l ar i n t e r n al c o n c e n t r a t i o n s, the b i o c h e m i- c al r e s p o n s es m ay w e ll be s i m i l a r. P l a n ts a l so v a ry in t h e ir m e t a b o l ic p a t h w a ys and at t i m es m ay s h i ft in r e s p o n se to v a r i o us i n h i b i t o r s. thought that s e l e c t i v i ty is r e l a t ed to (1) d e f e r e n t i al p e n e t r a t i o n, (2) d i f f e r e n t i al t r a n s l o c a t i o n, (3) d i f f e r e n t i al d e t o x i f i c a t i on or h e r b i c i de m e t a b o l i sm and (4) v a r i a t i on in plant m e t a b o l ic p a t h- w a y s. T he d u r a t i on of the t o x ic a c t i on is r e l a t ed to the a b i l i ty of the c o m p o u nd to r e a ch the site(s) of a c t i on and r a te at w h i ch it is m e t a b o l i z e d. T he b i o c h e m i c al t r a n s f o r m a t i o ns w h i ch h e r- It is p r e s e n t ly b i c i d es u n d e r go i n c l u d e: o x i d a t i on ( h y d r o x y l a t i o n, d e a l k y l a t i o n, c a r b o x y l a t i o n ), d e h y d r o g e n a t i o n, r e d u c t i o n, c o n j u g a t i on ( g l u c o- s i d e, m e t al c o m p l e x) and h y d r o l y t ic r e a c t i o n s. P h o t o s y n t h e s is and H e r b i c i d es M a ny of o ur b e st h e r b i c i d es a ct v ia p h o t o s y n t h e s i s, s e e m- i n g ly as the m a j or r e s p o n se in p l a n t s. T he c h l o r o p l a s ts a re o r g a n e l l es on w h i ch is c e n t e r ed the photo s y n t h e t ic a c t i v i ty of the c e l l. T h ey a re e a s i ly s e en with the light m i c r o s c o pe but t h e ir f i ne s t r u c t u re r e q u i r es h i g h er m a g n i f i c a t i o n. D i s c - s h a p ed o b- j e c ts in the c y t o p l a sm h a ve a l a m e l l ar s y s t em with a s t a ck of n e a r ly i d e n t i c al m e m b r a n es at v a r i o us points c a l l ed g r a n u m. T he p r o t e i n a c e o us m a t r ix is c a l l ed the s t r o ma and c o n t a i ns the e n z y m es i n v o l v ed in f i x a t i on of c a r b o n. T he c h l o r o p h y l ls and c o r o t e n o i ds a re in c l o se a s s o c i a t i on in the m e m b r a n es of the g r a n a, a l l o w i ng f or e f f i c i e nt t r a n s f er of light e n e r g y. In e a r ly w o r k, the o v e r a ll r e a c t i on of p h o t o s y n t h e s is w as d e m o n s t r a t e d: «>2 + H20 chloroplast > C H2° + °2 A f u r t h er i m p o r t a nt d i s c o v e ry p r o v i d ed c o n v i n c i ng e v i d e n ce t h at the o x y g en r e l e a s ed in p l a n ts w as f r om w a t e r, not c a r b on d i o x i d e: C°2 + 2 »2°* chloroplast"' + °2 + ^ S u m m a ry r e a c t i o ns of p h o t o s y n t h e s is a re now d i v i d ed into t wo g e n e r al g r o u ps of r e a c t i o n s, one known as the light r e a c t i o n s: Chloroplast 4- H20 + ADP + Pi + NADP 1 : Lgh t>^ O2 + ATP + NADPH T he s e c o nd as d a rk r e a c t i o n s: Chloroplast + C 02 + ATP + NADPH NADP > sugar + ADP + Pi + O t h er e s s e n t i al c o m p o u n ds h a ve b e en i d e n t i f i ed in c h l o r o- p l a s t, p r o v i d i ng the a b i l i ty f or a l t e r n a te o x i d a t i on and r e d u c t i on and p a r t i c i p a te in e l e c t i on t r a n s p o r t. T h e se i n c l u de c y t o c h r o me f, p o s s i b ly c y t o c h r o ne b£>, p l a s t o q u i n o n e s, p l a s t o c y a n i n, f e r r e- d o x in and t h e re a re o t h e rs y et u n i d e n t i f i ed ( S a l i s b u ry and R o s s, 1969). T h e n, a m o d el f or the l i g ht r e a c t i o ns of p h o t o s y n t h e s is m ay be shown: S y s t em II accepts e l e c t r on In S y s t em I, light e n e r gy m ay be c o n v e r t ed to c h e m i c al e n e r gy of A TP t h r o u gh e l e c t r on f l ow b a ck to c h l o r o p h y ll (P700). T he p r o c e ss is c a l l ed photo s y n t h e t ic p h o s p h o r y l a t i o n. a n o t h er p a t t e rn of e l e c t r on f l o w, t h ey a re c a p t u r ed by N A D P, f o r m i ng the r e d u c ed p y r i d i ne n u c l e o t i d e. N A D PH and A TP a re p r o d u c ts s t o r i ng the e n e r gy of light and a s s i m i l a t o ry p o w er f or the d a rk r e a c t i o n s. C h l o r o p h y ll b a p p e a rs to be a s s o c i a t ed with the s p l i t t i ng of w a t er and functioning of n o n - c y c l ic p h o s p h o r y l a- tion in S y s t em II. In U r ea H e r b i c i d es C o o ke (1956) and W e s s e ls and V an d er V e en (1956) c o n c l u d ed i n t e r f e re with the o x i d a t i on of w a t e r. M o n- t h at u r ea h e r b i c i d es u r on w as o b s e r v ed to i n t e r f e re with the e l e c t r on f l ow s y s t em that p r o v i de l ow e n e r gy e l e c t r o ns to f i ll the h o l es in the c h l o r o p h y ll a, or P 7 00 ( J a g e n d o rf and M a r g u l i e s, I960). A ll e v i d e n ce s u p p o r ts the c o n c l u s i on that i n t e r f e r e n ce o c c u r r ed in the n o n - c y c l ic p o r t i on of the e l e c t r on f l ow s y s t e m s. A c c u m u l a t i on of o x i d i z ed c y t o c h r o me o c c u r r ed and e l e c t r o ns w e re not r e t u r n ed to c h l o r p h y l l. A d i s c u s- s i on by v an O v e r b e ek (1962) s u g g e s t ed that, e v e n t u a l l y, c h l o r o p h y ll m o l e c u l es b e c o me o x i d i z ed to the point that b l e e c h i ng o c c u r s. T h is w o u ld e x p l a in the c h l o r o s is and c o l l a p se of the t i s s u e s. It s e e ms o b v i o u s, h o w e v e r, though p h o t o s y n t h e t ic r e s p o n s es a p p e ar the m a j or e f f e ct of u r ea h e r b i c i d e s, that s t a r v a t i on is not a c o m- p l e t e ly s u f f i c i e nt e x p l a n a t i on f or t h e ir a c t i on ( C r a f t s, 1 9 6 1; J o r d an et a l ., 1966). S u g a rs a l l e v i a te the h e r b i c i d es s y m p t o m s, p o s s i b ly by r e s p i r a t i on w h i ch p r o v i d es e l e c t r o ns to r e p l e n i sh c y t o c h r o m e s, c h l o r o p h y ll and o t h er m o l e c u l es r e t a i n ed in the o x i d i z ed state by h e r b i c i d al a c t i v i t y. A s c o r b a te and 2 , 6 - d i c h l o r o p h e n o l i n d o p h e n ol y i e l d ed e l e c t r o ns to the s y s t em to c i r c u m n e nt the inhibition of the u r ea h e r b i c i d e s. U r a c i l, T r i a z i ne and A n i l i de H e r b i c i d es M o r e l a nd et a l. (1959) h a ve found p h o t o s y n t h e s is to be a m a j or i n t e r- in w h i ch t h e se t h r ee f a m i l i es of h e r b i c i d es c a u s es p r o c e ss f e r e n c e; in p a r t i c u l a r, the r e t u rn of e l e c t r o ns to c h l o r o p h y l l. With s i m i l ar b i o l o g i c al a c t i o n, it a p p e a rs that t h e ir m o l e c u l es m u st h a ve f e a t u r es in c o m m o n. C h e m i c a l l y, t h ey a re r a t h er u n r e a c t i ve and, t h u s, a p p e ar u n l i k e ly that a c t i v i ty is due to c o v a l e nt bond r e a c t i o n s. T h e se h e r b i c i d es h a ve an NH g r o up in c o m m on and h y d r o g en bond- ing is w e ll known with s u ch g r o u p s. T h e re is a l so C O or -C N- g r o u ps n e xt to the NH g r o up in e v e ry c a se and t h ey m ay g i ve s i m- i l ar h y d r o g en bonds. T h u s, the high b i o l o g i c al a c t i v i ty s e e ms to be r e l a t ed to a c a p a c i ty to f o rm h y d r o g en bonds with the p r o t e in of e n z y m es as w e l l. F u r t h er s u p p o rt of h y d r o g en bonding a s p e c ts w e re d e m o n s t r a t ed by r e p l a c i ng the h y d r o g en on the NH g r o up with an e t h yl g r o up and o b s e r v i ng m u ch r e d u c ed a c t i v i ty on the photo- s y n t h e t ic p r o c e s s. S i d u r o n, a n o t h er u r ea h e r b i c i d e, d o es not a p p e ar to i n t e r f e re w i th the p h o t o s y n t h e t ic p r o c e ss as m o n u r on d o es and H o p e n, 1968). d r a n ce m ay be a p o s s i b i l i t y. It h as the two f u n c t i o n al g r o u p s, but s t e r ic h i n- ( S p l i t t s t o e s s er D i u r on and s e v e r al N - p h e n yl c a r b a m a t es w e re found to a b s o rb to b o v i ne s e r um a l b u m in ( a n i m al p r o t e in - B S A ). Sub- s t i t u t i on of c h l o r i ne in the 3 and 3 , 4 - p o s i t i o ns of the p h e n yl ring w as c o r r e l a t ed with i n c r e a s ed a b s o r p t i on to B SA ( C a m p er and M o r e l a n d, 1966). T h is a p p e a r ed to a l t er the e l e c t r on d e n s i ty so that the a m i de h y d r o g en b e c a me m o re a c i d i c. T he s o r p t i on of d i u r on and p r o p a n il to plant p r o t e in w as s e v e r al f o ld g r e a t er than to B SA ( C a m p er and M o r e l a n d, 1967). S o r p t i on a p p e a r ed to be b e t w e en the a m i de g r o up of the h e r b i c i de and a m i no g r o u ps of the p r o t e i n. T he s o r p t i on w as t e m p e r a t u re dependant s u g g e s t i ng CI w e ak b o n d s, s u ch as h y d r o g en bonding. At c e r t a in h e r b i c i de l e v e l s, i n c o r p o r a t i on of l e u c i ne and n u c l e o t i d es into p r o t e in w as i n h i b i t e d. L ow l e v e ls of t r i a z i ne h e r b i c i de i n c r e a s ed p r o t e in c o n t e nt of s e v e r al plant s p e c i e s. B i p y r i d y l i um H e r b i c i d es T he b i p y r i d yl h e r b i c i d es do not h a ve the h y d r o g en bonding c h a r a c t e r i s t ic of the o t h er photo s y n t h e t ic i n h i b i t o rs and a p p e ar to p i ck up an e l e c t r on d e s t i ne to r e d u ce N A DP ( F u n d e r b u rk and L a w r e n c e, 1964; M e e s, I960). T he h e r b i c i d al a c t i v i ty m i g ht be r e l a t ed to the f o r m a t i on of f r ee r a d i c a ls by t r o n. S y s t em II, as d e s c r i b ed p r e v i o u s l y, is inhibited by u r e a, t r i a z i n e, u r a c il and a m i l i d e s, w h i le S y s t em I m ay r e m a in f u n c- t i o n a l. S y s t em I is a f f e c t ed by the b i p y r i d yl h e r b i c i d e s. the uptake of one e l e c- R e s p i r a t i on and H e r b i c i d es R e s p i r a t i on is u s u a l ly d e s c r i b ed in t h r ee or m o re p h a s e s, is the p r o c e ss by w h i ch s t a r ch is b r o k en down into i n c l u d i ng g l y c o l y s i s, K r e bs c y c le and e l e c t r on t r a n s p o rt s y s t e m. G l y c o l y s is p y r u v ic a c i d. T he K r e bs c y c le f u r t h er b r e a ks down p y r u v ic a c id to CC>2 and, e v e n t u a l l y, t h r o u gh the e l e c t r on t r a n s p o rt s y s t e m, H2O. M a ny h e r b i c i d es show v a r i o us e f f e c ts on t h e se p r o c e s s e s. As d e s c r i b ed p r e v i o u s l y, c h e m i c a ls c an f o rm h y d r o g en bonds or b e c o me a b s o r b ed to p r o t e in and c a u se v e ry g e n e r al r e s p o n s es a m o ng the m a ny e n z y me c o n t r o l l ed r e a c t i o n s. H o w e v e r, s o me c h e m i c a ls (I) r e a ct with or c o m p l ex with e n z y m es (E) a s: E 4- I £ 5 E I E-SH + I-OH £ ^ E - S -I + HOO A r s e n i c al H e r b i c i d es T he e n z y m e, p h o s p h o g l y c e r a l d a h y de d e h y d r o g e n a s e, c o n- t a i ns s u l f h y d r yl g r o u ps that a re e s s e n t i al to the o x i d a t i on of g l y- c e r a l d e h y de 3 - p h o s p h a te to d i p h o s p h o g l y c e r ic a c id 1 , 3 - d i p h o s- p h a t e: E-SH 4- NADP + HC=0 < > E-S-C=0 4- NADPH A / /-\tt \ HCOH HCOH HCOH / H2COPO3H2 As (OH) 3 H2O H e re the e n z y me r e a c ts w i th the s u b s t r a te r e s u l t i ng in an a c y l t h i o e s t er of the e n z y me and a n u c l e o p h i l ic a g e n t, P i, f o r m- ing the d i p h o s p h a te ( S a l i s b u ry and R o s s, 1969). T he f i r st r e a c- t i on of the a r s e n a te h e r b i c i de is to t ie up the f u n c t i o n al g r o up of the e n z y m e, r e n d e r i ng it i n a c t i v e. A s e c o nd type inhibition m ay be d e s c r i b ed a s: Substrate (S ) + I > I + s2 A r s e n a te e x h i b i ts e x t r e me t o x i c i ty in t h is m a n n er r e d u c i ng or b y p a s s i ng p h o s p h o r y l a t i on of A D P. M a ny a r s e n a te h e r b i c i d es s h ow t h e se b i o c h e m i c al m e c h a n i s ms in p l a n t s. T h is d o es not e x p l a in the s e l e c t i ve c o n t r ol of w e e ds with a r s e n a t e; but a m o ng m a ny o t h er f a c t o r s, r e l a t i ve p e n e t r a t i on of t h e se h e r b i c i d es into d i f f e r e nt t i s s u es and c o n v e r s i on of the v a r i o us f o r ms to a r s e n ic a c i d, o f f er s o me e x p l a n a t i on f or s e l e c t i ve c o n t r o l. T he r e s p o n se f r om a r s e n a te c an p a r t i a l ly be c o u n t e r a c t ed with p h o s p h a te t i l i z er s u p p o r t i ng the c o m p e t i t i ve r o le shown a b o v e. f e r- A r s e n a te r e a c ts with s u l f h y d r yl g r o u ps of m a ny e n z y m es and, upon p e n e t r a t i on of the s y m p l a s t, c a u s es p r o t e in to p r e c i p- i t a t e, b e c o m i ng l e ss a v a i l a b le f or plant p r o c e s s e s. C h l o r i n a t ed A l i p h a t ic H e r b i c i d es D a l a p on and T CA p r e c i p i t a te p r o t e in and c a u se m a ny t y p es in p l a n t s. D a l a p on w as found to bind with p r o t e in of r e s p o n s es to c h a n ge c o n f i g u r a t i on of an e n z y m e, r e s u l t i ng in i n a c t i v a t i on ( K e mp et a l ., 1969). H y d r o g en bonding is p r o p o s ed s c h e me a s: \ D a l a p on p r o v i d ed c o m p e t i t i ve inhibition of pantothenate b i o- s y n t h e s is as the c h e m i c al s t r u c t u re r e s e m b l es s o m e w h at both s u b s t r a t es (Hilton, 1966): H O - C H2—C CH3 0 - C H —C - I CH3 \ OH NH2 OH 4- CH2-CH2 — COOH HQ C- If 0 CH 2— CH 2— NH — C — CH - C~ 0 it CH-3 OH -CH^ Competitive I n h i b i t or OH CH. CH3— C— COOH Cl I •C- I CI Dalapon P a n t o t h e n a te is e s s e n t i al f or c o e n z y me A p r o d u c t i o n. P e r- h a ps d a l a p on a c ts as an a n t i m e t a b o l i te f or p y r u v ic a c id as t h e ir c h e m i c al s t r u c t u r es r e s e m b le e a ch o t h e r. A l t h o u gh the c h l o r i- n a t ed a l i p h a t i cs i n t e r f e re with s u ch r e a c t i o n s, at high c o n c e n t r a- t i o ns t h ey a re v e ry e f f e c t i ve p r o t e in d e n a t u r a n ts and m ay be a c t- ing s i m p ly as e n z y me d e n a t u r a n t s. A m i t r o le T he i m m e d i a te r e s p o n se of p l a n ts to a m i t r o le is a s t r i k i ng c o l or c h a n ge r e s u l t i ng in b l e a c h ed white t i s s u e. T he c h l o r o s is m ay be independent of the g r o w t h - i n h i b i t i ng a c t i o ns r e s p o n s i b le f or h e r b i c i d al a c t i o n s. A m i t r o le t i d i n e, r i b o f l a v in and, p o s s i b l y, n u c l e ic a c id and p u r i ne m e t a b o- l i s m. T he step in h i s t i d i ne b i o s y n t h e s is b l o c k ed by a m i t r o le (Hilton and K e a r n e y, 1965): inhibits b i o s y n t h e s is of h i s- EC NH CH -N' HCOH I HCOH / H2COPO3H2 Imidazole g l y c e r ol phosphate dehydrogenose ^ H2O H C — N H, SCH N C I CH2 C=0 This r e a c t i on is blocked by H2C 0 P 03H2 Imidazole a c e t ol phosphate N=CH \ NH C=N ' I NH0 Amitrole 34 S o me of the p r e v i o us s u b s t r a t es a c c u m u l a te f o l l o w i ng a m i- t r o le t r e a t m e n t. H o w e v e r, the c o m p e t i t i ve inhibition c an be c o u n t e r a c t ed by p r o v i d i ng i m i d a z o le a c e t ol p h o s p h a te to f o rm h i s t i d i n e. T he b i o s y n t h e s is of p o r p h y r in s e e ms to be a l i k e ly p l a ce f or a m i t r o le i n t e r f e r e n ce in p l a n t s. P o r p h y r in s t r u c t u r es a p p e ar in m a ny plant c o n s t i t u e n t s, s u ch as the c h l o r o p h y l ls and c y t o- c h r o m e s. M a ny e n z y m es contain t h is c o m p o n e n t. One r e s p o n se of p l a n ts to a m i t r o le is the l o ss of c h l o r o p h y ll and p r e v e n t i on of n ew m o l e c u l e s. T he s y n t h e s is of p o r p h y r in h as s e v e r al s t e ps f r om s u c c i n y l - C oA to u r o p o r p h y r i n g e n, and the a m i t r o le s t r u c- t u re is quite s i m i l ar to a c o u p le p r e c u r s o rs a s: P o s s i b le i n h i b i t or amitrole A c o n j u g a te of a m i t r o le and s e r i ne m ay a l so p l ay a r o le in i n t e r f e r e n c e: C h l o r o p h y ll content d e c l i n es a f t er h e r b i c i d al a p p l i c a t i o ns of a m i t r o l e, and this l ed to s p e c u l a t i on of t h is type T he a b u n d a n ce of t h is c o n j u g a te in c h l o r o t ic t i s s ue m ay be a s s o c i- a t ed with the inhibition of c h l o r o p h y ll s y n t h e s is and p l a s t id p r o- d u c t i o n. i n t e r f e r e n c e. C o n v e r s i on of I n a c t i ve to A c t i ve H e r b i c i d es M e m b e rs of the p h e n o x y a l k a n e c a r b o x y l ic a c id s e r i es with If t h e re is an l o n g er side c h a i ns than 2 , 4 -D a re i n a c t i ve p er s e. e v en n u m b er of c a r b o ns in the side c h a i n, the m o l e c u le is c o n- v e r t ed to 2 , 4 -D by b e t a - o x i d a t i on ( S y n e r h o lm and Z i m m e r m a n, 1947): P h e n y l c a p r y l ic P h e n y l c a p r o ic P h e n y l b u t y r ic P h e n y l a c e t ic With odd n u m b er of c a r b o ns in the side c h a in and beta oxi- d a t i o n, b e n z o ic a c id is p r o d u c ed as the a c t i ve agent: P h e n y l v a l e r ic P h e n y l p r o p i o n ic ^ b e n z o ic B e t a - o x i d a t i on m e c h a n i sm a p p e a rs a s: T he f o l l o w i ng d i a g r am s h o ws the n o r m al b e t a - o x i d a t i on of v a r i o us n - p h e n o x y a l k a n e c a r b o x y l ic a c i d s: Heptanoic Caproic V a l e r ic B u t e r ic Propionic A c e t ic Phenol S o me p l a n ts cannot c a r ry out b e t a - o x i d a t i on or do so at a v e ry s l ow r a te and l i ve w h i le o t h er plants c o n v e rt the m o l e c u le to the a c t i ve f o rm r a p i d ly and d i e. T he p r a c t i c al u s es a p p e ar with c e r t a in w e e ds in l e g u m i n o us c r o ps u s i ng b u t y r ic f o r ms of p h e n o xy h e r b i c i d e s. M C PB and 2 , 4 - DB w e re m o st p r o m i s i ng as w e ed c o n t r ol m a t e r i a l s. S e s o ne is a l so c o n v e r t ed to 2 , 4 -D in the soil: T h is c o n v e r s i on o c c u rs in s o il but not on f o l i a ge of h i g h er p l a n t s. T he c o n t r ol obtained is p r i m a r i ly p r e e m e r g e n ce and K a u f m a n, 1969). ( K e a r n ey C o n v e r s i on of A c t i ve to I n a c t i ve ( L e ss A c t i v e) F o r ms of C h e m i c al E a r ly r e s e a r ch on t r i a z i ne i n a c t i v a t i on s u g g e st that 2- c h l o ro d e r i v i t i v es w e re c o n v e r t ed n o n - e n z y a e t i c a l ly in the p r e- s e n ce of B e n z o x a z i n o ne to 2 - h y d r o xy f o r m s. L a t e r, it a p p e a r ed that the side chain w as l o st as a p a r t i al m e a ns f or r e d u c i ng the t o x i c i ty (Shimabukuro et a l ., 1970). T h is f o r m ed l e ss toxic c h e m i c a l s, but they w e re s t i ll s o m e w h at a c t i ve f or r e d u c i ng the photosynthetic r a t e. M o re r e c e nt r e s e a r ch h as shown the rapid f o r m a t i on of a glutathione - a t r a z i ne conjugate to be involved in s e l e c t i v i t y: CH3 T h is conjugate w as f u r t h er m e t a b o l i z ed t oy - L - g l u t a m yl - s - ( 4 - e t h y l a m i no - 6 - i s o p r o p y l a m i no - 2 - s - t r i a z i n e) - L - c y s t e i ne w h i ch is a dipeptide c o n j u g a t e. S u s c e p t i b le plants w e re l ow in glutathione s - t r a n s f e r a se w h i ch a p p e a r ed to be r e q u i r ed f or c o n j u g a t i on of a t r a z i ne and glutathione (Shimabukuro and Swanson, 1969). U r ea h e r b i c i de m e t a b o l i sm m ay a l so p l ay an i m p o r t a nt r o le in s e l e c t i v i ty ( S w a n s on and S w a n s o n, 1968). A d e m e t h y l a t i on p a t h w ay h as b e en d e m o n s t r a t e d: P l a n t a in and cotton w e re quite e f f e c t i ve f or d e m e t h y l a t i on of d i u r on w h i le m o re s u s c e p t i b le c o rn and s o y b e an w e re unable to c a r ry out the c o m p l e te i n a c t i v a t i o n. C h l o r o x u r on and m o n u- r on f o l l ow a s i m i l ar p a t h w ay ( K e a r n ey and K a u f m a n, 1969). P r o p o s ed N - d e m e t h y l a t i on r e a c t i o ns f or u r ea and a m i de h e r b i c i de s i d e c h a i ns p r o c e ed a s: C e r t a in g r a s s es w e re found to h y d r o x y l a te d i c a m ba and fo rm a g l u c o s i de ( C o o k e, 1956): (urea h e r b i c i de side chain) T h is m ay be a m a j or f a c t or in s e l e c t i v i ty f or w e ed c o n t r ol in b l u e g r a s s. B l u e g r a ss r e c e i v es s o me i n i t i al e f f e c ts w h i ch s e em to d e m i n i sh a f t er p e r i o ds of t i m e. p e r c e n t a ge of the d i c a m ba in two d a y s. It m e t a b o l i z es a high D C PA d o es not a p p e ar to be a b s o r b ed and t r a n s l o c a t ed r e a d i ly and i n a c t i v a t i on h as b e en e v a l u a t ed p r i m a r i ly in soil. M i t o s is in root t i ps a p p e a r ed to be a m a j or p r o c e ss a f f e c t ed by D C PA ( B i n g h a m, 1968). (DCPA) P h e n o xy H e r b i c i d es A u x i n - t y pe h e r b i c i d es h a ve b e en o b s e r v ed to r e l a te to so m a ny r e s p o n s es that it m ay be r a t h er d i s a p p o i n t i ng b e c a u se v e ry l i t t le s p e c i f ic i n f o r m a t i on c an be s a id about the m o de of s e l e c t i ve a c t i o n. M a ny m e t a b o l i t es and e n z y me a c t i v i t i es a p- p e ar to c h a n ge in r e s p o n se to t r e a t m e nt with 2 , 4 - D. T he e v i- d e n ce is gaining t o w a rd a p o s t u l a t i on that 2 , 4 -D is a c t i ng upon the R N A - D N A- p r o t e in s y s t e m. H e r b i c i d al c o n c e n t r a t i o ns of 2 , 4 -D i n c r e a s ed the R NA and p r o t e in of s t em t i s s ue (West et a l ., 1960). L ow c o n c e n t r a t i o ns p r o m o te R NA l o ss as shown by i n c o r p o r a t i on s t u d i es with b e l ed n u c l e o t i d es and m e t a b o l ic b r e a k d o wn of p r e e x i s t i ng R NA ( K e y, 1963). E v en if the a c t i on of 2 , 4 -D r e v o l v es a r o u nd the l a- D N A - R N A - p r o t e in s y s t e m, we s t i ll r e m a in e s s e n t i a l ly without u n d e r s t a n d i ng of the m e c h a n i sm of b i o c h e m i c al s e l e c t i v i t y. T h e re is e v i d e n ce that 2 , 4 -D is m e t a b i o l i c a l ly m o re r a p i d ly in r e s i s t a nt than in s u s c e p t i b le s p e c i es and L l o y d - J o n e s, I960). It is a l so f e lt that one p h e n o xy h e r b i- c i de m ay be m o re e f f e c t i ve than a n o t h er on a g i v en s p e c i es due to the p l a n ts i n a b i l i ty to m e t a b o l i ze the h e r b i c i de (Slife et a l ., 1962). i n a c t i v a t ed ( L u c k w i ll T he r a p id d e g r a d a t i on of the 2 , 4 -D side c h a in a p p e a rs to be p a r t i a l ly r e s p o n s i b le f or r e d u c i ng t o x i c i ty t o w a rd v a r i o us p l a n t s. H o w e v e r, not a ll r e s i s t a nt p l a n ts d e c a r b o x y l a te 2 , 4 -D at s i g n i- f i c a nt r a t e s, s u g g e s t i ng o t h er m e c h a n i s m s. T he c o n j u g a t i on of p h e n o xy h e r b i c i d es with plant c o n s t i t u e n ts a p p e a rs to p r o v i de a n o t h er m e c h a n i sm ( K e a r n ey and K a u f m a n, 1969). A s p a r t ic acid 2,4-D 2 , 4 - D - a s p a r t ic conjugate H y d r o x y l a t i on of the r i ng of 2 , 4 -D p r i or to f o r m i ng a c o n- j u g a te h as a l so b e en d e m o n s t r a t e d: M a ny c o n j u g a t es s i m i l ar to the a b o ve h a ve b e en d e m o n s t r a t ed u n d er s e v e r al plant s i t u a t i o ns and a p p e ar as a s e l e c t i ve m e c h a n i s m. T he m e t a b o l ic a s p e c ts of p l a n ts upon the h e r b i c i de m o l e c u le a re not the only f a c t o rs in the s e l e c t i v i ty m e c h a n i s m. A b s o r p t i on and t r a n s l o c a t i on a re quite i m p o r t a nt a s p e c t s. R e f e r e n c es C i t ed B i n g h a m, S. W. 1968. E f f e ct of D C PA on a n a t o my and c y t o l o gy of r o o t s. W e ed S c i. 1 6 : 4 4 9 - 4 5 2. B r o a d h u r s t, N. A ., M. L. M o n t g o m e ry and Y. H. F r e e d. 1966. M e- t a b o l i sm of 2 - m e t h o x y - 3 , 6 - d i c h l o r o b e n z o ic a c id ( d i c a m b a) by w h e at and b l u e g r a ss p l a n t s. J. A g. F o od C h e m. 14:585-588. C a m p e r, W. D. and D. E. M o r e l a n d. 1966. A d s o r p t i on of h e r b i c i d es to p r o t e i n s. P. 32 W e ed S o c. A m e r. ( A b s t r .) C a m p e r, W. D. and D. E. M o r e l a n d. 1967. S o r p t i on of d i u r on and p r o p a n il to p r o t e i n. P. W e ed S o c. A m e r. ( A b s t r .) C o o k e, A. R. 1956. A p o s s i b le m e c h a n i sm of a c t i on of the u r ea type h e r b i c i d e s. W e e ds 4 : 3 9 7 - 3 9 8. C r a f t s, A. S. 1 9 6 1. T he c h e m i s t ry and m o de of a c t i on of h e r b i c i d e s. I n t e r s c i e n ce p u b l i s h e r s, N ew Y o r k. pp. 269. E n g e l, R. E. 1969. S e l e c t i v i ty of t u r f g r a ss h e r b i c i d e s. 1 st Intl. T u r f g r a ss Conf. P r o c. 4 p. F u n d e r b u r k, H. H. and J. M. L a w r e n c e. 1964. M o de of a c t i on and m e t a b o l i sm of diquat and p a r a q u a t. W e e ds 12:259-264. G e i s s b u h l e r, H., C. H a s e l b a c h, H. A e bi and L. E b n e r. 1963. T he f a te of Nl - ( 4 - c h l o r o p h e n o x y ) - p h e n y l - N, N - d i m e t h y- l u r ea ( C - 1 9 8 3) in s o i ls and p l a n t s. W e ed R e s. 3 : 2 7 7 - 2 9 7. H i l t o n, J. L. 1966. A l i p h a t ic a c id i n h i b i t o r: i n t e r f e r e n ce with k e t o p a n t o a te u t i l i z a t i on f or p a n t a l h e n a te b i o s y n t h e s i s. W e e ds 1 4 : 1 7 4 - 1 7 6. H i l t o n, J. L. and P. C. K e a r n e y. i n t e r f e r e n ce w i th a d e n i n e - 2 - ^C m e t a b o l i sm by S a c c h a r o m y c es c e r e n- i s i a e. W e e ds 13:22-25. 1965. A m i t r ol J a g e n d o r f, A. T. and M. M a r g u l i e s. 1960. Inhibition of s p i n a ch c h l o r o p l a st photo s y n t h e t ic r e a c t i o ns by p - c h l o r o p h e n y l - 1, 1 - d i m e t h y l u r e a. A r c h. B i o c h e m. and B i o p h y s. 90:184-195. J o r d a n, L. S., T. M u r a s h i g e, J. D. Mann and B. E. D a y. 1966. E f f e ct of photo s y n t h e t i c - i n h i b i t i ng h e r b i c i d es on n o n - p h o t o- s y n t h e t ic t o b a c co c a l l us t i s s u e. W e e ds 1 4 : 1 3 4 - 1 3 6. K e a r n e y, P. C. and D. D. K a u f m a n. E d. 1969. D e g r a d a t i on of h e r b i c i d e s. M a r c el D e k k e r, Inc. N ew Y o r k. 394 p. K e m p, T. R ., L. P. S t o l t z, J. W. H e r r on and W. T. S m i t h. 1969. H y d r o g en bonding of d a l a p o n. W e ed S c i. 17:444-446. K e y, J. L. 1963. S t u d i es on 2 , 4 -D i n d u c ed c h a n g es in r i b o n u- c l e ic a c id m e t a b o l i sm in e x c i s ed c o rn m e s o c o t yl t i s s u e. W e e ds 1 1 : 1 7 7 - 1 8 1. L u c k w i l l, L. C. and C. P. L l o y d - J o n e s. I960. M e t a b o l i sm of plant g r o w th r e g u l a t o r s. in l e a v es of r ed and of b l a ck c u r r e n t s. Ann. A p p l. B i o. 4 8 : 6 1 3 - 6 2 5. I. 2 , 4 - D i c h l o r o p h e n o x y a c e t ic a c id M e e s, G. C. I960. E x p e r i m e n ts on the h e r b i c i d al a c t i on of 1, 1 - e t h y l e n e - 2 , 21- d i p y r i d y l i um d i b r o m i d e. Ann. appl. B i o l. 4 8 : 6 0 1 - 6 1 2. M o r e l a n d, D E ., W. A. G e n t n e r, J. L. Hilton and K. L. H i l l. 1959. S t u d i es on the m e c h a n i sm of h e r b i c i d al a c t i on of 2 - c h l o r o - 4 , 6 - h is ( e t h y l a m i n o ) - s i - t r i a z i n e. P l a nt P h y s i o l. 3 4 : 4 3 2 - 4 3 5. S a l i s b u r y, F. B. and C. R o s s. 1969. P l a nt P h y s i o l o g y. W a d s- w o r th P u b l. C o ., Inc. B e l m o n t, C a l i f. 747 p. S h i m a b u k u r o, R. H., D. S. F r e a r, H. R. S w a n s on and W. W a l s h. 1970. Glutathione c o n j u g a t i o n: a t r a z i ne r e s i s t a n ce in c o r n. P. 26-27 W e ed S c i. S o c. A m e r. the e n z y m a t ic b a s is f or ( A b s t r .) S h i m a b u k u r o, R. H. and H. R. S w a n s o n. 1969. A t r a z i ne m e t a b- o l i s m, s e l e c t i v i t y, and m o de of a c t i o n. A g r i. F o od C h e m. 1 7 : 1 9 9 - 2 0 5. S l i f e, R. W ., J. L. K e y, S. Y a m a g u c hi and A. S. C r a f t s. 1962. P e n e t r a t i o n, t r a n s l o c a t i o n, and m e t a b o l i sm of 2 , 4 -D and 2 , 4 , 5 -T 2 9 - 3 5. in w i ld and c u l t i v a t ed c u c u m b er p l a n t s. W e e ds 10: S p l i t t s t o e s s e r, W. E. and H. J. Hopen. 1968. The e f f e ct of s i d- u r on on the g r o w th and m e t a b o l i sm of b a r l e y. P. 26-27 W e ed Soc. A m e r. ( A b s t r .) S w a n s o n, C. R. and H. R. S w a n s o n. 1968. M e t a b o l ic f a te of m o n- u r on and d i u r on in i s o l a t ed l e af d i s c s. W e ed S c i. 1 6 : 1 3 7 - 1 4 3. S y n e r h o l m, M. E. and P. W. Z i m m e r m a n. 1947. P r e p a r a t i on of a s e r i es of W - ( 2 , 4 - D) a l i p h a t ic a c i ds and s o me r e l a t ed c o m p o u n ds with a c o n s i d e r a t i on of t h e ir b i o c h e m i c al r o le as plant g r o w th r e g u l a t o r s. C o n t r. B o y ce T h o m p s on Inst. 1 4 : 3 6 9 - 3 8 2. V an O v e r b e e k, J. 1962. P h y s i o l o g i c al r e s p o n s es of plants to h e r b i c i d e s. W e e ds 1 0 : 1 7 0 - 1 7 4. W e s t, S. H., J. B. H a n s on and J. L. K e y. 1960. E f f e ct of 2,4- d i c h l o r o p h e n o x y a c e t ic a c id on the n u c l e ic a c id and p r o t e in content of s e e d l i ng t i s s u e. W e e ds 8:333-340. W e s s e l s, J. S. C. and R. V an D er V e e n. 1956. T he a c t i on of s o me d e r i v a t i v es of p h e n y l - u r e t h an and of 3 - p h e n y l - 1, 1- d i m e t h y l u r ea on the h i ll r e a c t i o n. B i o c h e m. and B i o p h y s. A c ta 1 9 : 5 4 8 - 5 4 9. W h i t e, A ., P. H a n d l er and E. L. Smith. 1968. P r i n c i p l es of b i o c h e m i s t r y. 4th E d. M c G r a w - H i ll B o ok C o. N ew Y o r k. 1 1 87 p. D i s c u s s i on P e r i od D r. W a r d: H a ve you u s ed a m a t e r i al l i ke D M SO to r e d u ce the amount of h e r b i c i de n e e d e d? W h a t 's y o ur thinking on u s i ng s o me m a t e r i al of t h is n a t u re to get b e t t er p e n e t r a t i o n, or m o re r a p id p e n e t r a t i on of h e r b i c i d es into plant t i s s u e. D r. B i n g h a m: My f e e l i ng on D M SO is that w e ' re going to a p r o d- uct that is p r o b a b ly m o re h a z a r d o us than a p a r e nt h e r b i c i d e, and it m ay be m o re of a p r o b l em than u s i ng h i g h er r a t es of h e r b i c i d e s. But going to s u r f a c t a n t s, or s o m e t h i ng that would i n c r e a se the r a te of p e n e t r a t i on and t r a n s l o c a t i o n, n e e ds f u r t h er e m p h a s i s. is an a r ea of r e s e a r ch that D r. S w i t z e r: H i s t o r i c a l l y, h e r b i c i d es f or t u rf h a ve b e en d e v e l- oped p r i m a r i ly by c h e m i c al c o m p a n i e s. T h ey d e v i se a n ew s t r u c- t u re and then t e st it on a g r e at n u m b er of d i f f e r e nt s p e c i e s. E v e n t u a l l y, one is found that w i ll w o rk u s i ng t h is e m p i r i c al a p- p r o a c h. Do you think we a re getting a n y w h e re c l o se to being a b le to d e s i gn a h e r b i c i de f or t u rf w e ed c o n t r o l? Y ou m e n t i o n ed a c o u- p le that a re u s e f ul in the s o u t h e rn g r a s s e s. l i ke to k n ow h ow to d e s i gn one to t a ke b e n t g r a ss out of b l u e g r a s s. Do you think we a re a p p r o x i m a t i ng t h is at a l l? I would I think c h e m i c al c o m p a n i es a re c e r t a i n ly D r. B i n g h a m: at s t r u c t u r e s, and t h ey h a ve b e en o v er the p a st 10 y e a rs or so. T h ey a re t a k i ng a c l o se look at s o me of the h e r b i c i d es w e ' re u s- ing a l r e a d y, t r y i ng to d e s i gn one that would be m o re e f f e c t i ve t h an t h o se we a l r e a dy h a v e. It's e n t i r e ly in the r e a lm of p o s- s i b i l i t y. looking D r. H e m p h i l l: t i o ns in y o ur s t u d i es - - t y p i c al a p p l i c a t i o ns - - w i th a n o r m al e n t ry by a d s o r p t i o n. I a s s u me y ou w e re r e f e r r i ng to f o l i ar a p p l i c a- D r. B i n g h a m: F or the H i ll r e a c t i on s t u d i e s, no. T h e y ' re p r i m- a r i ly t h r o u gh the root s y s t e m. D r. H e m p h i l l: In s o me e l e c t r on m i c r o s c o p ic s t u d i es we found d i f f e r e nt r e a c t i o ns f r om a g i v en c h e m i c al by i n j e c t i n g, as c o n- t r a s t ed to a f o l i ar a p p l i c a t i o n. W h e re is t h is d e g r a d a t i on or a c t i v a t i on o c c u r i n g? in- I think it o c c u rs in m a ny p a r ts of the plant; on the D r. B i n g h a m: w ay to the s i te as w e ll as at the s i te of a c t i o n. I r e a l ly c a n 't a n s- w er y o ur q u e s t i on b e c a u se we h a v e n 't done any w o rk to pinpoint t h e se s i t e s. T h e re h as b e en s o me w o rk at N o r th C a r o l i na State U n i v e r s i t y, w h e re t h ey show a d s o r p t i on of t h e se m a t e r i a ls to p r o- t e in and v a r i o us o t h er c o m p o u n d s. T h is c o u ld t a ke p l a ce a n y- w h e re we w o u ld h a ve the p r o t e i n. I t 's m u ch m o re e f f e c t i ve on p l a nt p r o t e in than it w as on a n i m al p r o t e i n. I w as i n t e r e s t ed in the f a ct that so m a ny of the D r. T i m m o n s: m e t a b o l i sm d e t o x i f i c a t i on m e c h a n i s ms s e em to i n v o l ve oxidation. F or e x a m p l e, you s h o w ed d e m e t h y l a t i on of u r a c i l s, u r e as and h y d r o x y l a t i on of p h e n o xy c o m p o u n d s. T h e se a ll s e em to be o x i- d a t i on m e c h a n i s ms and m ay be c o n t r i b u t i ng to s e l e c t i v i ty of t h e se c o m p o u n d s. One of the m a t e r i a ls that, of c o u r s e, is u s ed with the i n s e c t i c i d es w o n d er if we m i g ht not get quite a d i f f e r e nt s p e c t r um of a c t i v i ty and s e l e c t i v i ty of h e r b i c i d es if t h ey w e re u s ed with s o me of t h e se s y n e r g i s ts to p r e v e nt o x i d a t i on f r om o c c u r i n g? is p i p i r o n yl b u t o x i d e, w h i ch p r e v e n ts o x i d a t i o n. I I don't It sounds l i ke a v e ry good point to m e. D r. B i n g h a m: k n ow if t h e re h as b e en any r e s e a r ch on t h i s. One of the p r i me e f f e c ts w i th the a r s e n i c a ls that is a l w a ys noted, and i t 's in the t e xt b o o k s, is on the p h o s p h o g l y c e r a l d e h y de d e h y d r o g e n a se e n- z y m e. T h is e n z y me c o n t a i ns the SH g r o u p, or s u l f h y d r yl g r o u p. H e re y ou h a ve a r s e n ic a c id r e a c t i ng with t h is s u l f h y d r yl g r o up to g i ve y ou a c o m p l e x. e n z y me i n h i b i t or c o m p l ex showing the e n z y me c o n n e c t ed t h r o u gh a s u l f h y d r yl g r o up to the a r s e n ic g r o u p. T h is t e n ds to r e m o ve t he e n z y me f r om the r e a c t i o n. P o s s i b l y, this is a l i t t le bit d i f- T he f e r e nt f r om w h at y ou h a ve h e a rd as one of the m e c h a n i s m s. r e a c t i ve s i te on the e n z y me is the s u l f h y d r yl g r o up w h i ch r e a c ts w i th the s u b s t r a te ( 3 - p h o s p h o g l y c e r a l d e h y d e) to f o rm the e n z y m e- s u b s t r a te c o m p l e x. g l y c e r ic a c i d, it p r o d u c es r e d u c ed t r i p h o s p h o p y r i d i ne n u c l e o t i d e, the p l a n ts s o u r ce of e n e r g y. In the p r o c e ss of c o n v e r s i on to the p h o s p h o- If a r s e n ic c o m p l e x es with the s u b- In o t h er w o r d s, you get a s u b s t r a te or an s t r a t e, it is c o n v e r t ed to p h o s p h o g l y c e r ic a c id and b y p a s s es the A TP p r o d u c t i on that n o r m a l ly o c c u rs f r om o x i d a t i on of p y r i d i ne n u c l e o t i d e s. H ow is r e s i s t a n ce or s u s c e p t a b i l i ty r e l a t e d? T h is h a s nft b e en e x p l a i n ed v e ry w e ll with t h e se h e r b i c i d e s, e x c e pt a b s o r p t i on or p e n e t r a t i on and t r a n s l o c a t i on in the amount that t h is r e a c t i on is d e p e n d ed on in the plant. C o n v e r s i on of the a r s e n i c al to a r s e n ic a c id m ay a l so be at d i f f e r e nt r a t es in v a r i o us p l a n t s. It is v e ry m o b i le o n ce it is c o n v e r t e d. We do k n ow that a r s e n ic w i ll r e a ct w i th m a ny o t h er e n z y m es that h a ve t h is a c t i ve SH s i te and c a u se r e d u c ed r a t es of e n z y me a c t i o n. of the m a j or s i t es of a c t i on of a r s e n ic a c i d. It s e e ms to be one h e r b i c i de E F F E C TS OF H E R B I C I D ES ON P L A NT P H Y S I O L O G I C AL P R O C E S S ES D o n a ld E. D a v i s* D e p a r t m e nt of B o t a ny and P l a nt P a t h o l o gy A u b u rn U n i v e r s i ty A u b u r n, A l a b a ma 36830 I n t r o d u c t i on T h e re a re 50 to 100 h e r b i c i d es c o m m o n ly u s ed in the U. S. t o d a y. T he a c t u al n u m b er is dependent on how one d e f i n es " c o m- m on u s e ." E a ch of t h e se h e r b i c i d es h as at l e a st a s l i g h t ly d i f f e r- ent e f f e ct on the p h y s i o l o g i c al p r o c e s s es of the plant. It s e e ms l i k e ly that s e v e r al h e r b i c i d es h a ve m o re than one s i te of a c t i o n. F u r t h e r m o r e, the e x a ct r e s p o n se e l i c i t ed m ay be i n f l u e n c ed by s e v e r al d i f f e r e nt f a c t o r s. F or e x a m p l e, 2 , 4 -D m ay s t i m u l a t e, inhibit or h a ve no e f f e ct on the r a te of r e s p i r a t i o n, depending on the kind of plant t r e a t e d, the d o s a ge u s e d, the t r e a t m e nt w h en the m e a s u r e m e nt of the plant and the plant o r g an on w h i ch the m e a s u r e m e nt is m a d e. is m a d e, the p h y s i o l o g i c al a ge l e n g th of t i me a f t er T he h e r b i c i d es to be c o n s i d e r ed a re l i s t ed in T a b le 1 along w i th i n f o r m a t i on of g e n e r al i n t e r e st about t h e m. T h e se h e r b i c i d es a re c l a s s i f i ed a c c o r d i ng to t h e ir a p p a r e nt p r i m a ry m o de of a c- tion in T a b le 2. It should be noted that the p r i m a ry m o de of a c- t i on h as not b e en f u l ly e s t a b l i s h ed f or s o me of t h e se h e r b i c i d e s. F u r t h e r m o r e, t h e re a re a l w a ys p r o b l e ms a s s o c i a t ed with t r y i ng to l u mp d i f f e r e nt t h i n gs into g r o u p s, w h e t h er the things being c l a s s i f i ed a re plant s p e c i e s, r o c ks or o r g a n ic c h e m i c a l s. a l w a ys s e em to be s o me i n d i v i d u a ls that don't f it any c a t e g o ry w h i le o t h e rs h a ve c h a r a c t e r i s t i cs that f it into m o re than one c a t- e g o r y. T h e re * D r. D a v i s1 p a p er w as p r e s e n t ed by D r. R ay D i c k e ns of A u b u rn U n i v e r s i t y. T a b le 1. A l p h a b e t i c al l i st of s o me t u r f g r a ss h e r b i c i d es with the c h e m i c al n a me in b r a c k e t s. T he i n f o r m a t i on p r o v i d ed o p p o s i te e a ch l e t t er is: A - s o me t r a de n a m es and m a n u f a c t u r e r s, B - f a m- i ly of h e r b i c i d e, C - t y pe of m o de of a c t i o n, D - s o me of the r e c o m- m e n d ed u s e s, and E - a c u te o r al t o x i c i ty to r a t s j î :/ 1. A t r a z i ne [ 2 - c h l o r o - 4 ( e t h y l a m i n o) - 6 - ( i s o p r o p y l a m i n o ) - ^- t r i a z i n e] . A. B. C. D. E. A A t r e x, G e s a p r im - G e i gy A g r i c u l t u r al C h e m i c a l s. j S - t r i a z i n e. P h o t o s y n t h e t ic P r e - e m e r g e n ce c o n t r ol of c r a b g r a s s, g o o s e g r a ss and m o st b r o a d l e af w e e ks in e s t a b l i s h ed t u r f. LD 50 - 3080 m g / kg f or r a t s. i n h i b i t o r. | ^ - b u t y l - N - e t h y l --a , a , a , t r i f l u o r o - 2 - 6 - d i n i t r o - £ - t o l- 2. B e n e f in uidine 3. A. B. C. M i t o t ic i n h i b o t o r? A f f e c ts s e ed g e r m i n a t i on and root B a l an - E l a n co P r o d u c ts C o. T o l u i d i n e. g r o w t h. P r e - e m e r g e n ce c o n t r ol of annual g r a s s es t u r f. LD 50 -> 10,000 m g / kg f or r a t s. D. E. in e s t a b l i s h ed 3. B e n s u l i de [ 0 , 0 - d i i s o p r o p yl p h o s p h o r o d i t h i o a t e - S - e s t er with N - ( 2 - m e r c a p t o e t h y l) b e n z e ne s u l f o n a m i de ]]. A. B e t a s an - S t a u f f er C h e m i c al C o. a n d P r e - s a n - M a l l i n- c k r o dt C o. A m i d e s. C e ll d i v i s i on i n h i b i t o r? A f f e c ts s e ed g e r m i n a t i on and r o ot g r o w t h. P r e - e m e r g e n ce c o n t r ol of annual b l u e g r a ss and s u m m er a n n u al g r a s s es LD 50 - 770 m g / kg f or r a t s. in e s t a b l i s h ed t u r f. B. C. D. E. 4. C a c o d y l ic a c id [ h y d r o x y d i m e t h y l a r s i ne o x i d e ]. P h y t ar 138 - A n s ul C o. A. B. O r g a n ic a r s e n i c. C. R e s p i r a t i on D. K i l ls a ll g r a ss p l a n ts f or sod r e n o v a t i on and spot t r e a t- i n h i b i t o r? m e n t. LD 50 - 830 m g / kg f or r a t s. E. 5. CMA^Calcium methanearsonate 3« V a r i o us - V i n e l a n d. A. B. O r g a n ic a r s e n i c. C. R e s p i r a t i on D. i n h i b i t o r? C o n t r ol s a n d b ur and o t h er annual g r a s s es in e s t a b l i s h ed b e r m u d a g r a ss and c e r t a in o t h er t u r f. LD 50 - 1000-2000 m g / kg f or r a t s. e s t i m a t e. No p u b l i s h ed v a l ue w as found). ( T h is v a l ue is an E. 6. D a l a p on [ 2 , 2 - d i c h l o r o p r o p i o n ic a c i d ^. A. D o w p on ( s o d i um salt) - D ow C h e m i c al C o. and R a d a p o n- C h e m a g ro C o. B. H a l o g e n a t ed a l i p h a t ic a c i d. C. G r o w th r e g u l a t or ( 2 , 4 - D ) - t y pe e f f e c ts and o t h e r s. D. K i l ls a ll g r a s sy p l a n ts f or sod r e n o v a t i on and spot t r e a t- m e n t. LD 50 - 7500 to 9500 m g / kg f or r a t s. E. 7. D C PA [ d i m e t h yl t e t r a c h l o r o t e r e p h t h a l a te ] . A. D a c t h al - D i a m o nd S h a m r o ck C o. B. C. P h t h a l ic a c i d s. C e ll d i v i s i on i n h i b i t o r? A f f e c ts s e ed g e r m i n a t i on and r o ot g r o w t h. P r e - e m e r g e n ce w e ed c o n t r ol of c r a b g r a ss and o t h er a n n u al g r a s s es LD 50 ->3000 m g / kg f or r a t s. in e s t a b l i s h ed t u r f. D. E. 8. D i c a m ba [ 3 , 6 - d i c h l o r o - O - a n i s ic a c i d ]. - V e l s i c ol C h e m i c al A. B a n v el D ( d i m e t h y l a m i ne salt) C o r p. B e n z o ic a c i d. B. C. G r o w th r e g u l a t or ( 2 , 4 - D ) - t y pe e f f e c t s. D. P o s t e m e r g e n ce w e ed c o n t r ol of henbit, c h i c k w e ed and o t h er annual b r o a d l e af w e e ds in e s t a b l i s h ed t u r f. LD 50 -> 1000 m g / kg f or r a t s. E. 9. D S MA [ d i s o d i um m e t h a n e a r s o n a te ]. A. A n s ar 184 - A n s ul C o. and o t h er m a n u f a c t u r e rs and t r a de n a m e s. B. O r g a n ic a r s e n i c. C. R e s p i r a t i on D. i n h i b i t o r? P o s t e m e r g e n ce w e ed c o n t r ol of c r a b g r a s s, d a l l i s g r a s s, b a h i a g r a s s, n u t g r a ss and j o h n s o n g r a ss in b e r m u d a g r a ss and z o y s i a g r a s s. Do not u se in c e n t i p e d e, or St. A u g u s- t i n e, and e x c e pt at l ow r a t es in T i f g r e en b e r m u d a g r a s s. LD 50 - 2800 m g / kg f or r a t s. E. 10. M A M A [ M o n a m m o n i um m e t h a ne a r s o n a t e ^. A. A n s ar 157 - A n s ul C o. and v a r i o us o t h er m a n u f a c t u r e rs and t r a de n a m e s. B. O r g a n ic a r s e n i c. C. R e s p i r a t i on D. P o s t e m e r g e n ce w e ed c o n t r ol of c r a b g r a s s, d a l l i s g r a s s, n u t g r a ss and j o h n s o n g r a ss in e s t a b l i s h ed b e r m u d a g r a ss and z o y s i a g r a s s. Do not u se in c e n t i p e de or St. A u g u s- t i n e. LD 50 - 750 m g / kg f or r a t s. i n h i b i t o r? E. 11. M S MA [ M o n o s o d i um m e t h a n e a r s o n a te 3. A. A n s ar 170 - A n s ul C o. and v a r i o us o t h er c o m p a n i es and t r a de n a m e s. B. O r g a n ic a r s e n i c. C. R e s p i r a t i on i n h i b i t o r? D. E. P o s t e m e r g e n ce c o n t r ol of d a l l i s g r a s s, c r a b g r a ss s o n g r a s s, s a n d b u r, b a h i a g r a ss and n u t g r a ss in e s t a b- l i s h ed t u r f. Do not u se in c e n t i p e de or St. A u g u s t i n e. LD 50 - 1800 m g / kg f or r a t s. j o h n- 12. P a r a q u at [ l , l!- d i m e t h y l - 4 , 4,- b i p y r i d i n i um i o n 3- A. O r t ho P a r a q u at - C h e v r on C h e m i c al C o. B. C. B i p y r i d i n i um q u a r t e r n a ry s a l t s. F r ee r a d i c al f o r m a t i on in the light g e n e r a t i ng o t h er t o x ic f r ee r a d i c a ls that inhibit s u l f h y d r yl e n z y m e s. P o s t e m e r g e n ce c o n t r ol of w i n t er a n n u a ls in d o r m a nt t u r f. LD 50 - 150 m g / kg f or r a t s. D. E. A. B. C. D. 13. S i d u r on [ l , ( 2 - m e t h y l c y c l o h e x y l ) - 3 - p h e n y l u r e a] . T u p e r s an - E. I. duPont de N e m o u rs and C o. P h e n y l u r e a. C e ll d i v i s i on i n h i b i t o r? A f f e c ts r o ot g r o w t h. P r e - e m e r g e n ce c o n t r ol of annual g r a s s es t u rf of b l u e g r a s s, b e n t g r a s s, z o y s ia and f e s c u e. LD 50 -> 5000 m g / kg f or r a t s. E. in e s t a b l i s h ed 14. S i l v ex f 2 - ( 2 , 4 , 5 - t r i c h l o r o p h e n o x y) p r o p i o n ic a c i d ]. A. K u r on ( p r o p y l e ne g l y c ol b u t yl e t h er e s t e r s) - D ow C h e m i c al C o. C h l o r o p h e n o x y. B. C. G r o w th r e g u l a t or ( 2 , 4 - D ) - t y pe e f f e c t s. D. C o n t r ol b r o a d l e af w e e ds including b u r k h o rn p l a n t a i n, c o m m on c h i c k w e e d, d a n d e l i o n, e t c. in e s t a b l i s h ed t u r f. Do not u se in St. A u g u s t i ne or c e n t i p e d e. LD 50 - 650 m g / kg f or r a t s. E. 15. S i m a z i ne [ 2 - c h l o r o - 4 , 6 - b i s ( e t h y l a m i n o) - s - t r i a z i ne ] . A. B. C. P r i n c ep - G e i gy A g r i c u l t u r al C h e m i c a l s. ^S-triazine. P h o t o s y n t h e t ic i n h i b i t o r. D. E. P r e - e m e r g e n ce c o n t r ol of c r a b g r a s s, g o o s e g r a ss and m o st b r o a d l e af w e e ds in a f ew t u r f g r a s s e s. LD 50 - 2000 m g / kg f or r a t s. 1 6. T e r b u t ol [ 2 , 6 - d i - t e r t - b u t y l - p - t o l yl m e t h y l c a r b a m a t e] . A. B. C. D. E. A z ak - H e r c u l es Inc. C a r b a m a t e. C e ll d i v i s i on i n h i b i t o r. A f f e c ts s e ed g e r m i n a t i on and r o ot g r o w t h. P r e - e m e r g e n ce w e ed c o n t r ol of annual g r a s s es e s t a b l i s h ed t u r f. LD 50 - 300-1000 m g / kg f or r a t s. in 1 7. 2 , 4 -D [ ( 2 , 4 - d i c h l o r o p h e n o x y) a c e t ic acid|[. C h l o r o p h e n o x y. A. N u m e r o us t r a de n a m e s, f o r m u l a t i o n s, and f o r m u l a t o r s. B. C. G r o w th r e g u l a t or ( 2 , 4 - D ) - t y pe e f f e c t s. D. C o n t r ol b r o a d l e a v ed w e e ds in e s t a b l i s h ed t u r f. Do not u se in c e n t i p e de or St. A u g u s t i n e. LD 50 - 300-1000 m g / kg f or r a t s. E. 18. 2 , 4 , 5 -T [ ( 2 , 4 , 5 - t r i c h l o r o p h e n o x y) a c e t ic a c id ]. C h l o r o p h e n o x y. A. N u m e r o us t r a de n a m e s, f o r m u l a t i o n s, and f o r m u l a t o r s. B. C. G r o w th r e g u l a t or ( 2 , 4 - D ) - t y pe e f f e c t s. D. C o n t r ol c e r t a in 2 , 4 - D - r e s i s t a nt b r o a d l e a v ed w e e ds e s t a b l i s h ed t u r f. Do not u se in c e n t i p e de or St. A u g u s t i n e. LD 50 - 300 m g / kg f or r a t s. E. in a / —' D a ta s u p p l i ed in this t a b le is to s u p p ly g e n e r al i n f o r m a t i on and is not i n t e n d ed as a b a s is f or r e c o m m e n d a t i o ns f or u s e. T a b le 2. A c l a s s i f i c a t i on of s o me c o m m on t u r f g r a ss h e r b i c i d es a c c o r d i ng to t h e ir p r o b a b le p r i m a ry m o de of a c t i o n. T y pe of A c t i on H e r b i c i de A. Inhibit p h o t o s y n t h e s is a t r a z i n e, s i m a z i ne B. Inhibit r e s p i r a t i on C M A, D S M A, M A M A, M S MA C. Inhibit c e ll d i v i s i on b e n e f i n, b e n s u l i d e, D C PA s i d u r o n, t e r b u t ol D. E. D i s t u rb h o r m o n al g r o w th r e g u l a t i on d a l a p o n, s i l v e x, 2 , 4 - D, 2 , 4 , 5 - T, d i c a m ba P r o d u ce f r ee r a d i c a ls that i n a c t i v a te s u l f h y d r yl e n z y m es p a r a q u at ^J T he m o de of a c t i on h as not b e en f u l ly e s t a b l i s h ed f or s o me of t h e se c h e m i c a l s. T h e se h a ve b e en p l a c ed into c a t e g o r- i es w i th o t h er h e r b i c i d es h a v i ng s i m i l ar e f f e c ts and f or w h i ch the m o de of a c t i on is known. P h o t o s y n t h e s is Inhibition D e s c r i b ed in the v e ry s i m p l e st t e r m s, p h o t o s y n t h e s is is the p r o c e ss by w h i ch g r e en p l a n ts m a ke food and e v o l ve o x y g en w h i le u s i ng c a r b on d i o x i d e, w a t er and light e n e r g y. that a plant t r e a t ed w i th a p h o t o s y n t h e s is i n h i b i t or would die of s t a r v a t i o n, and that the l e n g th of t i me r e q u i r ed to k i ll the plant w o u ld d e p e nd on the s i ze of i ts food r e s e r v es and h ow f a st it w as u s i ng t h e m. P l a n ts k i l l ed by p h o t o s y n t h e s is i n h i b i t o rs do not f u l ly m a t ch t h e se e x p e c t a t i o n s. T h e r e f o r e, it is n e c e s s a ry to c o n- s i d er p h o t o s y n t h e s is and the a c t i on of p h o t o s y n t h e s is i n h i b i t o rs in s o m e w h at g r e a t er d e t a i l. It would be e x p e c t ed T he c o m p l ex s e r i es of b i o c h e m i c al p r o c e s s es g r o u p ed t o- g e t h er and c a l l ed p h o t o s y n t h e s is c an be s u b d i v i d ed into two c a t- e g o r i e s, depending on w h e t h er or not the p r o c e s s es l i g h t. T h e se that r e q u i re l i g ht a re f u r t h er s u b d i v i d ed into two c a t e g o r i es w h i ch w i ll be d i s c u s s ed l a t e r. A r n on (I960) h as s u m- m a r i z ed h is r e s e a r ch and that of o t h e rs on the light r e a c t i on of p h o t o s y n t h e s is in an e a s i ly u n d e r s t a n d a b le a r t i c le p u b l i s h ed in the S c i e n t i f ic A m e r i c a n. S o me c h a n g es h a ve b e en m a de in h is s t o ry of p h o t o s y n t h e s is s i n ce that t i me but t h ey w i ll not s i g n i f i- c a n t ly a f f e ct o ur c o n s i d e r a t i on of the p r o c e ss ( F o g g, 1968; L.e- v i n e, 1969). r e q u i re T he d a rk r e a c t i on of p h o t o s y n t h e s is u s es A TP (adenosine t r i p h o s p h a t e ), N A D PH ( r e d u c ed n i c o t i n o m i de adenine d i n u c l e o- t i de phosphate) and CC>2 r e s u l t i ng in the f o r m a t i on of c a r b o h y- d r a t e s. T he c a r b on of CC>2 is thus s a id to be f i x e d. T h e se d a rk r e a c t i o ns a re not l i m i t ed to g r e en p l a n t s, but the g r e at bulk of a ll c a r b on f i x a t i on o c c u rs in the c h l o r o p l a st and u s es A TP and N A D PH p r o d u c ed by the c h l o r o p l a st in the light. W h en p l a n ts a re t r e a t ed with p h o t o s y n t h e s is i n h i b i t o r s, the amount of c a r b on f i x ed c an be r e d u c ed to the a m o u nt that c an be f i x ed in the d a r k, but the p r o c e ss It is a p p a r e nt that t h e se h e r b i c i d es d i r e c t ly a f f e ct only the c a r b o h y d r a te s y n t h e s is d e p e n d e nt on A TP and N A D PH p r o d u c ed by the c h l o r o p l a st the is n e v er c o m p l e t e ly stopped. l i g h t. in W h en light s t r i k es a g r e en plant it m ay be a b s o r b ed by the g r e en p i g m e n t, c h l o r o p h y l l, l o c a t ed in b o d i es c a l l ed c h l o r o p l a s t s. C h l o r o p h y ll in the c h l o r o p l a st is bound to p r o t e in m e m b r a n es and a r r a n g ed in thin, n e a r ly round, s h e e ts w h i ch in turf o c c ur s t a c k s; t h e se p a c k e ts a re c a l l ed g r a n a. A p p a r e n t l y, in the o r d er of 2,500 c h l o r o p h y ll m o l e c u l es f u n c t i on t o g e t h er as a unit in c a p t u r i ng the l i g ht e n e r gy u s ed in p h o t o s y n t h e s i s. When a p r o t on of l i g ht is a b s o r b e d, its e n e r gy is t r a n s m i t t ed to an e l e c t r o n; the e l e c t r on is e j e c t ed and the c h l o r o p h y ll b e c o m es o x i d i z e d. in Upon e j e c t i o n, t h is h i g h ly e n e r g e t ic e l e c t r on c an e n t er In c y c l ic p h o t o p h o s p h o r y l a t i o n, the e l e c t r on e i t h er of two b i o l o g i c al p a t h w a y s, c y c l in or n o n - c y c l in p h o t o- p h o s p h o r y l a t i o n. is c a p t u r ed by an e l e c t r on a c c e p t or and p a s s ed along a c h e m- i c al p a t h w ay that i n c l u d es the c y t o c h r o m e s. E v e n t u a l ly it r e- t u r ns to c h l o r o p h y l l. Thi.s e x p l a i ns w hy the p r o c e ss is c a l l ed c y c l ic and the c h l o r o p h y ll d o es not b e c o me m o re and m o re h i g h ly o x i d i z ed as light is a b s o r b ed and e l e c t r o ns e j e c t e d. As the e l e c t r on t r a v e ls t h is c h e m i c al p a t h w ay it g i v es up m e n ts of e n e r gy that c an be u s ed in the c o n v e r s i on of A DP ( a d e n o s i ne diphosphate) to A T P. T en y e a rs a go it w as g e n e r- a l ly a s s u m ed that s u ch a c o n v e r s i on o n ly o c c u r r ed in the m i t- o c h o n d r i o n. i n c r e- In n o n - c y c l ic p h o t o p h o s p h o r y l a t i o n, the e j e c t ed is c a p t u r ed and p a s s ed along a c h e m i c al p a t h w ay to a c o m p o u nd that l e a ds to the s p l i t t i ng of w a t er w h i ch f u r n i s h es the p r o t on f or the f o r- m a t i on of N A D PH f r om N A D P. H y d r o x yl ions (OH) r e s u l t i ng f r om t h is p r o c e ss c o m b i ne to f o rm w a t er and o x y g en and the e x t ra e l e c t r on a g a in p a s s es along a c h e m i c al p a t h w a y, including c y t o c h r o m e s, b a ck to c h l o r o p h y l l. D u r i ng the p a s s a ge along the e l e c t r on t r a n s f er c h a i n, e n e r gy is g i v en up and A DP is c o n- v e r t ed to A T P. r e l e a s ed and A TP and N A D P H, w h i ch m ay be u s ed in c a r b on f i x a t i o n, a re In n o n c y c l ic p h o t o p h o s p h o r y l a t i o n, o x y g en is f o r m e d. P h o t o s y n t h e s is i n h i b i t o rs b l o ck n o n - c y c l ic p h o t o p h o s p h o r y- l a t i on at s o me point p r i or to the splitting of w a t er ( C o o k, 1956; V an O v e r b e c k, 1962; W e s s e ls and v an d er V e e n, 1956). G o od ( 1 9 6 1, 1962) h as r e v i e w ed the w o rk of o t h e rs and i n c l u d ed m u ch a d d i t i o n al w o rk of h is own in two p a p e rs on the p h o t o s y n t h e s is i n h i b i t o r s. He l i s ts m a ny d i f f e r e nt h e r b i c i d es that a re i n h i b i- t o rs and c a l c u l a t es the c o n c e n t r a t i o ns of e a ch n e c e s s a ry to b r i ng about a 50% inhibition. T he p a rt of p h o t o s y n t h e s is i n v o l- v i ng the splitting of w a t er is c a l l ed the H i ll r e a c t i o n, and s p e- c i al t e c h n i q u es m a ke p o s s i b le d i r e ct in v i t ro m e a s u r e m e n ts of t h is p r o c e ss with c h l o r o p l a s ts i s o l a t ed f r om plant t i s s u e s. Good (1961) c o n c l u d es that inhibition of the H i ll r e a c t i on is a p p a r e n t ly the p r i m a ry m o de of a c t i on of the a n i l i d es (which i n c l u de p h e n y l u r e a s ), the a l k y l a m i d es and the . s - t r i a z i n e s. A t r a z i ne and s i m a z i ne in o ur l i st of t u rf h e r b i c i d es a re s^-triazines. A s h t on (1965) h as g i v en s o me m o re r e c e nt i n f o r m a t i on on p h o t o s y n t h e s is i n h i b i t o r s. the M a ny f i e ld and l a b o r a t o ry o b s e r v a t i o ns c o n f i rm the a n t i c i- i n h i b i t o rs p a t ed r e s u l ts of s u ch inhibition. T he p h o t o s y n t h e s is c. re m o re e f f e c t i ve in high than in l ow l i g ht i n t e n s i ty and a re i n- e f f e c t i ve in the d a r k. T h ey show m a x i m um e f f e ct as light w a ve l e n g t hs m a t c h i ng the a b s o r p t i on s p e c t r um of c h l o r o p h y l, and t h ey a re o f t en not e f f e c t i ve a g a i n st n o n - g r e en t i s s u e. g r e a t ly d e c r e a se c a r b on f i x a t i on and stop o x y g en evolution. The c h l o r o p h y ll in t r e a t ed p l a n ts b e c o m es o x i d i z e d. Supplying an o x i d i z a b le s u b s t r a te f r om an e x t e r n al s o u r ce g i v es s o me p r o- t e c t i o n. O n ly one o b s e r v a t i on d o es not s e em to fit. S e n s i t i ve p l a n ts t r e a t ed with t h e se c o m p o u n ds die m u ch q u i c k er than if t h ey w e re not t r e a t ed and p l a c ed in the d a rk to stop a ll t h e s i s. T h is o b s e r v a t i on l ed S w e e t z er and Todd (1961) to p o s- t u l a te the f o r m a t i on of a p h y t o t o x ic m a t e r i al as a r e s u lt of this b l o c k. T h ey p h o t o s y n- T he p h o t o s y n t h e s is i n h i b i t o rs a re m o st o f t en u s ed as p r e- e m e r g e n ce h e r b i c i d e s. T h ey a re a p p l i ed to the s o il and k i ll the s e e d l i ng o n ly a f t er the c h e m i c al h as b e en a b s o r b ed by the r o o ts and the plant h as e m e r g ed f r om the s o i l. F a i l u re to get good k i ll of s e n s i t i ve s p e c i es u s u a l ly m e a ns that the c h e m i c al did not e n t er the r o o t s; n o r m a l ly due to (1) l a ck of u n i f o rm a p p l i c a t i o n, (2) l a ck of r a in to l e a c h - t he c h e m i c al into the s o il or (3) g e r m i n- a t i on of the s e ed at a depth b e l ow the t r e a t ed s o il l a y e r. R e s p i r a t i on Inhibition T h is p r e s e n t a t i on w i ll be l i m i t ed to t h o se p r o c e s s es that in o c c u rs in the m i t o c h o n d r ia (tiny o r g a n e l l es i n s i de e a ch c e l l) w h i ch A DP is c o n v e r t ed to A T P, 02 is c o n s u m e d, C 02 and w a t er a re p r o d u c e d, and an e n e r gy s o u r ce is o x i d i z e d. E f f e c ts of h e r- b i c i d es on r e s p i r a t i on a re u s u a l ly m e a s u r ed in one of two w a y s. in F i r s t, O2 c o n s u m p t i on m ay be f o l l o w ed as p r e s s u re c h a n g es a c l o s ed s y s t em in w h i ch the C O2 p r o d u c ed is r e m o v ed by a s u i t a b le a b s o r b a n t. T he p r e s s u re c h a n g es c an be c o n v e r t ed to the a m o u n ts of O2 u s ed by u t i l i z i ng s u i t a b le c o n s t a n t s. o t h er s y s t e m, d i s a p p e a r a n ce of O2 f r om s o l u t i on is f o l l o w ed p o l a r o g r a p h i c a l ly by m e a ns of an o x y g e n - s e n s i t i ve e l e c t r o d e. T he r e a d i n gs obtained m ay a l so be c o n v e r t ed to a m o u n ts of O2 u s e d. M e a s u r e m e n ts a re m a de e i t h er on s e e d s, v e ry s m a ll p l a n t s, p o r t i o ns of p l a n ts or m i t o c h o n d r ia i s o l a t ed f r om plants. L o t l i k a r, R e m m e rt and F r e ed ( 1968) h a ve r e p o r t ed the e f f e c ts of 22 h e r b i c i d es on the r e s p i r a t i on of m i t o c h o n d r ia i s o l a t ed f r om c a b b a g e. In the It is o f t en s a id that A TP is the u n i v e r s al When r e s p i r a t i on i n h i b i t o rs a re a p p l i ed to a plant t h e re m ay or m ay not be an i m m e d i a te d e c r e a se in O2 c o n s u m p t i o n. O f t e n, t h e re is an i n i t i al i n c r e a se in O2 u p t a k e. T he plant is not d i r e c t- ly dependent on O2 c o n s u m p t i on p er s e, but r a t h er on the c o n v e r- s i on of A DP to A T P. c u r r e n cy that is c a l l ed upon by a ll c e l l s, both plant and a n i m a l, to d r i ve e n e r gy c o n s u m i ng p r o c e s s e s. T wo of the m o re potent r e s p i r a t i on i n h i b i t o r s, p e n t a c h l o r o p h e n ol and d i n o s eb ( D N B P ), a re e f f e c t i ve b e c a u se t h ey u n c o u p le o x i d a t i ve p h o s p h o r y l a t i o n. In s i m p le t e r ms t h is m e a ns 02 is c o n s u m ed and s u b s t r a te o x i- d i z ed but the e n e r gy r e l e a s ed is not u s ed in c o n v e r t i ng A DP to A T P. B e c a u se of the i m p o r t a n ce of t h is p o s s i b i l i t y, a t h o r o u gh i n v e s t i g a t or w i ll d e t e r m i ne both the o x y g en c o n s u m ed and the amount of i n o r g a n ic p h o s p h o r o us u s ed in c o n v e r t i ng A DP to A T P. T he r e s u l ts a re u s u a l ly e x p r e s s ed as a r a t io b e t w e en t h e se ( P :0 r a t i o ), and a d e c r e a se in the P :0 r a t i on is c o n s i d e r ed to be e v i- dent of uncoupling. T he i d e al r a t io w h en m a l a te or c i t r a te o x i d i z ed is 3.0. is R e s p i r a t i on i n h i b i t o rs c a u se v e ry r a p id k i l l i n g. Without A T P, a ll l i fe p r o c e s s es stop. T he n e ed f or A TP is c o m m on to both p l a n ts and a n i m a l s. C o n s e q u e n t l y, h e r b i c i d es that a re r e s- p i r a t i on i n h i b i t o rs a re o f t en quite t o x ic to m a n. R e s p i r a t i on i n- h i b i t o rs a re u s u a l ly a p p l i ed as f o l i a ge s p r a y s, c a u s i ng contact k i l l. T he f o l i a g e - a p p l i ed r e s p i r a t i on inhibiting h e r b i c i d es w i ll u s u a l ly not t r a n s l o c a te to the r o o ts s i n ce t h ey a l so t he p h l o em t r a n s p o rt s y s t e m. i n a c t i v a te A r s e n a te and a r s e n i te a re known to i n t e r f e re with m i t o- c h o n d r i al m e t a b o l i s m. T he p r i m a ry m o de of a c t i on of the o r- g a n ic a r s e n ic c o m p o u n ds is p r o b a b ly t h r o u gh inhibition of r e s- p i r a t i o n, a l t h o u gh I am not a w a re of any s u f f i c i e n t ly d e f i n i te s t u dy to c o n f i rm t h is p r o p o s a l. It should be m e n t i o n ed that s o me of the o r g a n ic a r s e n i cs h a ve a r e l a t i v e ly l ow t o x o c i ty to m a m m a l s. Inhibition of C e ll D i v i s i on a f e r t i l i z ed egg and c e ll d i f f e r e n- l e a st A ll h i g h er p l a n ts s t a rt t h e ir l i fe h i s t o ry as and s u b s e q u e nt c e ll d i v i s i o n, c e ll e n l a r g m e nt t i a t i on r e s u lt in an e m b r yo in the s e e d. O f t e n, t h e re is at a s h o rt p e r i od w h en c e ll d i v i s i on s t o ps w h i le the s e ed is d o r m a n t. W h en the s e ed g e r m i n a t e s, c e ll d i v i s i on s t a r ts a g a in but it is p r i- m a r i ly l i m i t ed to c e r t a in a r e as c a l l ed m e r i s t e m s. ( b r o a d l e a v ed p l a n t s ), t h e se o c c ur at o p p o s i te ends of the e m b r y- o n ic a x i s; one being the r o ot t i ps or r a d i c le and the o t h er the s t em tip or p l u m u l e. An u n d e r s t a n d i ng of the l o c a t i on of t h e se m e r i s t e ms i n h i b i t o rs of c e ll d i v i s i on f u n c t i o n. is n e c e s s a ry to the u n d e r s t a n d i ng of how In d i c o ts h as e m e r g ed and T h e re a re two t y p es of g e r m i n a t i on in d i c o t s. F i r s t, we w i ll c o n s i d er the kind of g e r m i n a t i on that o c c u rs in cotton or k i d n ey b e a ns ( F i g. 1 and 2). T he young r o ot e m e r g es f r om the s e ed in t h e se p l a n t s. E x i s t i ng c e l ls e l o n g a te as n ew o n es a re b e i ng f o r m ed in the r o ot tip. A f t er the r o ot a n c h o r ed the s e e d, the h y p o c o t yl b e g i ns to e l o n g a t e. out in the f o rm of a c r o ok and, as it e l o n g a t e s, it d r a gs the s e ed c o at and c o t y l e d o ns out of the g r o u n d. When light s t r i k es the h y p o c o t y l, the hook b e g i ns to s t r a i g h t e n, the c o t y l e d o ns e x- pand and the old s e ed c o at s p l i ts and f a l ls off. T he g r o w th of the h y p o c o t yl is m o s t ly due to c e ll e n l a r g e m e nt of p r e - e x i s t i ng c e l l s. p l u m u le b e g i ns r a p id c e ll d i v i s i on and g r o w t h. W h i le the s e ed w as in the g r o u nd the p l u m u le w as n e s t l ed b e t w e en the two c o t y l e d o n s, p a r t i a l ly c o v e r ed by a r e l a t i v e ly i m p e r m e a b le s e ed c o a t. It is only a f t er the c o t y l e d o ns s t a rt to expand that the It g r o ws In s o me d i c o t s, s u ch as E n g l i sh p e a s, the h y p o c o t yl d o es not e l o n g a te ( F i g. 3). T he old s e ed and c o t y l e d o ns r e m a in in the g r o u n d. G r o w th of the p l u m u le and e p i c o t yl r e s u lt in the F i g u re 1 F i g u re 2 plumule F i g u re 3 F i g u re 4 e m e r g e n ce of the s e e d l i n g. S o m e t i m es t h is e p i c o ty is a l so h o o k ed in a f a s h i on s i m i l ar to that of the h y p o c o t yl of the k i d n ey b e an and cotton. T he g e r m i n a t i on of c o rn and o t h er g r a s s es ( m o n o c o t s) is c o n s i d e r a b ly d i f f e r e nt f r om that of d i c o ts ( F i g. 4). M o n o c o ts h a ve only one c o t y l e d o n, and it a l w a ys r e m a i ns within the s e ed in the ground. T he p l u m u le is c o v e r ed by a s h e a th of t i s s ue c a l l ed the c o l e o p t i l e. G r a s s es and o t h er m o n o c o ts a l so h a ve t wo a d d i t i o n al m e r i s t e ms that a re not p r e s e nt in d i c o t s. One is l o c a t ed i m m e d i a t e ly b e l ow the a t t a c h m e nt of the c o l e o p t i le and r e s u l ts in the e l o n g a t i on of the s t em u n d e r n e a th it c a l l ed t he m e s o c o t y l. T he o t h er is l o c a t ed i m m e d i a t e ly a b o ve the a t- t a c h m e nt of the c o l e o p t i l e, and it r e s u l ts in the e l o n g a t i on of t he node i m m e d i a t e ly a b o ve it. A c t u a l l y, t h e re is one of t h e se m e r i s t e ms f or e a ch node of the s t e m. W h en g r a s s es g e r m i n a t e, t he root e m e r g es f i r st and then the m e s o c o t yl b e g i ns to e l o n- g a t e, pushing the c o l e o p t i le up t h r o u gh the s o i l. E l o n g a t i on of the m e s o c o t yl c e a s es w h en light s t r i k es the c o l e o p t i le ( F i g. 5). T he s t em a b o ve the a t t a c h m e nt b e g i ns to e l o n g a t e, the p l u m u le c o n t i n u es expanding, the c o l e o p t i le s p l i ts and the shoot e m e r g e s. S e c o n d a ry r o o ts e m e r ge t he node w h e re the c o l e o p t i le w as a t t a c h e d. f r om F i g u re 5. C e ll d i v i s i on is u s u a l ly d i v i d ed into two p a r t s. T he d i v i s i on is c a l l ed m i t o s i s, of the n u c l e us and i ts a s s o c i a t ed c h r o m o s o m es and the s u b s e q u e nt d i v i s i on of the c y t o p l a sm into two p a r ts and the f o r m a t i on of a c e ll w a ll b e t w e en the two n u c l ei is c a l l ed c y t o- k i n e s i s. It is w e ll r e c o g n i z ed that the c a r b a m a t e s, s u ch as p r o p h a m, c h l o r o p r o p h a m, E P TC and v e r n o l a t e, a re i n h i b i t o rs of c e ll d i v i- sion. F u r t h e r m o r e, t h e ir p r i m a ry e f f e ct s e e ms to be on c y t o- k i n e s i s, r a t h er than on m i t o s i s. T he n u m e r o us s i m i l a r i t i es b e- t w e en t h e ir e f f e c ts and the e f f e c ts of b e n e f i n, b e n s u l i d e, D C PA and t e r b u t ol s u g g e st that inhibition of c e ll d i v i s i on m ay a l so be the p r i m a ry m o de of a c t i on of the l a t t er g r o u p. M a ny p e o p le h a ve w o r k ed with h e r b i c i d es c a u s i ng inhibition of c e ll d i v i s i on ( D o x e y, 1949; E n n i s, 1949; I v e ns and B l a c k m a n, 1950; M a n n, J o r d an and D a y, 1965; Mann and S t o r e y, 1966; S a w a m u r a, 1965). A r e v i ew of t h e se p a p e rs e s t a b l i s h es the f o l- l o w i ng as r a t h er c o m m on e f f e c ts of t h e se h e r b i c i d e s: 1. T h ey b e h a ve s o m e w h at l i ke the c h e m i c al c o l c h o c i ne in that t h ey m ay c a u se a doubling of c h r o m o s o me n u m b e r s. A f- f e c t ed c e l ls i n c r e a se in s i ze and do not continue spindle d e v e l- o p m e n t. P o l y p l o i dy and m u l t i n u c l e a te c e l ls a re c o m m o n. 2. R o ot t i ps stop e l o n g a t i n g, s w e ll and b e c o me k n o b by in a p p e a r a n c e. N u m e r o us l a t e r al r o o ts initiate and then u n d e r go t h e se s a me c h a n g e s. T he r o ot tip s w e l l i ng r e s u l ts p r i m a r i ly f r om r a d i al g r o w th in the p e r i c y c le and e n d o d e r m i s. 3. G r a s s e s, and m o n o c o ts in g e n e r a l, a re m o re s e n s i t i ve t h an d i c o t s. One of t h e se o b s e r v a t i o ns s e e ms to w a r r a nt a d d i- t i o n al c o m m e n t; that the g r a s s es and o t h er m o n o c o ts a re m o re s e n s i t i ve than the d i c o t s. T h is is p r o b a b ly e x p l a i n a b le in t e r ms of n u m b e rs and p o s i t i o ns of the m e r i s t e m s. In d i c o ts that g e r- m i n a te l i ke cotton and k i d n ey b e a n s, the only m e r i s t em e x p o s ed to the c h e m i c a l ly t r e a t ed s o il is the root tip, and then only if g e r m i n a t i on o c c u rs in the t r e a t ed l a y e r. If the r o ot m a n a g es to e n t er u n t r e a t ed s o i l, the plant w i ll s u r v i v e. T he p l u m u le is p r o- t e c t ed as it p e n e t r a t es the t r e a t ed s o i l. C e ll d i v i s i on i n h i b i t o rs a re u s u a l ly a p p l i ed as p r e - e m e r g e n ce h e r b i c i d es to the s u r f a ce of the s o i l, or i n c o r p o r a t ed in the u p p er s u r f a c e. It is not un- c o m m on to s ee a d i c ot s e e d l i ng e m e r ge and then die b e c a u se t h e re is not a s u f f i c i e nt root s y s t em to m a i n t a in the g r o w th of the plant. H o w e v e r, g r a ss not only h as the r o ot tip in the t r e a t ed s o il but a l so the p l u m u le and m e r i s t e ms a b o ve and b e l ow the a t t a c h- m e nt of the c o l e o p t i le a re r e l a t i v e ly e x p o s e d. T he bulk of the r o ot s y s t e m, the a d v e n t i t i o us r o o t s, o r i g i- It is a l w a ys n e ar the s u r f a ce n a te f r om t h is s a me node ( F i g. 4). and, t h u s, in the c h e m i c al t r e a t ed s o il b e c a u se the e p i c o t yl e l o n g a t es until light s t r i k es the c o l e o p t i l e. R e c e nt w o rk h as e s t a b l i s h ed the i m p o r t a n ce of the p o s i t i on of the c h e m i c a l ly t r e a t ed s o il with r e f e r e n ce to t h e se m e r i s t e ms e f f i c i e n cy of t h e se h e r b i c i d e s. in a f f e c t i ng the R e s e a r c h e rs a re c u r r e n t ly a t t e m p t i ng to e x p l a in a ll h e r b i- c i d al a c t i on in t e r ms of t h e ir e f f e c ts on p r o t e in s y n t h e s i s. is o b v i o us that d i v i d i ng c e l ls m u st be m a k i ng D NA and R NA and so it is not s u r p r i s i ng to find that h e r b i c i d es inhibiting c e ll d i v- i s i on a f f e ct p r o t e in s y n t h e s i s. i n- t e r f e r e n ce with p r o t e in s y n t h e s is as the m o de of a c t i on of t h e se h e r b i c i d es s i n ce t h is e f f e ct p r e c e d es the e f f e ct on c e ll d i v i s i o n. H o w e v e r, t h e re a re m a ny h e r b i c i d es that a f f e ct p r o t e in s y n t h e s is that do not s t r o n g ly inhibit c e ll d i v i s i o n. It m i g ht be p r e f e r a b le to l i st It D. J. W o rt in a book edited by A u d us (1964) h as s u m m a r- i z ed the e f f e c ts of h e r b i c i d es on p r o t e in s y n t h e s i s. Mann, J o r- d an and D ay (1965) and, l a t e r, M o r e l a nd et al. (1969) u s ed r a d i o- l a b e l ed a m i no a c i ds to s c r e en h e r b i c i d es f or t h e ir e f f e c ts on a m i no a c id a b s o r p t i on and i n c o r p o r a t i on into p r o t e i n. h e r b i c i d es w e re shown to i n f l u e n ce t h e se p r o c e s s e s, but the f u ll s i g n i f i c a n ce of t h e se f i n d i n gs in r e l a t i on to t h e ir h e r b i c i d al a c- t i v i ty is not k n o w. S e v e r al D i s t u r b a n ce of H o r m o n al G r o w th R e g u l a t i on T h o se h e r b i c i d es that e f f e ct h o r m o n al g r o w th r e g u l a t i on a ll h a ve the a b i l i ty to m o d i fy n o r m al g r o w th p a t t e r n s. S o me a r e as of c e ll d i v i s i on m ay stop f u n c t i o n i ng and n ew a r e as a re o f t en i n i t i a t e d. T he r e s u lt is a h i g h ly d i s t o r t ed plant. T h e se a l t e r- a t i o ns in c e ll d i v i s i on c l e a r ly s u g g e st a l t e r a t i o ns in p r o t e in s y n t h e s i s, w h i ch h as b e en c o n f i r m e d. T he m o de of a c t i on of the g r o w th r e g u l a t i ng h e r b i c i d e s, s u ch as 2 , 4 - D, 2 , 4 , 5 -T and M C P A, h as b e en m o re t h o r o u g h ly i n v e s t i g a t ed than any o t h er g r o up of h e r b i c i d e s. But t h e ir p r e c i se m o de or m o d es of a c- t i on r e m a i ns unknown. F r om a p r a c t i c al standpoint, the f o l l o w i ng a re i m p o r t a nt f a c ts f or a ll of the h e r b i c i d es that I h a ve p l a c ed in this c a t e- g o r y, with the e x c e p t i on of dalapon: 1. The h e r b i c i d e s, in g e n e r a l, a re m o re e f f e c t i ve a g a i n st b r o a d l e a v ed w e e ds than a g a i n st g r a s s e s. 2. T h ey a re u s u a l ly a p p l i ed as f o l i ar s p r a y s. 3. T h ey a re e f f e c t i ve at v e ry l ow r a t es of a p p l i c a t i o n. 4. T h ey m ay be t r a n s l o c a t ed f r om the l e a v es to the r o o ts and c a u se d e a th of u n d e r g r o u nd o r g a n s. 5. B e c a u se t h ey a re t r a n s l o c a t ed d o w n w a r d, t h ey a re e f- f e c t i ve a g a i n st s o me p e r e n n i a l s. 6. B e c a u se t h ey a re e f f e c t i ve in v e ry l ow d o s es and b e c a u se m a ny p r i z ed o r n a m e n t a ls a re quite s e n s i t i v e, d r i ft of t h e se h e r- b i c i d es c an c a u se s e r i o us p r o b l e m s. 7. T he d e g r ee of g r o w th d i s t o r t i on is not an i n d ex of the e a se of k i l l i ng the plant. M a ny p l a n t s, s u ch as cotton, c an h a ve quite n o t i c e a b le d i s t o r t i on without being k i l l ed or s e r i o u s ly r e- d u c i ng the y i e l d. It is p e r h a ps a m i s t a ke to i n c l u de d a l a p on in the s a me g r o up w i th d i c a m b a, s i l v e x, 2 , 4 -D and 2 , 4 , 5 - T. a g a i n st g r a s s es than a g a i n st b r o a d l e af p l a n ts and r e q u i r es high a p p l i c a t i on r a t es to induce k i l l. W o rk done with m i c r o o r g a n i s ms by Hilton et al. (1959) i n d i c a t es that one m a j or s i te of i ts a c t i on m ay be i n h i b i t i on of pantothenate s y n t h e s i s; h o w e v e r, t h e re It is m o re e f f e c t i ve is s o me doubt about t h is as the p r i m a ry m o de of a c t i on in h i g h er p l a n t s. In o t h er r e s p e c t s, d a l a p on is s i m i l ar to o t h er g r o w th r e g u l a t i ng h e r b i c i d e s. F r ee R a d i c a ls E f f e c ts on S u l f h y d r yl E n z y m es T he f i n al g r o up of c h e m i c a ls a re the b i p y r i d i n um s a l t s, w h i ch i n c l u de p a r a q u a t. P a r a q u at could h a ve b e en i n c l u d ed in the l i st of p h o t o s y n t h e s is i n h i b i t o rs but it is a p p a r e n t, f r om its v e ry r a p id k i l l i ng p o w e r, that t h is is not its p r i m a ry m o de of a c t i o n. T he c u r r e nt s t a t us of our k n o w l e d ge of the a c t i on of the b i p y r i d i n i u ms is w e ll c o v e r ed in a p a p er by Z w e ig et al. (1969). W h en a p p l i ed as a f o l i ar s p r a y, p a r a q u at q u i c k ly k i l ls a ll g r e en p a r ts of the plant it c o n t a c ts that a re e x p o s ed to light. E l e c t r o ns m a de a v a i l a b le d u r i ng p h o t o s y n t h e s i s, as d e s c r i b ed e a r l i e r, a re u s ed to c o n v e rt the b i p y r i d i n i um s a lt to i ts f r ee r a d i c al f o r m. T h is f r ee r a d i c a l, in t u r n, c a u s es the f o r m a t i on of o t h er f r ee r a d i c a l s. T he h e r b i c i de t h e r e by b e c o m es r e o x i- d i z ed and is a g a in r e a dy to c a p t u re a n o t h er e l e c t r on and r e p e at the p r o c e ss a ll o v er a g a i n. S i n ce o x y g en is a l so n e c e s s a ry f or the c o m p o u nd to be t o x i c, it is a s s u m ed that H 2 O 20 a n c* O H° a re a m o ng the f r ee r a d i c a ls p r o d u c e d. If this is t r u e, the t o x ic a c- t i on of p a r a q u at is quite s i m i l ar to that of i o n i z i ng r a d i a t i on and one of its p r i m a ry r e a c t i o ns would be the i n a c t i v a t i on of s u l f- h y d r yl e n z y m es as d i a g r a m m ed b e l o w. T he f o l l o w i ng a re i m p o r t a nt c o n s i d e r a t i o ns in f i e ld a p p l i- c a t i o ns of p a r a q u a t: 1. T he compound is v e ry t e n a c i o u s ly a d s o r b ed and is i n- a c t i v a t ed q u i c k ly in s o i ls containing c l a y. 2. T he h e r b i c i de k i l ls only the plant p a r ts it c o n t a c t s. It h as e s s e n t i a l ly no r e s i d u al a c t i v i ty and is not a p p r e c i a b ly l o c a t e d. t r a n s- 3. It is m u ch m o re e f f e c t i ve in the light than in the d a rk and a g a i n st g r e en than n o n - g r e en t i s s u e s. 4. T he slight t o x i c i ty in the d a rk and a g a i n st n o n - g r e en t i s s ue is thought to be due to f r ee r a d i c al f o r m a t i on c u a s ed by r e d u c t i on m e c h a n i s ms a s s o c i a t ed with r e s p i r a t i on (Andus, 1964). 5. Of the c o m m o n ly u s ed h e r b i c i d e s, p a r a q u at is one of the m o st t o x ic to m a n. S u m m a ry I h a ve t r i ed to c o v er s o me of the m o re s i g n i f i c a nt a s p e c ts of the p r i m a ry m o d es of a c t i on of c o m m on h e r b i c i d e s. H e r b i- c i d es w e re s o m e t i m e s, f or c o n v e n i e n c e, p l a c ed into c a t e g o r i es without s u f f i c i e nt i n f o r m a t i on about t h e ir p r i m a ry m o de of a c- tion. An a t t e m pt h as b e en m a de h e re to show how a k n o w l e d ge of the m o de of a c t i on c an be u s ed to e x p l a in how h e r b i c i d es a ct in the f i e l d. A c k n o w l e d g e m e n t. We w i sh to g i ve c r e d it to the t e xt " B o t- a n y ", by W i l s on and L o o m i s, Holt, R i n e h a r t, and W i n s t o n, f or F i g u r es 1, 2, 3, 4 and 5. R e f e r e n c es C i t ed A r n o n, D. I. I960. T he r o le of light in p h o t o s y n t h e s i s. S c i- e n t i f ic A m e r i c an 203 (5): 1 0 5 - 1 1 8. A s h t o n, F. M. 1965. P h y s i o l o g i c a l, b i o c h e m i c a l, and s t r u c- t u r al m o d i f i c a t i o ns of p l a n ts induced by a t r a z i ne and m o n- u r o n. P r o c. S o u t h e rn W e ed Conf. 18:596-602. A n d u s, L. J. (ed.). 1964. T he p h y s i o l o gy and b i o c h e m i s t ry of h e r b i c i d e s. A c a d e m ic P r e s s, Inc., N ew Y o r k. 555 pp. C o o k e, A. R. 1956. A p o s s i b le m e c h a n i sm of a c t i on of the u r ea t y pe h e r b i c i d e s. W e e ds 4 : 3 9 7 - 3 9 8. D o x e y, D. 1949. T he e f f e ct of i s o p r o p yl c a r b a m a te on m i t o s is in r ye ( S e c a le c e r e a l e) and onion ( A l l i um cepa) Ann. B o t. 1 3 : 3 2 9 - 3 3 5. E n n i s, W. B ., J r. 1949. H i s t o l o g i c al and c y t o l o g i c al r e s p o n se of c e r t a in p l a n ts to s o me a r yl c a r b a m ic e s t e r s. A m. J o u r. B o t. 36:823. F o g g, G. E. 1968. P h o t o s y n t h e s i s. A m e r i c an E l s e v i er P u b- l i s h i ng C o ., Inc. N ew Y o r k. 1 16 pp. G o o d, N. E. 1 9 6 1. I n h i b i t o rs of the H i ll r e a c t i o n. P l a nt P h y i o l. 36:788-803. G o o d, N. E. 1962. I n h i b i t o rs of p h o t o s y n t h e s is as h e r b i c i d e s. W o r ld R e v. P e st C o n t r o l, pp. 1 9 - 2 8. H i l t o n, J. L ., J. S. A r d, L. L. J a n s en and W. A. G e n t n e r. 1959. T he p a n t o t h e n a t e - s y n t h e s i z i ng e m z y m e, a m e t a b o l ic s i te in h e r b i c i d al a c t i on of c h l o r i n a t ed a l i p h a t ic a c i d s. W e e ds 7: 3 8 1 - 3 9 6. I v e n s, G. W. and G. E. B l a c k m a n. Inhibition of g r o w th of a p i c al m e r i s t e ms by e t h yl p h e n yl c a r b a m a t e. N a t u re 1 6 6 : 9 5 4 - 9 5 5. 1950. L e v i n e, R. P. T he m e c h a n i s ms of p h o t o s y n t h e s i s. S c i e n t i f ic A m e r i c an 221 (6):58-70. L o t l i k a r, P. D ., L. F. R e m m e rt and V. H. F r e e d. 1968. E f- f e c ts of 2 , 4 -D and o t h er h e r b i c i d es on o x i d a t i ve p h o s p h o r y- l a t i on in m i t o c h o n d r ia f r om c a b b a g e. W e ed S c i. 1 6 : 1 6 1 - 1 6 5. M a n n, J. D ., L. S. J o r d an and B. E. D a y. 1965a. T he e f f e c ts of c a r b a m a te h e r b i c i d es on p o l y m er s y n t h e s i s. W e e ds 1 3 : 6 3- 66. M a n n, J. D ., L. S. J o r d an and B. E. D a y. 1965b. A s u r v ey of h e r b i c i d es f or t h e ir e f f e c ts upon p r o t e in s y n t h e s i s. P l a nt P h y s i o l. 40:840-843. M a n n, J ay D. and W i l l i am B. S t o r e y. 1966. R a p id a c t i on of c a r- b a m a te h e r b i c i d es upon plant c e ll n u c l e i. C y t o l o g ia 31:203- 207. M o r e l a n d, D. E ., S. S. M a l h o t r a, R. D. G r u e n h a g en and E. H. S o k r a i i. s y n t h e s i s. W e ed S c i. 1 7 : 5 5 6 - 5 6 3. 1969. E f f e c ts of h e r b i c i d es on R NA and p r o t e in v an O v e r b e e k, J. 1962. P h y s i o l o g i c al r e s p o n se of p l a n ts to h e r b i c i d e s. W e e ds 1 0 : 1 7 0 - 1 7 4. R e i d, J. 1 9 5 7. C o m p a r i s on of s a l i c y l a te and 2 : 4 - d i n i t ro phenol on the g r o w th of w h e at c o l e o p t i l e s. N a t u re 1 7 9 - 4 8 4. S a w a m u r a, S. 1965. C y t o l o g i c al s t u d i es on the e f f e c ts of h e r- b i c i d es on plant c e l ls in v i v o. 2. N o n - h o r m o n ic h e r b i- c i d e s. C y t o l o g ia 30:32 5 - 3 4 8. S w e e t z e r, P. B. and C. W. T o d d. 1 9 6 1. T he e f f e ct of m o n u r on on o x y g en l i b e r a t i on in p h o t o s y n t h e s i s. B i o c h e m. et B i o p h y s. A c ta 51:504-508. W e i n b a c h, E. C. 1956. B i o c h e m i c al b a s is f or the t o x i c i ty of p e n t a c h l o r o p h e n o l. S c i e n ce 124:93 5. W e s s e l s, J. S. C. and R. v an d er V e e n. a c t i on of s o me d e r i v a t i v es of p h e n y l - u r e t h an and of 3 - p h e n y l - 1 , 1- d i m e t h y l u r ea on the H i ll r e a c t i o n. B i o c h e m. et B i o p h y s. A c ta 1 9 : 5 4 8 - 5 4 9. 1956. T he Z w e i g, G u n t e r, J. E. Hitt and D. H. C h o. 1969. M o de of a c t i on J. A g r. F o od of d i p y r i d y ls and c e r t a in quinone h e r b i c i d e s. C h e m. 1 7 : 1 7 6 - 1 8 1. D i s c u s s i on P e r i od D r. D a n i e l: Do you h a ve any o b s e r v a t i o ns on p o t a s s i um a z i d e? I tfs b e en t e s t ed a l i t t le on s o me t h i n g s. D r. D i c k e n s: W e ' ve done s o me t e s t i ng on f o r a ge c r o p s, but not on t u r f. D r. H a r ry A m l i ng h as done s o me w o rk with h o r t i c u l- t u re c r o ps and it a p p e a rs to do a p r e t ty good j o b - - s o m e t h i ng s i m i l ar to c a l c i um c y a n i d e. I ' ve s t a y ed a w ay f r om it b e c a u se of the t o x i c i t y. o w n er u s e. I don't think it w i ll e v er be a p p r o v ed f or h o m e- D r. H e m p h i l l: We h a ve u s ed t h is in h o p es of getting rid of of the c o t t o n f i e l d - t y pe b e r m u d a, but u n f o r t u n a t e ly i t 's j u st a k n o c k d o wn and it c o m es b a ck v e ry s h o r t l y. s o me D r. D i c k e n s: W as t h is i n c o r p o r a t ed in the s o i l? D r. H e m p h i l l: No, t h is w as a s u r f a ce f o l i ar a p p l i c a t i o n. D r. D i c k e n s: O u rs w as i n c o r p o r a t ed and k e pt w a t e r ed in. I'd q u e s t i on w h e t h er or not the r a p id b u rn e f f e ct D r. S w i t z e r: f r om D N B P, p a r a q u at or any of t h e se o t h e rs is d i r e c t ly r e l a t ed to its e f f e ct on the r e s p i r a t i on s y s t e m. D r. D i c k e n s: I'd q u e s t i on that m y s e l f. I'd r a t h er think t h is is a m a t t er of p e r m e a b i l i ty D r. S w i t z e r: e f f e c t. h a ve an e f f e ct on m i t o c h o n d r i al r e s p i r a t i o n, but I don't think the q u i ck b u rn is a r e s u l t - of r e s p i r a t i o n. If y ou put it on at a l ow enough r a te you a re going to D r. D i c k e n s: I t 's too f a s t, I f e e l, to be the c a u s e. I would l i ke to c o m m e nt about d i n o s eb on the D r. B i n g h a m: m i t o c h o n d r i a. T he e f f e ct s e e ms to t a ke p l a ce on the m e m b r a ne w h e re the e l e c t r on n o r m a l ly t r a v e ls t h r o u gh the c y t o c h r o me s y s t em in the m e m b r a n e. D i n o s eb t e a rs up the m e m b r a ne and a l l o ws t h e se e l e c t r o ns to f r e e w h e el t h r o u gh the m e m b r a n e. O n ly a v e ry s m a ll a m o u nt of A TP is f o r m ed o n ce you get t h is f r e e w h e e l i n g. O r d i n a r i l y, about t h r ee A T P 's a re f o r m ed f or e a ch o x y g en s u p p l i ed with an e l e c t r o n. V e ry l i t t le A TP ed if the m e m b r a ne is t o r n. if f o r m- I think an i n t e r e s t i ng o b s e r v a t i on on d i n o s e b, or D r. A h r e n s: D N B P, w h en it is t a k en up t h r o u gh r o o t s, is that it o b v i o u s ly d o es d e s t r oy m e m b r a n e s. It c an m o ve with t r a n s p i r a t i on w a t e r, p a ss out of l e a v es i n t a c t, and i n j u re o t h er l e a v es that it t o u c h e s. is the f i r st h e r b i c i de that I h a ve e v er s e en do that. It I 'm one of t h o se who d o e s n 't f e el it is v e ry h a z- I'd l i ke to h e ar s o me d i s c u s s i on f r om o t h e rs on the r e l a t i ve h a z- a rd of p a r a q u a t. a r d o us w h en u s ed p r o p e r l y. W e ' ve had a lot of p e o p le s c a r ed a w ay f r om it, I f e e l, to o t h er t h i n gs that m i g ht be m o re t o x i c, l i ke d i n o s e b. we h a v e. Its s u ch a u s e f ul tool; the b e st c h e m i c al hoe that I'd l i ke to h e ar s o me o t h er c o m m e n ts on it. D r. D i c k e n s: p r o p e r ly u s e d ." T h a t 's the thing I w o r ry about. I think y ou hit it on the h e ad w h en you s a i d, " w h en I m i g ht c o m m e nt on p a r a q u a t, s i n ce I am p r o b a b ly D r. D e w e y: r e s p o n s i b le f or a lot of the c o n c e rn and p u b l i c i ty that it w as g i v e n. We had o b s e r v ed t h is m a t e r i al being u s ed on a r a t h er l a r ge s c a l e, and in m a ny i n s t a n c es with no p r e c a u t i o ns being t a k en w h a t s o e v e r. T h is w as p a r t i c u l a r ly t r ue with the d e f o l i a- t i on of p o t a to v i n e s, w h e re the m a t e r i a ls w e re a p p l i ed by a ir and the f l a g m en in the f i e l ds w e re standing in the d r i f t. We a l so h ad p e o p le that w e re r a t h er r e c k l e s s - - u s i ng k n a p s a ck s p r a y e rs in o r c h a rd s i t u a t i o n s. C o n s e q u e n t l y, in going t h r o u gh the l i t e r- a t u r e, we found that t h e re w e re m a ny a c c i d e n t al d e a t hs r e s u l t- ing f r om the i n h a l a t i on of d r o p l e ts or a c c i d e n t a l ly s w a l l o w i ng the m a t e r i a l. S i n ce the a c t i on w as i r r e v e r s i b l e, with no a n t i- d o t e, and the length of t i me it took f or a n y w h e re f r om 16 h o u rs to 21 d a y s, it s e e m ed that the l e a st we c o u ld do w as to c a ll attention to the p r o b l em and to t a ke p r o p er It w as t h is o b j e c t i ve that we had in p r e c a u t i o n a ry m e a s u r e s. It got a l i t- m i nd w h en we s t a r t ed g i v i ng t h is m a t t er p u b l i c i t y. t le bit out of hand as it w as p a s s ed f r om one p e r s on to a n o t h e r, as u s u a l ly h a p p e n s. But s h o r t ly a f t er that, p a r a q u at c o n t a i n e rs c a me out with a p o i s on l a b e l. A ll we w e re r e a l ly a s k i ng w as that p e o p le a d h e re to the r u l es and the w a r n i ng that w e re a l r e a dy on the c o n t a i n e r, but w e re not being o b s e r v e d. A c t u a l l y, we w e re f a t a l i t i es to o c c ur v a r i ed d o i ng this b e c a u se we f e lt this m a t e r i al had a g r e at f u t u r e. We w a n t ed to m a ke c e r t a in that we did not e n c o u n t er a s e r i es of a c- c i d e n ts that would c a u se the l o ss of i ts u s e. t e nt to t ry to run p a r a q u at out of b u s i n e ss on a s c a re p h i l o s o p h y. It w as not our i n- M r. S e e l y: When I w as in A u s t r a l ia a y e ar and a half a g o, the p e o p le w e re v e ry m u ch i n t e r e s t ed in the f a ct that we w e re not u s i ng p a r a q u a t. T h ey w e re u s i ng it on w i de s c a le b a s is with no p r o b l e ms w h a t s o e v e r. As a c o n s e q u e n c e, t h ey w e re w o n d e r i ng w hy we w e re a ll c o n c e r n ed about it. A c t u a l l y, I would a g r ee that we n e ed to u se c a u t i on with m a t e r i a ls w h i ch a re h i g h ly t o x i c, it s u ch as d i n o s e b, w h i ch h as an L-D50 of only 40. We a re u s i ng in v e ry l a r ge q u a n t i t i es and i t 's i n c r e a s i ng r a p i d l y, s i n ce this is a v e ry r a p i d ly d i s s i p a t ed m a t e r i a l. We don't a n t i c i p a te any p r o- b l e ms the m o re p e r s i s t e nt c o m p o u n d s. in r e g i s t e r i ng t h e se m a t e r i a l s, as c o m p a r ed to s o me of I k n ow that t h i n gs l i ke d i n o s e b, D r. T i m m o n s: d a z o l es f r om F i s o n, i o x y n il and o t h er p h e n o ls a re a ll o x i d a t i ve p h o s p h o r y l a t i on i n h i b i t o rs or u n c o u p l e r s. c o n t r ol a m o ng g r a s sy s p e c i e s. I am c u r i o us if t h e se o t h er m a- t e r i a ls a re a l so p r i m a r i ly b r o a d l e af c o n t r o ls in g r a s s es and if t h ey a r e, w hy a re t h e y? I o x y n il is a b r o a d l e af t r i f l u o r o b e n z i m i- (No r e s p o n s e) D r. N e w m a n: W h i le p a r a q u at is a b s o r b ed onto c l a ys v e ry r a p- i d ly and is i n a c t i v a t e d, is t h e re any r e al e v i d e n ce to show j u st e x a c t ly w h at h a p p e ns to that m o l e c u le a f t er it is a b s o r b e d? Is it d e g r a d e d, or i s n 't it? What is the f a te of t h is thing as a r e- s u lt of c o n t i n u o us u s e? I think t h is is a q u e s t i on in s o me p e o- p l e 's m i n d s. I c a n 't a n s w er t h is d i r e c t l y, but I c an g i ve you s o me a p- M r. S e e l y: i n d i r e ct i n f o r m a t i on on it. We h a ve b e en m a k i ng c o n t i n u al p l i c a t i o ns of the m a t e r i al f or a n u m b er of y e a rs in the s a me g e n e r al a r e a s. A l t h o u gh we h a ve no d i r e ct s t u d i es i n d i c a t i ng that the m a t e r i al h as b e c o me a c t i v e, plant g r o w th on the t r e a t ed a r e as h as b e en on the d o w n g r a de now f or the l a st t h r ee or f o ur y e a r s, as c o n t r a s t ed to t h o se w h i ch a re not getting the m a t e r i a l. T h is w o u ld i m p ly that s o me of the m a t e r i al is b e c o m i ng a v a i l- a b l e. W e ' re s t i ll getting a v e ry r a p id t ie up of an i m m e d i a te a p- p l i c a t i on in the s o i l, but a p p a r e n t ly s o me of the m a t e r i al is b e- c o m i ng a v a i l a b l e. l o i d. I think it is b e i ng s l o w ly r e l e a s ed off the c o l- D r. B u r t: We h a ve u s ed it f or e d g i n g, a r o u nd f l o w er b e ds and t h i n gs l i ke that on o ur sandy s o i l s, and h a ve had r e s i d u al f or as m u ch as 12 m o n t h s - - r e t a r d i n g, p e g g i ng down of t u r f g r a s s e s. O ur r e s u l ts a re s i m i l ar to t h o se of M r. S e e l y. I am a w a re of the f a ct that the e f f i c i e n cy of p a r a- M r. S c h e e r: quat c an be i n c r e a s ed t h r o u gh addition of c e r t a in s u r f a c t a n ts at c e r t a in c o n c e n t r a t i o n s. D o es anyone h e re h a ve any e x p e r i e n ce on t h is s u b j e c t? D r. D i c k e n s: T h e re h as b e en s o me w o rk done on v a r i o us c o n- c e n t r a t i o n s, but I c a n 't t e ll you w h at the e f f e c ts w e r e - - b o th in the a m o u nt of dilutant and the p e r c e n t a ge c o n c e n t r a t i o n. t h e y ' ve both b e en w o r k ed on. w as on that. I don't r e c a ll what the s i t u a t i on In f a c t, I ' ve a l w a ys had the i m p r e s s i on that p a r a q u at w as D r. H e m p h i l l: I u s ed it on a d e g r a d ed or i n a c t i v a t ed v e ry q u i c k ly in the s o i l. g r a v el d r i v e w ay to k i ll s o me b l u e g r a ss and w e e d s, and it k i l l ed the b l u e g r a ss t u rf f or about one foot into the t u rf a r e a. T h is w as put on w i th a w a t e r i ng can; it w a s n 't s p r ay d r i f t. E v i d e n t l y, it d o es s t ay a r o u nd f or quite a w h i le and w i ll m o ve in the s o i l. I think D r. J. B. W e b er at N o r th C a r o l i na State U n i- P a r- D r. G r e e n: v e r s i ty h as done quite a lot of w o rk on a d s o r p t i on on s o i l s. a q u at and diquat, b e c a u se t h ey a re c a t i o n s, a re a d s o r b ed p r e t ty m u ch l i ke c a l c i u m, s o d i um and h y d r o g e n, e x c e pt that t h e ir a f- f i n i ty is m u ch g r e a t er than t h e se i o n s. T h e re is a d i f f e r e nt s e- l e c t i v i ty of t h e se c o m p o u n ds f or d i f f e r e nt c l a y s - - m o n t m o r i l l o n- i t e, f or e x a m p l e. M o st l o w - l a nd s o i ls containing m o n t m o r i l l o n- i te w i ll tend to a d s o rb p a r a q u at and diquat to a g r e at extent. K a o l i n i t e, the m o re w e a t h e r ed c l a y s, and sand with t h e ir l ow e x c h a n ge c a p a c i ty w i ll tend to a d s o rb the c o m p o u n ds l e s s. O v er a p e r i od of t i me t h e se e x c h a n g e a b le c a t i o ns c an be r e l e a s ed b a ck into the s o il s o l u t i on t h r o u gh e x c h a n ge with m e t a l l ic c a t- i o n s. D r. D i c k e n s: If I!m not m i s t a k e n, O r t ho or C h e v r on had quite a p r o b l em in r e c o v e r i ng t h e se c a t i o n s. In o t h er w o r d s, t h ey put a g i v en a m o u nt on, it didn't c o me out of the b o t t om of the c o l u mn and t h ey c o u l d n 't find it in the c o l u mn on s o me of the c l ay m i n e r a l s. T h ey f i n a l ly found it w i th an x - r ay s p e c t r o- g r a ph in b e t w e en the l a t i ce of the i n d i v i d u al c l ay m o l e c u l e s. Of c o u r s e, y o ur expanding t y pe or m o n t m o r i l l o n i te c l a ys w o u ld t r ap m o re in t h is r e s p e c t, too. it is not a v a i l a b le f or o r g a n i s m s. A l s o, the w o rk f or D r. K a u f m a n: T h is is a v e ry b i o d e g r a d a b le c o m p o u nd and, f r om my own v i e w p o i n t, I c o n s i d er it to be one of the m o re r e a d i ly d e g r a d a b le c o m p o u n d s. B e c a u se it is v e ry t i g h t ly a d s o r b e d, J e r ry W e b b er had done i n d i c a t es that it is not a v a i l a b le d e g r a d a t i o n. T he m o m e nt it b e c o m es a v a i l a b l e, it d o es s e em to be r e a d i ly d e g r a d ed now. is doing at B e l t s v i l l e, w h i ch is not p u b l i s h ed y e t, t h e re a re i n d i c a t i o ns that with continued u se of t h i s, t h e re m ay be a s a t u r a t i on of the s o i l. O n ce you get to a c e r t a in l e v e l, i t 's no l o n g er a d s o r b ed and it w i ll l e a c h, as w e ll as b e c o me a v a i l- a b le f or t o x ic p u r p o s e s. In s o me o t h er w o rk D r. H e e l i ng U N I Q UE A P P R O A C H ES TO W E ED C O N T R OL W i l l i am E. S t o t t l e m y er and R i c h a rd B a i l ey B i o - C h e m i c al R e s e a r ch O. M. S c o tt & Sons C o m p a ny M a r y s v i l l e, Ohio 43040 I n t r o d u c t i on A l t h o u gh the t i t le of t h is p a p er is " U n i q ue A p p r o a c h es to W e ed C o n t r o l ," I w o u ld l i ke to point out that the a p p r o a c h es to be d i s c u s s ed a re not o r i g i n al with o ur r e s e a r ch g r o u p. I n f o r- m a t i on p r e s e n t ed is l a r g e ly t a k en f r om the l i t e r a t u r e. H o w- e v e r, t h ey a re unique in the s e n se that f ew i n v e s t i g a t o rs a re u s i ng t h e m. T h r ee a p p r o a c h es w i ll be d i s c u s s e d. F i r s t, if we could m a ke d e s i r a b le p l a n t s, in o ur c a se t u r f g r a s s e s, m o re c o m p e t i- t i v e, the d e s i r a b le p l a n ts with a b e t t er c o m p e t i t i ve a d v a n t a ge w o u ld c r o wd out the u n d e s i r a b le p l a n t s, the w e e d s. Or a l t e r- n a t i v e l y, if we could m a ke the w e e ds l e ss c o m p e t i t i v e, then o n ce a g a in the d e s i r a b le p l a n ts would c r o wd out the u n d e s i r- a b le p l a n t s. W h en we f o l l ow good c u l t u r al p r a c t i c e s, such as p r o p er m o w i n g, f e r t i l i z a t i on and i r r i g a t i o n, we e n c o u r a ge d e n s e, v i g o r o us t u r f; h o w e v e r, o t h er f o r c es a re at w o rk to c o u n t e r a ct p a rt of t h is e f f o r t. T u rf d i s e a s e s, i n s e c t s, n e m a t o d es and t r a f- f ic r e p r e s e nt s o me of t h e se f o r c e s. With m o re c o m p e t i t i ve t u r f g r a s s e s, the e f f e c ts of m a ny of t h e se n e g a t i ve f a c t o rs could be g r e a t ly r e d u c e d. In the l a st f ew y e a rs a l a r ge a m o u nt of r e- s e a r ch h as b e en done on C 0 2 - a s s i m i l a t i on in p l a n t s. B l a ck et a l. (1969) h a ve s u g g e s t ed that e f f i c i e nt C 0 2 - a s s i m i l a t i ng p l a n ts a re m u ch m o re c o m p e t i t i ve than n o n - e f f i c i e nt C O 2 - a s s i m i l a t- ing. An e x a m p le of an e f f i c i e nt C 0 2 - u t i l i z i ng plant is c r a b- g r a ss and an e x a m p le of a n o n - e f f i c i e nt of C 0 2 - u t i l i z i ng plant K e n t u c ky b l u e g r a s s. is T he s e c o nd t o p ic to be d i s c u s s ed is c h e m i c a l - g e n o t y pe i n- t e r a c t i o n s. We a re a ll a w a re of i n s t a n c es w h e re d i s e a se o r g a n- i s ms h a ve d e v e l o p ed r e s i s t a n ce to a n t i b i o t i c s, w h e re h o u s e f l i es h a ve d e v e l o p ed r e s i s t a n ce to D DT and w h e re c e r t a in w e e ds h a ve d e v e l o p ed r e s i s t a n ce to h e r b i c i d e s. We w o u ld l i ke to t u rn this thing a r o u n d. T h at i s, d e v e l op t u r f g r a ss v a r i e t i es w h i ch a re r e s i s t a nt to a s p e c i f ic h e r b i c i d e. T h en the r e s i s t a nt v a r i e t i es c o u ld be t r e a t ed w i th the h e r b i c i de and the w e e ds in t u rf would be k i l l ed without d a m a g i ng the t u r f. T he t h i rd topic to be d i s c u s s ed is the i n t e r a c t i on b e t w e en c h e m i c a ls and e n z y m es a n d / or e n z y me s y s t e m s. We would l i ke to d e v e l op a p r e - e m e r g e n ce h e r b i c i de that is a c t i ve only on g e r- m i n a t i ng s e e d s. T h is p r e - e m e r g e n ce h e r b i c i de w o u ld not be a c t- i ve on r o o t s, s t e ms or l e a v es of e m e r g ed p l a n t s. J o n es and V a r n er (1967) h a ve d e s c r i b ed a b i o a s s ay f or g i b b e r e l l ic a c id u s- ing b a r l ey h a l f - s e e d s. One a d v a n t a ge of t h is t y pe of s y s t em t h at one w o u ld be studying the e f f e c ts of c h e m i c a ls on p r i or to the s t a rt of c e ll d i v i s i o n. is s e e ds I m p r o v i ng C o m p e t i t i ve A b i l i ty of T u rf P l a n ts O v er the p a st 20 y e a r s, i n f o r m a t i on h as b e en a c c u m u l a t i ng in the l i t e r a t u re w h i ch e n a b l es one to c l a s s i fy p l a n ts into e f f i c- i e nt p l a n ts and n o n - e f f i c i e nt p l a n ts a c c o r d i ng to t h e ir a b i l i ty to a s s i m i l a te C 02 ( B l a ck et a l ., 1969). T he photo s y n t h e t ic c h a r a c- t e r i s t i cs of e f f i c i e nt and n o n - e f f i c i e nt p l a n ts a re g i v en in T a b le 1. B l a ck et al. (1969) h a ve s u g g e s t ed that p l a n ts i ty to photo s y n t h e s i ze at high r a t es ( e f f i c i e nt plants) a re m o re c o m p e t i t i ve than t h o se with a l ow photo s y n t h e t ic c a p a c i ty (non- e f f i c i e nt p l a n t s ). S u ch p l a n ts as b e r m u d a g r a s s, c r a b g r a s s, c o r n, s o r g h u m, j o h n s o n g r a s s, s u g ar c a ne and p i g w e ed a re e x a m p l es of e f f i c i e nt p l a n t s, and a ll of t h e se a re v e ry c o m p e t i t i v e. K e n- t u c ky b l u e g r a s s, t a ll f e s c u e, w h e a t, o a t s, b a r l e y, r i c e, s o y b e a ns and s p i n a ch a re e x a m p l es of n o n - e f f i c i e nt p l a n t s. with the c a p a c- In o r d er to e m p h a s i ze the c o m p e t i t i ve n a t u re of e f f i c i e nt p l a n t s, the c o l u mn with the photo s y n t h e t ic c h a r a c t e r i s t i cs of e f f i c i e nt p l a n ts h as b e en l a b e l ed c r a b g r a ss and the c o l u mn f or n o n - e f f i c i e nt p l a n ts h as b e en l a b e l ed b l u e g r a s s. T h u s, the data g i v en in T a b le 1 a re r a n g es f or e f f i c i e nt and n o n - e f f i c i e nt plants T a b le 1. C h a r a c t e r i s t i cs of e f f i c i e nt and n o n - e f f i c i e nt p l a n t s. B l u e g r a ss C r a b g r a ss Light S a t u r a t i on 1000-3000 f t -c > 5000 f t -c CO2 A s s i m i l a t i on R a te 1 5 - 35 mg C O 2 / sq d m / hr 50-80 m g / sq d m / hr O p t i m um T e m p e r a t u re 1 0 0 - 2 5° C Photo r e s p i r a t i on P r e s e nt 3 0 ° - 4 0° C A b s e nt C o m p e n s a t i on P o i nt >30 p pm C O2 <5 p pm CC>2 and a re not s p e c i f ic f or c r a b g r a ss and K e n t u c ky b l u e g r a s s. W h i le l o o k i ng at T a b le 1, it should be r e m e m b e r ed that h e re i n t e n- in c e n t r al Ohio on a hot, b r i g ht s u m m er d a y, the light s i ty is a b o ve 8000 f t -c and the t e m p e r a t u re at l e a st 3 2 ° C. It c an be s e en f r om T a b le 1 that on a b r i g ht s u m m er d a y, both K e n t u c ky b l u e g r a ss and c r a b g r a ss a re light s a t u r a t e d; i . e ., t h ey both a re p h o t o s y n t h e s i z i ng at t h e ir m a x i m um r a t e. H o w- e v e r, it m u st be noted that c r a b g r a s s, the e f f i c i e nt plant, h as a m a x i m um r a te of C O2 a s s i m i l a t i on of 50-80 mg C 0 2 / sq dm of l e af a r ea p er h o u r, w h i le K e n t u c ky b l u e g r a s s, the n o n - e f f i- c i e nt plant, h as a m a x i m um r a te of only 1 5 - 35 mg C 0 2 / sq dm h r. Not only high light i n t e n s i t y, but a l so high t e m p e r a t u re f a v o rs the h i g h er r a t es of C O2 a s s i m i l a t i on of c r a b g r a ss o v er f or b l u e g r a s s, as c an be s e en in t h e ir o p t i m um t e m p e r a t u re p h o t o s y n t h e s i s. O n ce a g a i n, on a hot s u m m er d a y, 3 2 °C is the o p t i m um t e m p e r a t u re r a n ge f or e f f i c i e nt p l a n t s, w h i ch h a ve an o p t i m um t e m p e r a t u re of 3 0 ° - 4 0 ° C. S i n ce n o n - e f f i c i e nt p l a n ts h a ve a r a n ge of 1 0 ° - 2 5 ° C, a t e m p e r a t u re of 3 2 °C is a b o ve t h e ir o p t i m um t e m p e r a t u re and t h e ir r a te of C O2 f i x a- t i on w i ll be r e d u c ed b e c a u se of the e x c e s s i v e ly high t e m p e r a- in u r e. P h o t o r e s p i r a t i o n, w h i ch is an i n c r e a se in 02 uptake or C 02 r e l e a se u n d er c o n d i t i o ns of high light i n t e n s i ty and 02 a b o ve 2%, is p r e s e nt in n o n - e f f i c i e nt p l a n ts but is not p r e s e nt in e f f i c i e nt p l a n t s. P h o t o r e s p i r a t i on is a w a s t e f ul p r o c e s s. p l a n ts a re r e l e a s i ng C 02 without c o n s e r v i ng e n e r gy ( J a c k s on and V o l k, 1970). l e v e ls The A n o t h er c h a r a c t e r i s t ic of n o n - e f f i c i e nt p l a n ts is t h e ir c o m- p e n s a t i on point. T h e ir c o m p e n s a t i on point is a b o ve 30 p pm C 02, w h i le e f f i c i e nt plants h a ve a c o m p e n s a t i on point of l e ss than 5 p pm C 02. What this m e a ns is that, if you p l a ce c r a b g r a ss and K e n t u c ky b l u e g r a ss t o g e t h er in a c l o s ed s y s t e m, both g r a s s es w i ll f ix C 02 until the c o n c e n t r a t i on of C 02 in the c h a m b er r e a c h es the c o m p e n s a t i on point of K e n t u c ky b l u e g r a s s. A l t h o u gh the c r a b- g r a ss w i ll continue to f ix C 02 the K e n t u c ky b l u e g r a ss w i ll s t a rt to e v o l ve C 02, r e s u l t i ng in the death of the K e n t u c ky b l u e g r a s s. T he e f f e ct of light i n t e n s i ty on C 02 f i x a t i on is shown g r a p h- f i x- i c a l ly in F i g u re 1. F or n o n - e f f i c i e nt p l a n t s, the r a te of C 02 a t i on l e v e ls off and is c o n s t a nt f or light i n t e n s i t i es a b o ve 3000 f t - c. T he r a te of C 02 f i x a t i on f or e f f i c i e nt p l a n ts c o n t i n u es to i n c r e a se f or l i g ht i n t e n s i t i es g r e a t er than 5000 f t - c. Not only do e f f i c i e nt p l a n ts h a ve a h i g h er l e v el of light s a t u r a t i o n, but t h ey a l so h a ve m u ch h i g h er r a t es of C 02 a s s i m i l a t i on at a ll but the v e ry l o w e st l i g ht i n t e n s i t i e s. T h is f i g u re e m p h a s i z es the f a ct that, s u m m er d ay w h en the light i n t e n s i ty is at l e a st 8000 f t - c, c r a b- g r a ss c an c a p t u re v a s t ly m o re light e n e r gy than K e n t u c ky b l u e- g r a s s. on a b r i g ht A g r a p h ic p r e s e n t a t i on of the e f f e c ts of t e m p e r a t u re on C 02 in r a te a b o ve and b e l ow t h e se f i x a t i on is shown in F i g u re 2. T he r a te of C 02 f i x a t i on f or the n o n - e f f i c i e nt plant is r o u g h ly c o n s t a nt b e t w e en 1 5° and 2 5 ° C, w i th a d e c r e a se t e m p e r a t u r e s; w h i le the r a te of C 02 f i x a t i on f or e f f i c i e nt p l a n ts continues to i n c r e a se to a b o ve 4 0 ° C. Not only do e f f i c i e nt p l a n ts h a ve a m u ch h i g h er o p t i m um t e m p e r a t u re but, a g a i n, t h e ir r a te of C 02 a s s i m i l a t i on is m u ch g r e a t er at a ll but the l o w e st t e m p e r a t u r e s. On a b r i g ht s u m m er d ay with t e m p e r a t u r es a r o u nd 3 5 ° C, c r a b- g r a ss is f i x i ng C 02 at a m a x i m al r a t e. Due to the e x c e s s i v e ly h i gh t e m p e r a t u r e s, K e n t u c ky b l u e g r a ss is f i x i ng C 02 at a r e d u c ed Figure 1. General response of photosynthesis to i n c r e a s i ng i n t e n- s i ty of Adapted from Black et a l. l i g ht (1969). f or e f f i c i e nt and n o n - e f f i c i e nt p l a n t s. Temperature °C Figure 2. General response of photosynthesis to i n c r e a s i ng tem- perature from Black et a l. (1969). for e f f i c i e nt and n o n - e f f i c i e nt p l a n ts adapted r a t e. A f t er r e v i e w i ng the p h o t o s y n t h e t ic c h a r a c t e r i s t i cs of e f- f i c i e nt and n o n - e f f i c i e nt p l a n t s, it is v e ry e a sy to u n d e r s t a nd w hy c r a b g r a ss and p i g w e ed a re v e ry a b le c o m p e t i t o r s. T he d i f f e r e n c es in the p a t h w a ys of CC>2 f i x a t i on in e f f i c i e nt and n o n - e f f i c i e nt p l a n ts h a ve b e en r e v i e w ed by H a t ch and S l a ck (1970). N o n - e f f i c i e nt p l a n t s, s u ch as K e n t u c ky b l u e g r a s s, f ix C O2 by m e a ns of the r e d u c t i ve p e n t o se c y c le or C a l v in c y c l e. W h en 1 4C Oo is f ed to a n o n - e f f i c i e nt plant the f i r st C ing p r o d u ct is 3 - p h o s p h o g l y c e r a t e. H o w e v e r, w h en to an e f f i c i e nt plant s u ch as c r a b g r a s s, the f i r st C ^ - c o n t a i n i ng p r o d u c ts a re o x a l o a c e t a t e, m a l a te and a s p a r a t e. T he p a t h w ay of C O2 f i x a t i on in e f f i c i e nt p l a n t s, as p r o p o s ed by H a t ch and S l a ck (1970), is outlined in F i g u re 3. c o n t a i n- is f ed E f f i c i e nt p l a n ts h a ve two t y p es of c h l o r o p l a s t s. T h o se in the l a ck no s t a r ch bundle s h e a th c e l ls a r o u nd the v a s c u l ar t i s s ue a re l a r g e, g r a na and contain m a ny s t a r ch g r a i n s, w h i le t h o se in the m e s o- p h y ll c e l ls a re s m a l l e r, h a ve g r a na and contain f ew to g r a i ns ( L a e t s c h, 1968). By m e a ns of n o n - a q u e o us d e n s i ty f r a c- t i o n a t i o n, H a t ch and S l a ck (1970) h a ve i s o l a t ed t h e se two t y p es of c h l o r o p l a s ts f r om c o r n. T h ey h a ve shown that the m e s o p h y ll c h l o r o p l a s ts c o n t a in the C 4 - d i c a r b o x y l ic a c id c y c le e n z y m es and that the bundle sheath c h l o r o p l a s ts contain the C a l v in c y c le e n- z y m e s. A c c o r d i ng to the s c h e me p r o p o s ed by H a t ch and S l a c k, p y r u v a te r e a c ts with A TP and i n o r g a n ic phosphate to f o rm p h o s- p h o e n o l p y r u v a te ( P E P ). T he P EP a c e t a te w h i ch is r a p i d ly i n t e r c o n v e r t ed to m a l a te and a s p a r a t e. T he C 4 - c a r b o x yl of o x a l o a c e t a te is t r a n s f e r r ed to an a c c e p t or f r om the C a l v in c y c le and a p p e a rs as the C -l of 3 - p h o s p h o g l y- c e r a te ( 3 - P G A ). With this t r a n s c a r b o x y l a t i o n, p y r u v a te is r e g e n- e r a t ed f r om the C - l, C - 2, and C -3 c a r b o ns of o x a l o a c e t a te and the C 4 - d i c a r b o x y l ic a c id cy'cle is c o m p l e t e d. In the s e c o nd c y c l e, 3 - P GA is c o n v e r t ed to h e x o se p h o s p h a t es and then to s u c r o se and s t a r c h, w h i ch a re the end p r o d u c ts of p h o t o s y n t h e s i s. P a rt of the h e x o se p h o s p h a t es a re u s ed to r e g e n e r a te the C -4 c a r b o x yl a c- c e p t or w h i ch c o m p l e t es the C a l v in c y c l e. T h is a c c e p t or is e i t h er r i b u l o se d i p h o s p h a te or a C2 c o m p o u nd d e r i v ed f r om r i b u l o se d i p h o s p h a t e. is u t i l i z ed by e f f i c i e nt p l a n ts to f ix one m o l e c u le of C 02. It should be noted that one e x t ra m o l e c u le of A TP is c a r b o x y l a t ed to g i ve o x a l o- T h is F i g. 3. A proposed scheme for C^-dicarbcKylic acid pathway of p h o t o s y n t h e s i s. Adapted from Hatch and Slack (1970). input of e x t ra e n e r gy m ay be one of the r e a s o ns w hy p l a n ts with the C 4 - d i c a r b o x y l ic a c id c y c le a re a b le to f ix m o re C O 2. Not only do e f f i c i e nt p l a n ts f ix m o re CC>2> but t h ey a l so l a ck p h o t o r e s p i r a t i o n, w h i ch is an e n e r gy d e p l e t i ng p r o c e s s. M o st of the i n f o r m a t i on on p h o t o r e s p i r a t i on w as t a k en f r om the r e v i ew by J a c k s on and V o lk (1970). D u r i ng p h o t o r e s p i r a t i o n, O2 is t a k en up and C O2 is g i v en off. T he b i o c h e m i c al r e a c t i o ns in photo- r e s p i r a t i on and the o r g a n e l l es i n v o l v ed a re g i v en in F i g u re 4. G l y c o l a te is f o r m ed in the c h l o r o p l a s ts d u r i ng the p h o t o s y n t h e- t ic p r o c e ss but the m e c h a n i sm of its f o r m a t i on is not know. A f t er b e i ng s y n t h e s i z ed in the c h l o r o p l a s t s, f e r r ed to the p e r o x i s o m es w h e re it is O2 is r e d u c ed to h y d r o g en p e r o x i d e. T h is is the m e t a b o l ic step in p h o t o r e s p i r a t i on w h e re O2 is t a k en up. T he g l y o x y l a te then r e a c ts with g l u t a m a te to g i ve g l y c i ne and the g l y c i ne is s y n t h e s i z ed in the p e r o x i s o m e s, to the c y t o p l a sm w h e re t wo g l y c i n es a re c o m b i n ed to g i ve s e r- ine and CC>2. T h u s, the C O2 p r o d u c ed in p h o t o r e s p i r a t i on c o m es f r om the c a r b o x yl g r o up of g l y c i n e. o x i d i z ed to g l y o x y l a te and g l y c o l a te is t r a n s- - k e t o g l u a r a t e. A f t er it is t r a n s f e r r ed U s i ng t o b a c co l e af d i s c s, Z e l i t ch (1967) h as shown that it is p o s s i b le to inhibit p h o t o r e s p i r a t i on with c < - h y d r o x y - 2 - p y r i d i n e- m ethane s u l f o n ic a c i d. T h is c o m p o u nd is an i n h i b i t or of g l y c o- l a te o x i d a s e. T h is s u g g e s ts p o t e n t i al f or c o n v e r t i ng e f f i c i e nt to n o n - e f f i c i e nt p l a n ts w h i ch m ay a l t er c o m p e t i t i ve s t a t u s. We would l i ke to d e v e l op t e c h n i q u es f or m a k i ng n o n - c o m- p e t i t i ve p l a n ts l i ke K e n t u c ky b l u e g r a ss m o re c o m p e t i t i v e; or c o n v e r s e l y, f or m a k i ng c o m p e t i t i ve p l a n ts l i ke c r a b g r a ss c o m p e t i t i v e. One w ay would be to d e v e l op a c h e m i c al w h i ch w o u ld inhibit p h o t o r e s p i r a t i on without being p h y t o t o x i c. A n o t h er w ay w o u ld be to look f or p l a n ts with e i t h er r e d u c ed p h o t o r e s p i- r a t i on or w i th a h i g h er net r a te of p h o t o s y n t h e s i s. We plan to l o ok f or b i o t y p es within a s p e c i es w h i ch h a ve r a t o ry r a te on a h i g h er net photo s y n t h e t ic r a t e. If t h e se b i o- t y p es c an be found, t h ey w i ll be i n c l u d ed in our b r e e d i ng p r o- g r a m. l e ss a l o w er p h o t o r e s p i- Figure 4. A proposed scheme f or the biochemical r e a c t i o ns p h o t o r e s p i r a t i o n. Adapted from Jackson and Volk involved (1970). in C h e m i c a l / G e n o t y pe I n t e r a c t i o ns P l a nt b r e e d e rs h a ve f or m a ny y e a rs u s ed v a r i a t i on b a s ed on g e n e t ic r e c o m b i n a t i on f or t a i l o r i ng p l a n ts to f it n u m e r o us u s es and e n v i r o n m e n t al c o n d i t i o n s. W h i le this b i o l o g i c al p h e n o- m e na is v e ry e s s e n t i al in plant b r e e d i n g, it is now l e a d i ng to p r o b l e ms in the a r ea of w e ed c o n t r o l. H e t e r o z y g o us populations of w e ed p l a n ts a r i s i ng f r om n ew g e n e t ic r e c o m b i n a t i o ns a re p r o- d u c i ng p l a n ts that p o s s e ss r e s i s t a n ce to g i v en h e r b i c i d es that e a r l i er w e re e f f e c t i ve in c o n t r o l l i ng s u ch plant c a t e g o r i e s. H a r p er (1956) h as r e v i e w ed the p o t e n t i al f or d e v e l o p m e nt of w e e ds i n v e s t i- tant to h e r b i c i d e s. F or s p e c i f ic w e ed s p e c i e s, s e v e r al g a t o rs h a ve r e p o r t ed ( R y d r y ch and S e e l y, 1964; S a n t l e m a nn and M e a d e, 1961) on v a r i a t i on in r e s i s t a n ce to h e r b i c i d es within and b e t w e en s p e c i e s. R y d r y ch and S e e ly (1964) h a ve shown m a r k ed v a r i a t i on in l i n es of w i ld o a ts to p r o p h a m. V a r i a t i on in the s u s- c e p t i b i l i ty of the s p e c i es S e t a r ia l u t e s c e ns and S. f a b e r ii to d a l- a p on h as b e en studied by S a n t l e m a nn and M e a de (1961). r e s i s- S e l e c t i on p r e s s u re a r i s i ng f r om continuous h e r b i c i de a p p l i- c a t i on t e n ds to i s o l a te n ew r e s i s t a nt g e n o t y p e s. T h e se t y p es a re t h en s e l e c t i v e ly f a v o r ed by f u r t h er u se of the s a me h e r b i c i d e. r e c e s s i ve G e n e t i c a l ly c o n t r o l l ed m e c h a n i s ms e f f e c t i ng r e s i s t a n ce or s u s c e p t i b i l i ty of s o me c r op p l a n ts h a ve b e en studied in s o me d e- t a il by H a m i l t on (1964). He r e p o r t ed that r e d u c t i on in t o l e r a n ce of c o rn to a t r a z i ne w as a s s o c i a t ed with h o m o z y g o us s e g r e g a t e s, w h i ch a re l ow in b e n z o x a z i n o n e. T he b e n z o x a z i n o ne d e r i v a t i ve in the l e ss t o l e r a nt c o rn line w as found to be c o m p a r- a b le to that found in w h e at ( H a m i l t on and M o r e l a n d, 1962); h o w- e v e r, the c o rn line did not show the a c u te t o x i c i ty of w h e a t. A d i f f e r e nt g e n e t i c a l ly c o n t r o l l ed m e c h a n i sm a p p e a rs to be f u n- c t i o n i ng in s o r g h u m, w h i ch h as r e l a t i v e ly good t o l e r a n ce to s i- m a z i n e. Y et it d o es not contain b e n z o x a z i n o ne d r i v a t i v es and e x c i s ed r o o ts do not c o n v e rt s i m a z i ne to h y d r o x y s i m a z i n e, as is the c a se of t o l e r a nt l i n es of c o r n. A c u te t o x i c i ty m ay be r e- l a t ed to p h o t o o x i d a t i o ns or a c c u m u l a t i on of an oxidant as a r e- sult of H i ll r e a c t i on inhibition, a c c o r d i ng to H a m i l t on (1964). He f u r t h er s u g g e s t ed that s i n ce c a r o t e n o i ds s e em to p l ay a r o le in p r e v e n t i ng h a r m f ul p h o t o o x i d a t i o n, t h ey m i g ht be i n v o l v ed in r e s i s t a n ce of c o rn to s i m a z i n e. O t h er r e p o r ts ( C a s t e l f r a n c o, F oy and D e u t s c h, 1 9 6 1; G y s in and K n i i s l i, I960; H a m i l t o n, 1964; Roth, 1 9 5 7; Roth and K n i i s l i, 1961) f u r t h er d e t a il r e s u l ts of b i o c h e m i- c al m e c h a n i s ms o p e r a t i ng in the c o r n - t r i a z i ne c a s e. V e ry p r e l i m i n a ry t e s ts h a ve b e en c a r r i ed out in our l a b o r- a t o r i es to a s s e ss the r e a c t i on of a c c e s s i o ns of K e n t u c ky b l u e- g r a s s, St. A u g u s t i n e g r a ss and b e r m u d a g r a ss to h e r b i c i d e s. b le 2 s h o ws the v a r i a t i on in s e v e r al a c c e s s i o ns of K e n t u c ky b l u e- g r a ss to l i n u r o n. S i g n i f i c a nt d i f f e r e n c es in r e s p o n se w e re noted. W h en a c c e s s i on r e s p o n se to a t r a z i ne w as e v a l u a t e d, the m a g n i- tude of v a r i a t i on w as m u ch l e ss than f or l i n u r o n, as shown in T a b le 3. S i m i l ar v a r i a t i on in a c c e s s i on r e s p o n se of St. A u g u s- t i n e g r a ss and b e r m u d a g r a ss w as noted. T a- T a b le 2. G e n o t y p e / h e r b i c i de p r a t e n s i s. i n t e r a c t i on on a c c e s s i o ns of P oa A c c e s s i o ns Ba 6 3 - 1 48 Ba 6 3 - 1 51 Ba 6 3 - 68 * L i n u r on at 10#/A P e r c e nt K i l l* 97 50 0 T a b le 3. G e n o t y p e / h e r b i c i de p r a t e n s i s. i n t e r a c t i on on a c c e s s i o ns of P oa A c c e s s i o ns Ba 6 7 - 2 42 Ba 6 2 - 31 Ba 6 7 - 2 47 * A t r a z i ne 1 0 # /A P e r c e nt K i l l* 1 00 90 80 C o n c l u s i o ns f r om t h is p r e l i m i n a ry w o rk a re s u f f i c i e n t ly e n- c o u r a g i ng to w a r r a nt f u r t h er attention to r e s e a r ch in this a r e a. A s e c o nd p h a se w i ll e v a l u a te h y b r i ds d e v e l o p ed f r om s u s c e p t i b le and r e s i s t a nt a c c e s s i o n s. C h e m i c a l - E n z y me I n t e r a c t i o ns T he t h i rd unique a p p r o a ch to w e ed c o n t r ol is the study of the i n t e r a c t i on b e t w e en c h e m i c a ls and s p e c i f ic e n z y m es a n d / or e n- z y me s y s t e m s. An e x a m p le of the type of i n t e r a c t i on that we a re i n t e r e s t ed in is the e f f e c ts of c h e m i c a ls on the i n i t i al s t e ps of g e r m i n a t i o n. T he idea behind this type of study is to d e v e l op a h e r b i c i de that h as only p r e - e m e r g e n ce a c t i v i ty and a t t a c ks m e t a- b o l ic r e a c t i o ns c o m m on only to the g e r m i n a t i on p h a se of g r o w t h. S o me p r e - e m e r g e n ce h e r b i c i d es a re m i t o t ic i n h i b i t o r s, and t h ey inhibit the r o ot g r o w th of p l a n ts as w e ll as the e m e r g e n ce of s e e d- l i n g s. A h e r b i c i de that is s p e c i f ic f or s o me b i o c h e m i c al r e a c t i on or r e a c t i o ns in the i n i t i al s t a g es of g e r m i n a t i on p r i or to c e ll d i v i- s i o n, p r o b a b ly would not h a ve h e r b i c i d al a c t i v i ty on g r o w i ng p l a n t s. As shown in F i g u re 5, the b a r l ey h a l f - s e ed b i o a s s ay f or g a 3, as d e s c r i b ed by J o n es and V a r n er (1967), is an e x a m p le of this t y pe of a t e st s y s t e m. In the b a r l ey h a l f - s e ed b i o a s s a y, the d i s t al end of the b a r l ey s e ed is i n c u b a t ed in a c u l t u re solution containing G A ^. T he amount of ^ - a m y l a se p r o d u c ed in the b a r l ey h a l f - s e ed is d i r e c t ly p r o p o r t i o n al to the c o n c e n t r a t i on of G A3 in the m e d i u m. In the study of the e f f e c ts of c h e m i c a ls on the g e r m i n a- t i on of s e e d s, both a h a l f - s e ed and a w h o l e - s e ed b i o a s s ay s y s t em w o u ld be u s e d. Both h a l f - s e e ds and w h o l e - s e e ds would be b a t ed in c u l t u re m e d ia with and without the c h e m i c al of as w e ll as with and without g a 3. w o u ld be e x t r a c t ed f r om the s e e ds and then the a m o u nt of e n z y me e x t r a c t ed a s s a y e d. A f t er i n c u b a t i o n, the K - a m y l a se c u l t u re i n c u- i n t e r e s t, P e n n er (1968) s h o w ed that b e n z y l a d e n i ne s t i m u l a t ed the s y n- t h e s is of ^ - a m y l a se in e x c i s ed c o t y l e d o ns of s q u a s h; w h e r e a s, g a3 had no e f f e c t. T he u se of both s q u a sh and b a r l ey in a b i o a s s ay f or c h e m i c al e f f e c ts a p p e a rs to be d e s i r a b le s i n ce e n z y me s y n t h e- s is is p r o m o t ed in one by c y t o k i n n i n s, and in the o t h er by g i b b e r- e l l i n s. A l s o, s i n ce s q u a sh s e e ds contain a l a r ge amount of oil, F i g u re 5. A p r o p o s ed b i o - a s s ay p r o c e d u re f or studying a c t i o ns of c h e m i c a ls and e n z y me s y s t e ms i n t e r- in s e ed g e r m i n a t i o n. B i o - a s s ay s y s t em S t e ps W h o le s e ed Half s e ed T r e at with c h e m i c al I n c u b a te E n z y me e x t r a ct E n z y me a s s ay X X X X X X X X t h ey a re not dependent on s t o r ed c a r b o h y d r a t es f or g r o w t h. E i t h er of the a b o ve two d i f f e r e n c es m ay e x p l a in w hy s q u a sh s e e ds a re t o l e r a nt to c h l o r a m b e n, w h i le b a r l ey s e e ds a re not. If c h e m i c a l ly t r e a t ed s e e ds l a ck K - a m y l a se a c t i v i t y, t h e re a re t h r ee p o s s i b le r e a s o ns f or this l a ck of a c t i v i t y. One, the c h e m i c al is an i n h i b i t or of <<-amylase. T w o, the c h e m i c al is inhibiting the s y n t h e s is of <=<-amylase by inhibiting e i t h er or p r o t e in s y n t h e s i s. Or t h r e e, the c h e m i c al is inhibiting the s y n t h e s is of the p h y t o h o r m o ne by the e m b r y o. R NA H o p e f u l l y, this type of b i o a s s ay s y s t em would y i e ld a h i g h ly s e l e c t i ve p r e - e m e r g e n ce h e r b i c i de that would p r e v e nt the g e r m i n- a t i on of s e e d s, but would not a f f e ct m a t u re p l a n t s. T h is s e l e c t i ve p r e - e m e r g e n ce h e r b i c i de would not a f f e ct the v i g or of the g r a ss p l a n ts in an e s t a b l i s h ed l a w n, n or would it a f f e ct the e s t a b l i s h- m e nt of a l a wn u s i ng sod. By e l i m i n a t i ng the g e r m i n a t i on of w e ed s e e d s, s u ch as c r a b g r a s s, the d e s i r a b le t u r f g r a s s es would be m o re c o m p e t i t i v e. R e f e r e n c es C i t ed B l a c k, C. C ., T. M. C h en and R. H. B r o w n. 1969. B i o c h e m i- c al B a s is f or P l a nt C o m p e t i t i o n. W e ed S c i e n ce 17: 338- 334. C a s t e l f r a n c o, P ., C. L. F oy and D e b o r ah B. D e u t s c h. N o n e n z y m a t ic d e t o x i f i c a t i on of 2 - c h l o r o - 4 , 6 - b is m i n o ) - s - t r i a z i ne ( s i m a z i n e) by e x t r a c ts of Z ea M a y s. W e e ds 9: 5 8 0 - 5 9 1. 1 9 6 1. ( e t h y l a- G y s i n, H. and E. K n i i s l i. I960. C h e m i s t ry and h e r b i c i d al p r o- p e r t i es of t r i a z i ne d e r i v a t i v e s. A d v a n c es in p e st c o n t r ol r e s e a r ch 3: 289-358. I n t e r s c i e n c e, N ew Y o r k. H a m i l t o n, R. H. 1964. A c o rn m u t a nt d e f i c i e nt in 2 , 4 - d i h y d r o- x y - 7 - m e t h o x y - 1 , 4 - b e n z o x a z i n - 3 - o ne with an a l t e r ed t o l e r- a n ce of a t r a z i n e. 12: 2 7 - 3 0. H a m i l t o n, R. H. and D. E. M o r e l a n d. 1962. S i m a z i n e: D e g r a- dation by c o rn s e e d l i n g s. S c i e n ce 135: 3 7 3 - 3 7 4. H a r p e r, J. C. 1956. The e v o l u t i on of w e e ds in r e l a t i on to h e r- b i c i d e s. P r o c. B r i t. W e ed C o n t r. Conf. 3: 1 7 9 - 1 8 8. H a t c h, M. P. and C. R. S l a c k. 1970. P h o t o s y n t h e t ic C C >2- F i x- ation P a t h w a y s. Ann. R e v. P l a nt P h y s i o l o gy 21: 1 4 1 - 2 1 4. J a c k s o n, W. A. and R. J. V o l k. 1970. P h o t o r e s p i r a t i o n. Ann. R e v. P l a nt P h y s i o l o g y . 2 1: 3 8 5 - 4 3 2. J o n e s, R. L,. and J. E. V a r n e r. 1967. T he B i o a s s ay of G i b b e r- e l l i n s. P l a n ta 72: 1 5 5 - 1 6 1. L a e t s c h, W. M. 1968. C h l o r o p l a st S p e c i a l i z a t i on in D i c o t y l e d o ns P P o s s e s s i ng the C 4 - D i c a r b o x y l ic A c id P a t h w ay of P h o t o- s y n t h e t ic C 02 F i x a t i o n. A m e r. J. B o t. 55: 87 5-883. P e n n e r, Donald. 1968. H e r b i c i d al I n f l u e n ce on A m y l a se in B a r- l ey and S q u a sh S e e d l i n g s. W e ed S c i e n ce 16: 5 1 9 - 5 2 2. R o t h, W. 1 9 5 7. E t u de c o m p a r ée de la r e a c t i on de m a is et du B le a la S i m a z i n e, s u b s t a n ce h e r b i c i d e. C o m p t es R e n d u s. L A c a d e m ic d es S c i e n c es 245: 942-944. R o t h, W. and E. K n i i s l i. 1 9 6 1. B e i t r ag z ur K e n n t n is d er R e s- i s t e n z p h a n o m e ne e i n z e l n er P f l a n z en g e g e n i i er den p h y t o- t o x i s c h en W i r k s t a ff S i m a z i n. E x p e r i e n t ia 17: 3 1 2 - 3 1 3. R y d r y c h, D. J. and C. I. S e e l y. 1964. E f f e ct of I PC on s e l e c- t i o ns of w i ld o a t s. W e e ds 12: 2 6 5 - 2 6 7. S a n t l e m a n n, P. W. and J. A. M e a d e. 1 9 6 1. V a r i a t i on in m o r- p h o l o g i c al c h a r a c t e r i s t i cs and d a l a p on s u s c e p t i b i l i ty w i t h- in the s p e c i es S e t a r ia l u t e s c e ns and S. f a b e r i i. W e e ds 9: 4 0 6 - 4 1 0. Z e l i t c h, I s r a e l. 1967. W a t er and C O2 T r a n s p o rt in the P h o t o- in H a r v e s t i ng the Sun, 232-248. E d s. s y n t h e t ic P r o c e ss San P e d r o, A ., G r e e r, F. A ., and A r m y, T. J. A c a d e m ic P r e s s, N ew Y o r k. D i s c u s s i on P e r i od D r. S c h m i d t: On what b a s is do you c l a im that the l ow p h o t o r e s p i- r a t i on w o u ld n e c e s s a r i ly be b e n e f i c i a l? er w h e re it m ay be an a d v a n t a ge to h a ve a plant that is photo- r e s p i r a n t. I c an s ee in c o ld w e a t h- I 'm not t a l k i ng about d a rk r e s p i r a t i o n. D u r- M r. S t o t t l e m y e r: ing p h o t o r e s p i r a t i on the plant is r e l e a s i ng C O2 without c o n s e r v- ing e n e r g y, and t h is is an i n e f f i c i e nt p r o c e ss w h i ch one would think is d e t r i m e n t al to the plant. If the plant d o e s n 't r e s p i r e, t h en C O2 i s n 't r e l e a s ed and e n e r gy is c o n s e r v e d. T he plant c an a l w a ys s t o re e x c e ss f i x ed c a r b on as s t a r c h. What would you s u g g e st is the a d v a n t a ge of p h o t o r e s p i r a t i on to the p l a n t? D u r i ng r e s p i r a t i on in f a t ty s e e d s, the f a t ty a c i ds a re b r o k en d o wn into a c e t a te and t h is a c e t a te is u t i l i z ed v ia the g l y o x y l a te c y c l e, w h i ch is e s s e n t i a l ly a m o d i f i ed c i t r ic a c id c y c l e. Is this the g l y o x y l a te p a t h w ay that y ou a re thinking of? T h is is a d i f- f e r e nt s y s t e m. D r. S c h m i d t: T he point that I want to m a ke is that in g r a s s e s, s u ch as b l u e g r a s s e s, w h i ch is d e f i n i t e ly a p h o t o r e s p i r a t o r, you w i ll h a ve a b u i l d - up of c a r b o h y d r a t es in s p i te of the f a ct that y ou m ay h a ve an i n c r e a se of p h o t o r e s p i r a t i o n, e v en during cold w e a t h e r. So this w o u ld be c o n t r a ry to the f a c t. I think we h a ve to be c a r e f ul w h en we l a b el t h is as being d e t r i m e n t a l. We m ay w a nt to s e l e ct g r a s s es that h a ve l ow p h o t o r e s p i r a t i o n, but a g a in t h ey m u st be e c o l o g i c a l ly adapted. is M r. S t o t t l e m y e r: T he m a in d i s a d v a n t a ge of p h o t o r e s p i r a t i on that it is m o st e v i d e nt w h en y ou h a ve l ow C O2 and high t e m p e r- a t u r e s. H i gh t e m p e r a t u r es a re a p r o b l em in the s u m m e r t i m e. It a p p e a rs that high t e m p e r a t u r es a re the p r o b l em w h en one t r i es to g r ow K e n t u c ky b l u e g r a ss and St. L o u i s. B l u e g r a s s es j u st f a de out in t h e se a r e as in the s u m m e r t i m e. s u p p l y, then it m ay be m o re c o m p e t i t i ve and b e t t er a b le to c o m- p e te w i th s u ch p l a n ts as b e r m u d a g r a ss and c r a b g r a s s, w h i ch a re e f f i c i e nt p l a n t s. If you c an get a plant that d o e s n 't w a s te i ts e n e r gy in s u ch p l a c es as W a s h i n g t o n, D. C. D r. S c h m i d t: At l o w er t e m p e r a t u r e s, the r e s p i r a t i on in light e x c e e ds that in d a r k, but at t e m p e r a t u r es a b o ve 4 0 C ., the r e- v e r se is t r u e. We h a ve to look at two b a s e s - - n ot only photo- r e s p i r a t i o n, but a l so p h o t o s y n t h e s i s. C O2 c o m p e n s a t i on point is dependent upon both f a c t o r s. Is p h o t o r e s p i r a t i on the l i m i t i ng f a c t or that we D r. L e d e b o e r: i n c r e a se h a ve on the c o ol s e a s on g r a s s e s; the f a ct that t h ey do t h e ir p h o t o r e s p i r a t i on d u r i ng high t e m p e r a t u r e? T he c o m p e n- s a t i on point g o es up so high that we l o se due to this f a c t. w o u ld h a ve to a g r ee with M r. S t o t t l e m y e r. S i n ce p h o t o r e s p i r a- tion t a k es p l a ce to t h is d e g r e e, it c an p r o b a b ly be e a r m a r k ed as a b e n e f i c i al p r o c e ss h e re if the p h o t o r e s p i r a t i on is r a t h er low. I don!t think we c an find p l a n ts a m o ng c o ol s e a s on g r a s s es w h e re it is c o m p l e t e ly a b s e n t. I Ifm t r y i ng to point out that you h a ve to look at the D r. S c h m i d t: r a t io b e t w e en p h o t o s y n t h e s is and p h o t o r e s p i r a t i o n. N u g g e t, f or e x a m p l e, w h i ch is a n o r t h e rn e c o t y p e, we find doing quite w e ll f or us in hot t e m p e r a t u r es and y et t h is g r a ss h as a v e ry high p h o t o r e s p i r a t i on r a t e. On the o t h er hand, it h as a high p h o t o- s y n t h e ic r a t e. So you h a ve l ow c o m p e n s a t i on point on t h is b a s i s. If y o u!re going j u st with p h o t o r e s p i r a t i on r a t e, t h is d o e s nft f it the t r e n d. T he point I!m t r y i ng to m a ke is that you h a ve to look at both f a c t o r s. D r. L e d e b o e r: To expand this a l i t t le f u r t h er into m a n a g e m e nt of t h e se g r a s s e s, h a ve you s p e c u l a t ed at a ll into m a n a g e m e nt p r a c t i c es w h i ch c an l o w er the p h o t o r e s p i r a t i on r a te of t h e se g r a s- s e s? H a ve you found any e v i d e n ce to t h i s? In D r. S c h m i d tfs w o rk w i th t h e se g r a s s e s, I b e l i e v e, that t h ey a b s o rb m o st of t h e ir n u t r i- e n ts d u r i ng c o o l er t e m p e r a t u r es and, as s u c h, i n c r e a se the a m o u nt of s t o r ed h y d r o c a r b o h y d r a t e s, t h e se c a r b o h y d r a t es Is t h e re a ny e v i d e n ce to t h is e f f e ct in the s e a r ch that you m a d e? in s u ch a m a n n er as the e n v i r o n m e nt d i c t a t e s. l a t er l e t t i ng the g r a ss m e t a b o l i ze h a ve I m u st point out that, at the p r e s e nt t i m e, w e ' ve M r. S t o t t l e m y e r: j u st m a de s o me p r e l i m i n a ry s t u d i es on C O¿ a s s i m i l a t i o n. E v i- d e n t a l ly D r. S c h m i dt h as done a lot m o re w o rk in this a r ea than we h a v e. A l t h o u gh we h a v e n 't gotten h e a v i ly i n v o l v ed in this w o r k, we a re d e f i n i t e ly planning to s t a rt in the n e ar f u t u r e. P E R S I S T E N CE A ND D E G R A D A T I ON OF C O M M O N LY U S ED T U RF H E R B I C I D ES IN OUR E N V I R O N M E NT D. D. K a u f m an S o il M i c r o b i o l o g i st P l a nt S c i e n ce R e s e a r ch D i v i s i on A g r i c u l t u r al R e s e a r ch S e r v i ce U. S. D e p a r t m e nt of A g r i c u l t u re B e l t s v i l l e, M a r y l a nd 20705 I n t r o d u c t i on M a ny p e s t i c i d es a re r e l e a s ed into o ur e n v i r o n m e nt to c o n- t r ol w e e d s, plant p a t h o g e ns and i n s e c t s. P a r ts of a ll p e s t i c i d es e n t er into the e n v i r o n m e nt and b e c o me an i n t e g r al p a rt of it. T h e r e f o r e, k n o w l e d ge of the b e h a v i or and p e r s i s t e n ce of a ll p e s t i c i d es sound and s a fe p e st c o n t r ol p r a c t i c e s. in o ur e n v i r o n m e nt is e s s e n t i al if we a re to d e v e l op N e a r ly a ll p e s t i c i d es a p p l i ed to our e n v i r o n m e nt u l t i m a t e ly r e a ch the s o i l. W h en a p e s t i c i de c o m es in c o n t a ct with the s o i l, s e v e r al p r o c e s s es m ay a ct to b r i ng about its d i s s i p a t i on f r om s o i l. G e n e r a l l y, o r g a n ic p e s t i c i d es a re d i s s i p a t ed m o re r e a d i ly than i n o r g a n i c s, although s o me e x c e p t i o ns p r o b a b ly e x i st (Sheets, 1964b). P r o c e s s es k n ow to d e c r e a se the c o n c e n t r a t i o ns of p e s t i- c i d es i n c l u de the f o r m a t i on of i n s o l u b le c o m p o u n ds and c o m p l e x e s, l e a c h i n g, dilution in s o i l, m e c h a n i c al r e m o v al (wind, w a t er and p l a n t s ), f i x a t i on and a d s o r p t i on to s o i l, m i c r o b i al d e g r a d a t i o n, p h o t o d e c o m p o s i t i o n, c h e m i c al r e a c t i o ns and v o l a t i l i z a t i o n. One of the c o n t r o v e r s i al a s p e c ts of our p r e s e nt e n v i r o n m e n t al s i t u a t i on c o n c e r ns the continued u se of p e s t i c i d e s. T he c h l o r i- n a t ed h y d r o c a r b on i n s e c t i c i d es h a ve c o me u n d er s e v e re c r i t i c i sm due to t h e ir r e l a t i v e ly long p e r s i s t e n ce m a g n i f i c a t i on t h r o u gh c e r t a in o r g a n i s ms and t h e ir f r e q u e nt d e t e c- t i on in the f o od chain. r e c e i v ed r e l a t i v e ly l i t t le c r i t i c i s m, until r e c e n t l y, p r i m a r i ly due to t h e ir l ow m a m m a l i an t o x i c i ty and s h o rt p e r s i s t e n ce u n d er In c o n t r a s t, the o r g a n ic h e r b i c i d es h a ve in the e n v i r o n m e n t, b i o- m o st c o n d i t i o n s. T he p u r p o se of this p r e s e n t a t i on is to e x a m i ne t he p e r s i s t e n ce and d e g r a d a t i on of c o m m o n ly u s ed t u rf h e r b i- c i d es in o ur e n v i r o n m e n t. T he c r i t e r ia f or s e l e c t i on of the h e r- b i c i d es d i s c u s s ed in this p r e s e n t a t i on w e re i n c l u d ed in r e f e r e n c es (Anon, 1968a; Anon, 1968b) and f r om p e r- s o n al o b s e r v a t i on of the author as to what w as a v a i l a b le on the s h e l v es of s e v e r al l o c al e m p o r i a. C o m m on and c h e m i c al n a m es of t h e se h e r b i c i d es a re p r e s e n t ed in T a b le 1. r e c o m m e n d a t i o ns T a b le 1. C o m m on and C h e m i c al N a m es of T u rf H e r b i c i d es D i s- c u s s ed in T e xt C o m m on N a me C h e m i c al N a me a t r a z i ne 2 - c h l o r o -4 - e t h y l a m i no - 6 - i s op r o p l a m i no - s - t r i a z i ne b e n e f in N - b u t y l - N - e t h y l - ^ < * | ° ^ t r i f l u r o - 2 , 6 - d i n i t r o- p - t o l u i d i ne b e n s u l i de 0 , 0 - d i i s o p r o p hy p h o s p h o r o d i t h i o a te S- e s t er with N - ( 2 - m e r c a p t o e t h y l) b e n- z e ne s u l f o n a m i de b r o m o x y n il 3,5 - dib r o mo - 4 - hyd r o x y b e n z o n it r ile c a c o d y l ic a c id h y d r o x y d i m e t h y l a r s i ne oxide 2 , 4 -D d a l a p on D C PA d i c a m ba ( 2 , 4 - d i c h l o r o p h e n o x y) a c e t ic a c id 2 , 2 - d i c h l o r o p r o p i o n ic a c id d i m e t h yl t e t r a c h l o r o t e r e p h t h a l a te 3 , 6 - d i c h l o r o - o - a n i s ic a c id 2 , 4 - D P, d i c h l o r p r op 2 - ( 2 , 4 - d i c h l o r o p h e n o x y) p r o p i o n ic a c id D M PA ^ 0 - ( 2 , 4 - d i c h l o r o p h e n y l ) £ - m e t h yl i s o p r o p y l p h o s p h o r a m i d o t h i o a t e] T a b le 1. Continued. C o m m on N a me C h e m i c al N a me D M T T, d a z o m et t e t r a h y d r o - 3 , 5 - d i m e t h y l - 2 H - 1 , 3 , 5- D S MA M A MA M C PA t h i a d i a z i n e -2 - t h i o ne d i s o d i um m e t h a n e a r s o n a te m o n o a m m o n i um m e t h a n e a r s o n a te ( 4 - c h l o r o - o - t o l y l ) o xy a c e t ic a c id m e t h yl b r o m i de m e t h yl b r o m i de M S MA n e b u r on p a r a q u at P MA m o n o s o d i um m e t h a n e a r s o n a te 1 - b u t y l - 3 - ( 3 , 4 - d i c h l o r o p h e n y l) -1 - m e t h y l u r ea 1 , 1 ' - d i m e t h y l - 4 , 41 - b i p y r i d i n i um s a l ts (aceto) p h e n y l m e r c u ry p o t a s s i um c y a n a te p o t a s s i um c y a n a te s i d u r on s i l v ex 1 - ( 2 - m e t h y l c y c l o h e x y l) - 3 - p h e n y l u r ea 2 - ( 2 , 4 , 5 - t r i c h l o r o p h e n o x y) p r o p i o n ic a c id s i m a z i ne 2 - c h l o r o - 4 , 6 - b i s ( e t h y l a m i n o) - s - t r i a- z i ne S M D C, m e t h am s o d i um m e t h y l d i t h i o c a r b a m a te 2 , 4 , 5 -T t e r b u t ol ( 2 , 4 , 5 - t r i c h l o r o p h e n o x y ) a c e t ic a c id 2 , 6 - d i - t e r t - b u t y l - p - t o l yl m e t h y l c a r b a- m a te P e r s i s t e n ce T he i m p o r t a n ce of a p r o c e ss in c a u s i ng the d i s s i p a t i on of a is l a r g e ly I n a c t i v a t i on or d e c o m p o s i t i on of a p e s t i c i d e, p e s t i c i de f r om s o il d e p e n ds on the p h y s i c al and c h e m i c al p r o- p e r t i es of the p e s t i c i d e, s o il p r o p e r t i es and p r e v a i l i ng e n v i r o n- m e n t al c o n d i t i o n s. w h i ch is a c t i ve f or only a f ew d a ys to a f ew w e e k s, a t t r i b u t a b le to a s i n g le p r o c e ss ( S h e e t s, 1964b). A d s o r p t i on of s o me p e s t i c i d es to s o il p a r t i c u l a te m a t t e r, f or e x a m p l e, is r a p id and s u f f i c i e n t ly c o m p l e te to r e n d er t h em i m m e d i a t e ly a c t i ve w h en t h ey e n t er the s o i l. S o me p e s t i c i d es d i s a p p e ar f r om s o il within a f ew d a ys to a f ew w e e ks by v o l a t i l i z a t i on or by c h e m i c al r e a c t i o ns and s u b s e q u e nt v o l a t i l i z a t i o n. D e g r a d- a t i on by s o il m i c r o o r g a n i s ms and l e a c h i ng f r om s o il m ay a c- count f or d i s s i p a t i on of a m a j or p a rt of s o me p e s t i c i d es that d i s a p p e ar r a p i d l y. T he l o n g er a p e s t i c i de p e r s i s t s, the g r e a t er the p r o b a b i l i ty that s e v e r al p r o c e s s es b e c o me i n v o l v ed in its i n a c t i v a t i on and d i s a p p e a r a n ce f r om s o il ( S m a ll and M c C a n t s, 1962). T he r e l a t i ve p e r s i s t e n ce of the c o m m o n ly u s ed t u rf h e r- b i c i d es is i l l u s t r a t ed in F i g u re 1. in- Figure 1. Average p e r s i s t e n ce of t u r f g r a ss h e r b i c i d e s. (The the average p e r s i s t e n ce p e r i o d; s o l id bar r e p r e s e n ts the thatched bar r e p r e s e n ts e x c e p t i o n al periods of These averages are based s o l e ly on a p e r s i s t e n c e. broad in- d i c a t i ve of any s i n g le s o il l i t e r a t u re survey and a r e, t h e r e f o r e, not t y p e ). D e g r a d a t i on M i c r o b i o l o g i c a l, c h e m i c a l, p h o t o c h e m i c al and p h y s i c al r e a c t i o ns a re a c t i ve in the d e c o m p o s i t i on of m a ny p e s t i c i d e s. F r ee of the s o il e n v i r o n m e n t, m i c r o b i al r e a c t i o ns c an be stud- i ed in d e t a il at the c e l l u l ar and e n z y m ic l e v e l s. I n v e s t i g a t i o ns w i th s t e r i le s o i ls and m o d el s y s t e ms h a ve r e v e a l ed that p u r e ly c h e m i c al s y s t e ms a l so p l ay a r o le in d e c o m p o s i ng p e s t i c i d e s. E x t e n s i ve i n v e s t i g a t i o ns of r e p r e s e n t a t i ve c o m p o u n ds within a p a r t i c u l ar g r o up of p e s t i c i d es h a ve e l u c i d a t ed c e r t a in c l a s s es of r e a c t i o ns w h i ch h a ve u n d e r l y i ng s i m i l a r i t i es f r om a c h e m- i c al and b i o c h e m i c al standpoint. u n d e r s t a n d i ng of t h e se r e a c t i o ns h as a l l o w ed us to p r e d i ct the t y pe of d e c o m p o s i t i on p r o d u ct that could be p r o d u c ed within c e r t a in c l a s s es of c o m p o u n ds and the e a se with w h i ch t h ey a re m e d i a t e d. In a f ew c a s e s, a t h o r o u gh T he l e a st u n d e r s t o od t r a n s f o r m a t i o ns of p e s t i c i d es in s o i ls in w h i ch to study c h e m i c al r e a c t i o n s, a a re t h o se r e a c t i o ns c a t a l y z ed by the p u r e ly c h e m i c al s y s t e ms as c o m p a r ed to the b i o c h e m i c al s y s t e ms m e d i a t ed by s o il m i c- r o o r g a n i s m s. The m a j or d i f f i c u l ty in d i s t i n g u i s h i ng c h e m i c al f r om b i o c h e m i c al r e a c t i o ns h as b e en to obtain a s t e r i le s o il s y s t em that h as not u n d e r g o ne e x t e n s i ve p h y s i c al and c h e m i c al d e s t r u c t i on due to a u t o c l a v i ng or o t h er m e t h o ds of s t e r i l i z a- tion. As a c o n s e q u e n ce of the d i f f i c u l ty of obtaining s t e r i le s y s t e ms l a r ge m a j o r i ty of the p e s t i c i de t r a n s f o r m a t i o ns h a ve b e en a s c r i b ed to s o il m i c r o o r g a n i s m s. The p r i n c i p al b i o c h e m i c al r e a c t i o ns a s s o c i a t ed with m i c r o b i al m e t a b o l i sm of p e s t i c i d es d e a l k y l a t i o n, d e h a l o g e n a t i o n, a m i de or e s t er h y d r o l y s i s, o x i- d a t i o n, r e d u c t i o n, a r o m a t ic r i ng h y d r o x y l a t i o n, ring c l e a v a ge and c o n d e n s a te or c o n j u g a te f o r m a t i o n. M a ny of t h e se r e a c t i o n s, the e n z y m e s, the p a t h w a ys and the i n t e r m e d i a te p r o d u c ts v ed in p e s t i c i de m e t a b o l i sm h a ve b e en d e s c r i b ed in d e t a i l. A l t h o u gh m a ny of t h e se r e a c t i o ns h a ve b e en d e m o n s t r a t ed as o c c u r r i ng in s o i l s, m o st of the i n f o r m a t i on h as b e en obtained t h r o u gh p u re c u l t u re i n v e s t i g a t i o n s. intact include i n v o l- M e t h yl b r o m i d e. M e t h yl b r o m i de (CH^Br) is a g as and is quite v o l a t i l e. a c t i v i ty is dependent upon g a s e o us d i f f u s i o n. T he d i f f u s i on r a te It is a p p l i ed as a g as b e n e a th a c o v er and its of g a s es is i n f l u e n c ed by m o l e c u l ar w e i g h t, t e m p e r a t u r e, c o n- t i n u i ty of a ir s p a c e s, p r e s e n ce of c o d i f f u s i ng g a s es and d i s t r i- b u t i on of f u m i g a nt b e t w e en a i r, w a t er and s o l id p h a s es of s o i l. T he l a t t er d i s t r i b u t i on is i n f l u e n c ed by t e m p e r a t u r e, m o i s t u r e, a ir s p a c e, c l ay and o r g a n ic m a t t er ( G o r i n g, 1963). L i t t le is known about m e t h yl b r o m i de d e g r a d a t i on in s o i l. U n d er c o n d i t i o ns of f u m i g a t i o n, m e t h yl b r o m i de a d s o r b ed by w h e at u n d e r w e nt d e c o m p o s i t i on with the f o r m a t i on of i n o r g a n ic b r o m i de ( B r i d g e s, 1955; W i n t e r i n g h am et a l, 1955). S o me f r ee m e t h a n ol w as p r o d u c ed by h y d r o l y s i s. M e t h yl b r o m i de w as f o u nd to be a c t i ve in m e t h y l a t i ng the h i s t i d i ne and l y s i ne of w h e at p r o t e in ( B r i d g e s, 1955; W i n t e r i n g h am et a l, 1955). B. S M D C. Due to its h i gh d e g r ee of v o l a t i l i t y, S M DC is m o st f r e q u e n t ly u s ed as a f u m i g a n t. A l t h o u gh i ts m o st e x t e n s i ve u se is f or c o n t r o l l i ng s o i l - b o r ne plant p a t h o g e n s, it h as a l so b e en u s ed as a h e r b i c i d e, p a r t i c u l a r ly f or k i l l i ng w e ed s e e ds in s o i l. S M DC c h e m i c a l ly d e c o m p o s es in s o il to s e v e r al i n- c l u d i ng m e t h yl i s o t h i o c y a n a t e, w h i ch is the p r i m a ry ( G r a y, 1962; L l o y d, 1962; M u n n e c k e, D o m s ch and E c k e r t, 1962; T u r n er and C o r d e n, 1963) ( T a b le 2). T he c h e m i c al r e a c t i o ns of S M DC and its d e c o m p o s i t i on p r o d u c ts h a ve b e en e x a m i n ed u n d er v a r y i ng c o n d i t i o ns of s o il e n v i r o n m e nt ( T u r n er and C o r d e n, In d i l u te a l k a l i ne (pH 9.5) s o l u t i o n s, S M DC d e c o m p o s ed 1963). to m e t h y l i s o t h i o c y a n a te and e l e m e n t al s u l f u r, and in a c id s o l u- tions, c a r b on d i s u l f i d e, h y d r o g en s u l f i d e, m e t h y l a m i n e, m e t h yl i s o t h i o c y a n a te and N , N - d i m e t h y l t h i u r am d i s u l f i de w e re found. p r o d u c t s, t o x i c a nt T a b le 2. D e c o m p o s i t i on P r o d u c ts of S M DC S t r u c t u re C h e m i c al N a me D e s i g n a t i on C o m m on N a me or s o d i um N - m e t h y l d i t h i o- S M DC c a r b a m a te m e t h yl i s o c y a n a te M IT T a b le 2. C o n t i n u e d. S t r u c t u re C h e m i c al N a me D e s i g n a t i on C o m m on N a me or m e t h y l a m i ne c a r b on d i s u l f i de h y d r o g en s u l f i de c s2 h2s m e t h yl t h i o u r ea M TU N , N! - d i m e t h y l t h i o u r ea D M TU N , N' - d i m e t h y l t h i u r am D M TM m o no s u l f i de N , N! - d i m e t h y l t h i u r am d m td d i s u l f i de M o st of t h e se p r o d u c ts w i ll r e a ct w i th one a n o t h er f o r m i ng a d d i t i o n al p r o d u c t s. M e t h y l a m i ne and c a r b on d i s u l f i de r e a c t, f o r m i ng m e t h yl i s o t h i o c y a n a te w h i ch in t u rn c an r e a ct w i th S M D C, y i e l d i ng N , N - d i m e t h y l t h i u r am d i s u l f i d e, and w i th m e t h y l a m i ne or H 2 S, f o r m i ng N , N - d i m e t h y l t h i o u r e a. S M DC as a s o il f u m i g a nt is d e p e n d e nt on i ts c o n v e r s i on to m e t h y l- i s o t h i o c y a n a te ( T u r n er and C o r d e n, 1963), p r o d u c t i on of J N , N - d i- S i n ce the e f f e c t i v e n e ss of m e t h y l t h i o u r ea and N, N - d i m e t h y l t h i u r am d i s u l f i de r e d u c es e f f e c t i v e n e s s. T h e se r e l a t i v e ly n o n v o l a t i le d e c o m p o s i t i on p r o d- u c ts m ay r e p r e s e nt a p o t e n t i al h a z a rd f or c o n t a m i n a t i on of s o i l, w a t er and p l a n ts w i th u n d e s i r a b le r e s i d u es ( K a u f m a n, 1967). A l t h o u gh o t h er p o t e n t i al p r o d u c ts of S M DC d e c o m p o s i t i o n - - e . g ., C S2 and H 2 S - - a re a l so t o x ic c o m p o u n d s, t h e ir high d e g r ee of v o l a t i l i ty would tend to p r e c l u de t h e ir a c c u m u l a t i on in s o i l. its C. D M T T. D M TT b e h a v i or in s o il is quite s i m i l ar to that is a c t u a l ly i ts d e g- of S M D C. T he p r i n c i p al t o x i c a nt of D M TT r a d a t i on p r o d u c t, m e t h yl i s o t h i o c y a n a te ( F i g u re 2). A c t i v a t i on or d e g r a d a t i on of D M TT in s o il is dependent on m o i s t u re and is a f u n c t i on of t i me and t e m p e r a t u re ( T o r g e s o n, Y o d en and John- son, 1957). M e t h yl i s o t h i o c y a n a te r e l e a se o c c u rs as a f i r st o r d er r e a c t i on and i n c r e a s es w i th s o il pH o v er the r a n ge of 2.3 to 6.5, but d e c r e a s es up to v a l u es of pH 7.7 ( M u n n e c k e, 1963). It d e c r e a s ed with i n c r e a s ed c l ay or peat content, and w as not d e p e n d e nt upon s o il m i c r o o r g a n i s m s. Figure 2. Degradation pathway of DMTT. F o r m a l d e h y de and m e t h y l a m i no m e t h y l d i t h i o c a r b a m a te a re the f i r st d e g r a d a t i on p r o d u c t s. M e t h y l a m i no m e t h y l d i t h i o c a r b a- m a te f u r t h er d e g r a d es to m e t h y l a m i n e, h y d r o g en s u l f i de and m e t h y l i s o t h i o c y a n a t e. As with S M DC d e g r a d a t i on p r o d u c t s, m a ny of the D M TT p r o d u c ts r e a ct with one a n o t h er and f o rm a d d i t i o n al p r o d u c t s. M e t h y l a m i ne and h y d r o g en s u l f i de r e a ct w i th f o r m a l d e h y de and f o rm m e t h y l a m i no m e t h a n o l, d i m e t h yl - a m i no m e t h a n e, and 1 , 3 , 5 - t r i t h i o c y c l o h e x a ne w h i ch e v e n t u a l ly d e g r a d es to C O 2, NH3, SO2 and H2O. M e t h yl i s o t h i o c y a n a te w i ll a l so r e a ct with w a t er and f o rm C O 2, H2S and m e t h y l a m i ne ( T o r- g e s o n, Y o d en and Johnson, 1957). M e t h yl i s o t h i o c y a n a te a l so r e a c ts with a m m o n i a, a m i n es or s u l f h y d r y ls ( M u n n e c k e, 1963; M u n n e c ke and M a r t i n, 1964; T o r g e s o n, Y o d en and Johnson, 1957). D. D a l a p o n. D a l a p on is f r e q u e n t ly r e c o m m e n d ed f or c o n- l o ss of d a l a p on by v o l a t i l i ty h as a l so b e en r e- t r o l l i ng spot i n f e s t a t i o ns of w e ed g r a s s es (Anon, 1968a). A l t h o u gh it is r e a d i ly s u s c e p t i b le to b i o d é g r a d a t i on by s o il m i c r o o r g a n i s m s, c o r d e d. K u t s c h i n s ki (1964) r e p o r t ed high dalapon l o s s es at h i gh t e m p e r a t u r es w h en d a l a p on w as a p p l i ed to the s o il as an a c i d. D ay (1961) and D a y, J o r d an and R u s s e ll (1963) s u g g e st a s u f f i c i e n t ly r a p id l o ss to e l i m i n a te s i g n i f i c a nt s o il r e s i d u es in t h e ir s t u d i es with s o me e s t e rs of dalapon. F oy (I960) o b s e r v ed that the d a l a p on a c id v o l a t i l i z ed r a p i d ly f r om an a l u m i n um s u r- f a ce at r o om t e m p e r a t u r e, w h e r e as n e g l i g i b le a m o u n ts of the s o d i um s a lt f o rm d i s a p p e a r ed in 64 h o u rs u n d er the s a me c o n- d i t i o n s. s o il would depend on the c h e m i c al f o rm and the p r e s e n ce and m a g n i t u de of p h y s i c al i n t e r a c t i o ns b e t w e en the m o l e c u l es and s o il p a r t i c l e s. S i n ce t h e re is l i t t le i n t e r a c t i on of d a l a p on with s o il p a r t i c l es ( K e a r n ey et a l, 1965), v o l a t i l i ty at any g i v en t e m- p e r a t u re would p r i m a r i ly be a f u n c t i on of the c h e m i c al f o rm of the m o l e c u le and a ir m o v e m e n t. It would s e em l i k e ly that the v o l a t i l i ty of d a l a p on f r om D a l a p on d e g r a d a t i on by s o il m i c r o o r g a n i s ms is a c c o m p a n- i ed by c h l o r i de ion l i b e r a t i on ( K a u f m a n, 1964). T he d e h a l o g e n- ation of d a l a p on w as d e m o n s t r a t ed with e x t r a c ts of an A r t h r o- b a c t er spp. i s o l a t ed f r om s o il ( K e a r n e y, K a u f m an and B e a l l, 1 9 6 4 a; K e a r n e y, K a u f m an and B e a l l, 1964b). T he e n z y me c a t- a l y z ed the c o n v e r s i on of d a l a p on to p y r u v ic a c i d. T h is r e a c- tion p r e s u m a b ly p r o c e e ds by the i n t e r m e d i a te f o r m a t i on of 2- c h l o r o - 2 - h y d r o x y p r o p i o n a te w h i ch would s p o n t a n e o u s ly y i e ld t he k e to a c i d, p y r u v a te ( F i g u re 3). F u r t h er m e t a b o l i sm i n v o l- v ed the f o r m a t i on of a l a n i n e, C O 2, and p r e s u m a b ly K r eb c y c le i n t e r m e d i a t es ( K e a r n e y, 1966). DALAPON PYRUVATE Figure 3. Enzymatic degradation of dalapon. E. P h e n o x y a l k a n o a t e s. T he p h e n o x y a l k a n o ic a c i ds c o n s t i- tute the l a r g e st and m o st c o m m on c l a ss of h e r b i c i d es u s ed f or c o n t r ol of t u r f g r a ss w e e d s. P h e n o x y a l k a n o a te h e r b i c i d es m o st c o m m o n ly u s ed i n c l u de 2 , 4 - D, 2 , 4 - D P, 2 , 4 , 5 - T, M C PA and s i l- v e x. T he p h e n o x y a l k a n o a t es a re a l so p e r h a ps the m o st i n t e n s e ly s t u d i ed g r o up of p e s t i c i d e s. T he advent of the d i o x in c o n t r o v e r sy h as u n d o u b t e d ly added a d d i t i o n al i m p e t us to the p h e n o x y a l k a n o a te i n ve s t i g a t i o n s. N e a r ly a ll of the p h e n o x y a l k a n o a t es a re m e t a b o l i z ed to s o me e x t e nt by s o il m i c r o o r g a n i s m s. F i ve m e t a b o l ic s t e ps h a ve b e en e s t a b l i s h ed as g e n e r al p r o c e s s es i n v o l v ed in the m e t a b o l i sm of p h e n o x y a l k a n o a t es ( K e a r n e y, K a u f m an and A l e x a n d e r, 1967) ( F i g- u re 4). T h e se r e a c t i o ns i n c l u d e: (1) c o n v e r s i on of n o n f a t t y - a c id s i de c h a i ns to the c o r r e s p o n d i ng f a t ty a c i d s; (2) J3-oxidation of c o m p o u n ds with long f a t ty a c id m o i e t i e s, y i e l d i ng p r o d u c ts with s h o r t er a l k a n o ic a c id m o i e t i e s; (3) c l e a v a ge of the e t h er l i n k a ge b e t w e en the side c h a in and the r i n g; (4) r i ng h y d r o x y l a t i o n, and (5) r i ng c l e a v a g e. S e v e r al of t h e se r e a c t i o ns a re known to o c c ur in s o i l. T he e n z y m o l o gy of m o st of t h e se r e a c t i o ns h as a l so b e en c l a r i f i e d. Figure 4. Degradation pathways of phenoxyalkanoates. E s t e rs of p h e n o x y a l k a n o a t es a re k n o wn to be c o n v e r t ed to t h e ir c o r r e s p o n d i ng p h e n o x y a l k a n o ic a c i ds ( L o o s, 1969). T he h e r b i c i d a l ly i n a c t i ve m o l e c u le s e s o ne (2- 2 , 4 - d i c h l o r o p h e n o xy e t h yl s o d i um s u l f a t e) is a c t i v a t ed m i c r o b i o l o g i c a l ly in m o i st s o il ( L o o s, 1969; V l i t o s, 1952; V l i t o s, 1953). S e s o ne is f i r st c o n v e r t ed to the 2 , 4 - d i c h l o r o p h e n o x y e t h a n ol and s u b s e q u e n t ly to 2 , 4 -D ( V l i t o s, 1952; V l i t o s, 1953). A s i m i l ar r e a c t i on o c c u rs w i th the p h o s p h i te h e r b i c i de 2 , 4 - D EP ( t r is 2 - ( 2 , 4 - d i c h l o r o p h e- n o x y ) e t h yl p h o s p h i t e ). B - O x i d a t i on is k n o wn to o c c ur with p h e n o x y a l k a n o ic a c i ds h a v i ng m o re than two c a r b on a t o ms in the f a t ty a c id side c h a in ( L o o s, 1969). W h e t h er or not t h is p h e n o m e n on w o u ld o c c ur w i th the t wo 2 - p r o p i o n a te s u b s t i t u t ed c o m p o u n ds s i l v ex and 2 , 4 - DP is not k n o w n. T he 2 - p r o p i o n a te s u b s t i t u t e nt c o u ld be c o n s i d e r ed a m e t h yl s u b s t i t u t ed a c e t a te g r o u p. T he i n t r o d u c t i on of m e t h yl s u b s t i t u t e n ts to the a l i p h a t ic a c id g r o up of l o n g - c h a in p h e n o x y- a l k a n o a t es c o n s i d e r a b ly r e t a r ds the J3- o x i d a t i on of t h e se c o m- p o u n ds by s o me m i c r o o r g a n i s ms ( W e b l e y, Duff and F a r m e r, 1959). T h is c o u ld e x p l a in the g e n e r a l ly g r e a t er p e r i od of p e r s i s- t e n ce of s i l v ex and 2 , 4 - DP than t h e ir c o r r e s p o n d i ng a c e t a te 2 , 4 , 5 -T and 2 , 4 - D, r e s p e c t i v e l y. f o r ms C l e a v a ge of the ether l i n k a ge has b e en e x t e n s i v e ly i n v e s- t i g a t ed ( L o o s, 1969). G e n e r a l l y, the a r o m a t ic m o i e ty is r e- l e a s ed as the c o r r e s p o n d i ng phenol in s o i l s, i s o l a t ed b a c t e r- i al c u l t u r es and t h e ir e n z y me s y s t e ms ( K e a r n e y, K a u f m an and A l e x a n d e r, 19 67; L o o s, 19 69). T he i n v e s t i g a t i o ns of Helling, B o l l ag and D a w s on ( 1968) with 1 ^ O - p h e n o x y a c e t a te d e m o n- s t r a t ed that c l e a v a ge o c c u rs b e t w e en the a l i p h a t ic side chain and the ether o x y g en a t o m. R e s t i ng c e l ls and c e l l - f r ee e x- t r a c ts of a s o i l - i s o l a t ed A r t h r o b a c t er sp. q u a n t i t a t i v e ly m e- t a b o l i z ed p h e n o x y -1 ^ o - a c e t ic a c id to p h e n o l- 1 8 o. H y d r o x y l a t i on is a l so a c o m m on r e a c t i on with s o il m i c r o- o r g a n i s ms m e t a b o l i z i ng p e s t i c i d e s. S e v e r al s o il m i c r o o r g a n- i s ms a re a c t i ve in the h y d r o x y l a t i on of 2 , 4 -D and M C PA ( B y r de and W o o d c o c k, 1957). M C PA is m e t a b o l i z ed to 4 - c h l o r o - 2- m e t h y l - 5 - h y d r o x y p h e n o x y a c e t ic a c id ( F a u l k n er and W o o d c o c k, 1965). 2 , 4 -D is a l so h y d r o x y l a t ed in the 5 - p o s i t i o n. It is a l so h y d r o x y l a t ed in the ortho p o s i t i on coupled with a c h l o r i ne shift to 2, 5 - d i c h l o r o - 4 - h y d r o x y p h e n o x y a c e t ic a c i d. A n o t h er o r g a n- i sm m e t a b o l i z es M C PA to s e v e r al p r o d u c t s, including one b e- l i e v ed to be the 6 - h y d r o x y - M C PA (Gaunt and E v a n s, 1961). T he s t e ps i n v o l v ed in ring c l e a v a ge of phenoxyalkanoate h e r b i c i d es h a ve b e en e l u c i d a t ed ( L o o s, 1969; M e n z i e s, 1969). T he c a t e c h o ls p r o d u c ed f r om 2 , 4 -D and M C PA a re c l e a v ed and y i e ld the c o r r e s p o n d i ng c h l o r o m u c o n ic a c i d s. T h e se p r e- s u m a b ly a re a t t a c k ed by r e a c t i o ns involving a dehalogenation and the f o r m a t i on of s i m p le o r g a n ic a c i ds that s e r ve as sub- s t r a t es f or d i v e r se g r o u ps of s o il m i c r o o r g a n i s m s. S i m i l ar m e c h a n i s ms a re b e l i e v ed to function in the m e t a b o l i sm of other s i m i l ar p e s t i c i d es having the b a s ic a r o m a t ic s t r u c t u r e. E x t e n s i ve i n v e s t i g a t i o ns have been conducted to d e t e r m i ne the e f f e ct of m o l e c u l ar s t r u c t u re on the b r e a k d o wn of p h e n o x y- a l k o n a te h e r b i c i d es ( L o o s, 19 69). T he t y p e, p l a ce and n u m b er of substitutents a re a ll known to a f f e ct the r e c a l c i t r a n ce of phenoxy compounds. substitutents on the ring a re s l o w ly d e g r a d e d. Substitutions in p a ra p o s i t i on l a r g e ly o v e r c a me the d e a c t i v a t i ng e f f e ct of other substitutents. M e t h yl substitutents i n c r e a s ed r e c a l c i t- In g e n e r a l, phenoxy compounds with m e ta r a n ee in c o m p a r i s on to h a l o g en s u b s t i t u e n t s. M e t h yl s u b s t i t u- t i on of the s i de c h a in a l so i n c r e a s ed m o l e c u l ar r e c a l c i t r a n ce ( W e b l e y, Duff and F a r m e r, 1959). T h e se v a r i o us c h a r a c t e r i s- t i cs h e lp e x p l a in w hy s o me p h e n o x y a l k a n o a te h e r b i c i d es a re m o re p e r s i s t e nt than o t h e r s. T he u se of t h is g r o up of h e r b i c i d es h as b e en s e v e r ly c r i t- i c i z e d, b a s ed on a r e c e n t ly c o m p l e t ed t e r a t o g e n i c i ty study of 2 , 4 , 5 - T. E x p e r i m e n t al s a m p l es of 2 , 4 , 5 -T w e re r e p o r t ed to p r o d u ce c l e ft p a l a t e, p o l y c y s t ic k i d n e ys and f e t i c i d al e f f e c ts in c e r t a in m i c e. T he d e t e c t i on of t o x ic i m p u r i t i es known to be t e r a t o g e n ic in 2 , 4 , 5 -T h as m a de the s i t u a t i on f ar m o re c o m p l ex than o r i g i n a l ly s u s p e c t e d. One i m p u r i ty h as b e en i d e n t i f i ed as 2 , 3 , 7 , 8 - t e t r a c h l o r o d i b e n z o - p - d i o x in ( T C D D ). T h is compound a r i s es d u r i ng the i n i t i al h y d r o l y s is of t e t r a c h l o r o b e n z e ne to 2 , 4 , 5 - t r i c h l o r o p h e n o l. T he p h e n ol s u b s e q u e n t ly r e a c ts with c h l o r o a c e t ic a c id to f o rm 2 , 4 , 5 - T. P r e v i o u s l y, the h e x a c h l o r- o d i b e n z o - £ - d i o x in w as i m p l i c a t ed in the c h i c k e d e ma but l a t er the t e t r a c h l o ro i s o m er w as shown to be e q u a l ly t o x ic to c h i c ks (Higginbothan et a l, 1968). W h e t h er 2 , 4 , 5 -T or T C DD is the t e r a t o g en is not c l e ar at t h is t i m e. f a c t o r, Its a d s o r p t i on to high o r g a n ic m a t t er s o i ls It F. D i c a m b a. D i c a m ba is quite m o b i le in m o st s o i l s. m o v es c l o se behind the f o r w a rd p e n e t r a t i on f r o nt of w a t er in both s u r f a ce ( F r i e s e n, 1965) and s u b i r r i g a t ed ( H a r r i s, 1964) s o il c o l u m n s. is g r e a t er than f or c l ay or s a n dy s o i l s, and a d s o r p t i on to c l a ys is g r e a t e st onto k a o l i n i te c l a ys ( B u r n s i de and L a v y, 1966). A l t h o u gh d i c a m ba h as r e l a t i v e ly l ow a d s o r p t i on p o t e n t i a l, v o l a t i l i z a t i on is r e d u c ed by s o il c o n t a c t. At e q u i v a l e nt t e m p e r- a t u r es and r e l a t i ve h u m i d i t i e s, n e a r ly half of the r a d i o a c t i v i ty of l ^ C - d i c a m ba w as l o st f r om p l a n c h e ts d u r i ng an 1 1 - w e ek p e r i o d, w h e r e as w as n e g l i g i b le o v er an 8 - w e ek p e r i o d. l o ss by v o l a t i l i z a t i on f r om a s i l ty i ts c l ay l o am D e g r a d a t i on of d i c a m ba o c c u rs m o re r a p i d ly in a c id (pH S.3) than in a l k a l i ne (pH 7.5) s o i ls ( C o r b in and U p c h u r c h, 1967) h i gh in o r g a n ic m a t t e r. S o il m i c r o o r g a n i s ms a re a c t i ve in d e- g r a d i ng d i c a m ba ( W u r z er and C o r b i n, 1968), v ia the d e c a r b o x y l a- t i on m e c h a n i sm to 2 , 5 - d i c h l o r o a n i s o le ( M e n z i e s, 1969) ( F i g u re 5). S u b s e q u e nt s o il d e g r a d a t i on p r o d u c ts h a ve not b e en r e p o r t e d. L i b e r a t i on of c h l o r i de ion f r om d i c a m ba in s o il w as not d e t e c t ed ( S h e e ts and K a u f m a n, 19 65). A l t e r n a t i on of the m e t h o xy s u b- stituent h as b e en s u g g e s t ed but has not b e en s u b s t a n t i a t ed ( S w a n- son, 19 69). F i g u re 5. Degradation of dicamba. D e g r a d a t i on p r o d u c ts o b s e r v ed in plants i n c l u de 5 - h y d r o x y- 2 - m e t h o x y - 3 , 6 - d i c h l o r o b e n z o ic a c i d, 3 , 6 - d i c h l o r o b e n z o ic a c i d, 3 , 6 - d i c h l o r o s a l i c y l ic a c id and 3 , 6 - d i c h l i r o g e n t i s ic a c i d, in a d d i- t i on to one or m o re c o n j u g a te f o r ms ( B r o a d h u r s t, M o n t g o m e ry and F r e e d, 1966; S w a n s o n, 1969). H y d r o l y s is p r o d u c ts of the c o n- j u g a te f o r ms i n c l u de intact d i c a m b a, 5 - h y d r o x y - 2 - m e t h o x y - 3 , 6- d i c h l o r o b e n z o ic a c id and 3 , 6 - d i c h l o r o s a l i c y l ic a c i d. F o r m a t i on of t h e se h y d r o l y s is p r o d u c ts s u g g e s ts c o n j u g a t i on t h r o u gh the c a r b o x y l, m e t h o xy and a h y d r o xy s u b s t i t u e n t. T he f a te of t h e se m a t e r i a ls in our e n v i r o n m e nt is unknown. G. B r o m o x y n i l. B r o m o x y n il and i o x y n il ( 3, 5 - d i i o d o - 4- h y d r o x y b e n z o n i t r i l e) h a ve b e en i n t r o d u c ed r e c e n t ly as h e r b i c i d e s. T h ey w e re r e p o r t ed in 1963 ( C a r p e n t er and H e y w o o d, 1963; Wain, 1963) as p o t e n t i al p o s t e m e r g e n ce h e r b i c i d e s. B r o m o x y n il f or u se in c o n t r o l l i ng c h i c k w e ed ( S t e l l a r ia spp.) w as o b s e r v ed on the s h e lf of a l o c al e m p o r i u m. M o re i n f o r m a t i on is a v a i l a b le on the d e g r a d a t i on of i o x y n il than b r o m o x y n i l. H o w e v e r, t h e ir c l o se s i m i l a r i ty in s t r u c t u r es s u g g e s ts a n a l o g o us m o d es of d e g r a d a t i o n. P h o t o l y s is of the 3, 5 - d i h a l o g e n o - 4 - h y d r o x y b e n z o n i t r i l es m ay be a f a c t or in t h e ir h e r b i c i d al a c t i on as the h e r b i c i d al a c t i on of i o x y n il and b r o m o x y n il has b e en shown to be m o re enhanced in light than in d a rk ( U g o c h u k wu and Wain, 19 65). I r r a d i a t i on with u l t r a v i o l et light f or 20 h o u rs in b e n z e ne c o n v e r t ed i o x y n il to 3 , 5- d i p h e n y l - 4 - h y d r o x y - b e n z o n i t r i l e, with the p o s s i b le i n v o l v e m e nt of f r ee r a d i c a l s. M o re than 7 8 p er cent of the i o x y n il in s o l u t i on w as a d- s o r b ed by the s o il w h en 100 ml of a 1 0 0 0 - p pm s o l u t i on w as s h a k en with 50 g of an a c id s o il (Jones and Hatch, 1937). A l m o st 90 p er cent w as r e m o v ed f r om solution w h en l i m ed p e at w as u s e d. L i me a p p a r e n t ly p r e c i p i t a t es the h e r b i c i de as the r e l a t i v e- ly i n s o l u b le f r ee p h e n o l, r a t h er than r e m o v i ng it by a d s o r p t i on to s o il c o m p o n e n t s. N e a r ly c o m p l e te d e g r a d a t i on w as a c h i e v ed in 19 d a ys in a n o n s t e r i le s o i l, w h e r e as no d e g r a d a t i on w as d e t e c t- a b le in a s t e r i le s o i l. It w as p r o p o s ed that the m i c r o b i al d e g r a- d a t i on of i o x y n il in the s o il p r o d u c es the c o r r e s p o n d i ng a m i de and then the a c id ( F i g u re 6), with d e h a l o g e n a t i on a l so p o s s i b le ( J o n es and H a t c h, 1937). S i m i l ar m e c h a n i sm could be e x p e c t ed to o c c ur with b r o m o x y n i l. Figure 6. Degradation pathway of bromoxynil. H. D C P A. D C PA is a b e n z o ic a c id d e r i v a t i ve w h i ch h as g i v en e x c e l l e nt c o n t r ol of c r a b g r a ss w h en a p p l i ed in the e a r ly s p r i ng b e f o re c r a b g r a ss h as g e r m i n a t ed (Anon, 1968b). V e ry l i t t le i n f o r m a t i o n . is a v a i l a b le about its l a b i l i ty in o ur e n v i r o n- m e n t. C r o s by and L.. M i n g - yu (1969) p r e d i c t ed that t i on of D C PA at w a ve l e n g t hs l o n g er than 290 mu w o u ld p r o d u ce o n ly 2 , 3 , 5 , 6 - t e t r a c h l o r o t e r e p h t h a l ic a c id ( F i g u re 7). T he m o n- o m e t h yl and f r ee d i c a r b o x yl a n a l o g u es h a ve b e en t e n t a t i v e ly i r r a d i a- i d e n t i f i ed a f t er a p p l i c a t i on of D C PA to s o il ( G e r s h on and M c C l u r e, 1966; S k i n n e r, S t a l l a rd and P r i d d l e, 1964). T he m o n- o e t h yl d e r i v a t i ve w as found to u n d e r go d e c a r b o x y l a t i on u n d er the c o n d i t i o ns of g as c h r o m a t o g r a p h y, a c c o r d i ng to S k i n n e r, S t a l l a rd and P r i d d le (1964). F u r t h er d e g r a d a t i on in s o il of the d i c a r b o x yl p r o d u ct 2 , 3 , 5 , 6 - t e t r a c h l o r o p h t h a l ic a c id would p r o- b a b ly i n v o l ve d e c a r b o x y l a t i o n. DCPA F i g u re 7. Degradation pathway of DCPA. I. B e n e f i n. D i n i t r o a n i l i n es h a ve b e en u s ed as d ye i n t e r- m e d i a t es f or s e v e r al d e c a d e s. B o th f u n g i c i d al ( C l a rk and H a m s, 1953) and h e r b i c i d al a c t i v i ty (National R e s e a r ch C o u n c i l, 1955) h a ve b e en d e s c r i b e d. T h e ir u se in t u r f g r a ss a p p l i c a t i on is f or c r a b g r a ss c o n t r o l. B o th a e r o b ic and a n a e r o b ic d e g r a d a t i on p a t h- w a ys h a ve b e en p o s t u l a t ed f or b e n e f in ( P r o b st and T e p e, 1969). E v i d e n ce s u p p o r t i ng the p o s t u l a t ed p a t h w a ys e x i s ts in p o s i t i ve i d e n t i f i c a t i on of c e r t a in of the p r o p o s ed i n t e r m e d i a t es as w e ll as the e s t a b l i s h m e nt of s i m i l ar p a t h w a ys f or the b e n e f in a n a l o g ue t r i f l u r a l in ( a , a , a - t r i f l u o r o - 2 , 6 - d i n i t r o - N , N - d i p r o p y l - p - t o l u i- dine) ( F i g u re 8). CF3 B E N E F IN D E G R A D A T I ON P R O D U C TS ALKYL GROUPS /" R3 NITRO GROUP POSITIONS 2 6 / N 1 C4H9 C4H9 H C4H9 H C4H9 H C4H9 H OH C4H9 C F3 «3 C F3 C F3 C F3 C F3 CF3 C F3 C F3 cf3 C F3 NO 2 NO 2 NO 2 NO 2 NO 2 NO2 NO 2 NH 2 N H2 NO 2 NH 2 NO2 NO 2 NO2 NH2 NO2 NH2 NH2 NH 2 NH2 NO2 NH 2 «1 \ C2H5 H C2H5 C2H5 H H H H H OH C2H5 Figure 8. Degradation products of b e n e f i n. D e a l k y l a t i on f o l l o w ed by p r o g r e s s i ve r e d u c t i on of the n i t ro g r o u ps a p p e a rs to be the m a j or p a t h w ay f or a e r o b ic d e g r a d a t i on ( P r o b st and T e p e, 1969). T he i n i t i al d e a l k y l a t i on s t ep o c c u rs both in s o il and p h o t o c h e m i s t r y. T he i n i t i al d e a l k y l a t ed c o m- pound is a p p a r e n t ly the i n t e r m e d i a te in d u al p a t h w a ys of d e g r a- d a t i o n. One p a t h w ay c o n v e r ts the i n i t i al d e a l k y l a t ed m e t a b o l i te j > ^ - t r i f l u o r o - 5 - n i t r o - N - b u t y l t o l u e n e - 3 , 4 - d i a m i ne by r e d u c- t i on of one n i t ro g r o up p r i or to f u r t h er d e a l k y l a t i o n. T he a l t e r- n a te p a t h w ay i n v o l v es f u r t h er d e a l k y l a t i on and f o r m a t i on of a.,- j a , _ a - t r i f l u o r o - 2 , 6 - d i n i t r o - p - t o l u i d i n e, f o l l o w ed by s u b s e q u e nt s e q u e n t i al r e d u c t i on of the n i t ro g r o u ps to a m i n e s. An addition- al p r o d u ct i s o l a t ed f r om b e n e f in t r e a t ed s o i ls w h i ch h as not b e en r e p o r t ed f or o t h er d i n i t r o - a n i l i ne h e r b i c i d es w as a , a , a - t r i f l u o r o- 2 , 6 - d i n i t r o - j D - c r e s o l. P o l ar p r o d u c ts a re f o r m ed during the d e g- r a d a t i on of b e n e f in and p r o b a b ly a r i se t h r o u gh the f o r m a t i on of a r o m a t ic a m i n e s. A l t h o u gh c e r t a in of the p r o d u c ts o b s e r v ed d u r i ng a n a e r o b ic d e g r a d a t i on a re the s a me as t h o se o b s e r v ed u n d er a e r o b ic d e g- r a d a t i o n, t h e ir o r d er of a p p e a r a n ce is d i f f e r e n t. R e d u c t i on of the n i t ro g r o u ps f o l l o w ed by d e a l k y l a t i on a p p e a rs to be the m a j or a n a e r o b ic d e g r a d a t i on p a t h w a y. T he f o r m a t i on of p o l ar p r o d u c ts a l so is c h a r a c t e r i s t ic of the a n a e r o b ic d e g r a d a t i ve p a t h w a y. T he k ey r e a c t i on a f f e c t i ng the r a te of a n a e r o b ic d e g r a d a t i on of d i n i t r o- a n i l i ne h e r b i c i d es is the f o r m a t i on of the f i r st r e d u c t i ve p r o d u c ts w h i ch s e r ve as the i n t e r m e d i a t es in the f o r m a t i on of e x t r a c t a b le p o l ar p r o d u c ts and n o n e x t r a c t a b le p r o d u c ts ( P r o b st and T e p e, 1969). P h o t o d e c o m p o s i t i on and v o l a t i l i ty a re a l so known to a f f e ct I m p r o v ed h e r b i c i d al a c t i v i ty of the d i n i t r o a n i l i ne c o m p o u n d s. t r i f l u r a l in by s o il i n c o r p o r a t i on w h en c o m p a r ed to s u r f a ce a p p l i- c a t i on ( P i e c z a r k a, W r i g ht and A l d e r, 1962) s u g g e s ts p o s s i b le l o ss by e i t h er v o l a t i l i z a t i on or p h o t o d e c o m p o s i t i o n. T he v a p or p r e s . s u re of t r i f l u r a l in (1.99 x 10-4 mm Hg at 29.5°) s u g g e s ts that v o l a t i l i ty could be a f a c t or u n d er s o me f i e ld conditions ( P r o b st and T e p e, 1969). P h o t o c h e m i c al d e c o m p o s i t i on is c h a r- a c t e r i s t ic of s u b s t i t u t ed a r o m a t ic c o m p o u n ds ( C r o s by and M i n g- y u, 1969; S c h e i n b a u m, 1964). T he p h o t o d e c o m p o s i t i on s e q u e n ce of t r i f l u r a l in i n v o l v ed d e a l k y l a t i o n. T he c h e m i c al s t r u c t u re s i m i l a r i ty of t r i f l u r a l in and b e n e f in and b e n e f i ns i n s t a b i l i ty to l i g ht s u g g e s ts a s i m i l ar p a t h w ay of d e c o m p o s i t i on ( P r o b st and T e p e, 1969). J. T e r b u t o l. T e r b u t ol is a r e c e nt n e w c o m er to the f i e ld of c a r b a m a te h e r b i c i d e s. r e p r e s e n ts a n ew c l a ss of c a r b a m a te h e r b i c i d e s. T e r b u t ol h as found s o me u s a ge as a p r e - e m e r g e n ce c r a b g r a ss c o n t r o l. It is a m e t h y l c a r b a m a te and, as s u c h, i n s e c t i c i d es ( K a u f m a n, 1967). S p e n c er A l t h o u gh v e ry l i t t le is known about the d e g r a d a t i ve m e c h- a n i s ms of m e t h y l c a r b a m a te h e r b i c i d e s, c e r t a in a n a l o g i es h a ve b e en m a de with d e g r a d a t i ve m e c h a n i s ms o b s e r v ed with c e r t a in m e t h y l c a r b a m a te (1965) s u g g e s t ed that m e t h y l c a r b a m a t es w e re s u b j e ct to s e v e r- al p o s s i b le points of m e t a b o l ic a t t a c k, including h y d r o l y s is of the e s t er l i n k a ge and o x i d a t i on of the N - m e t h yl g r o u p, a ring s u b s t i t u e n t, or the r i ng i t s e l f. P r o d u c ts r e s u l t i ng f r om an i n i- t i al a t t a ck at the e s t er l i n k a ge would p r o b a b ly be the enol, c a r- b o n a te ion and a l k y l a m i n e, with m e t h y l i s o c y a n a te as a p o s s i b le i n t e r m e d i a t e. A u g u s t i n s s o n, 1959; C a s i d a, A u g u s t i n s s on and J a n s s o n, I960). M e t h y l c a r b a m ic a c id a l so could be f o r m ed as an i n t e r m e d i a t e, r a t h er than the m e t h y l i s o c y a n a t e. quent p r o d u c ts would be m e t h y l a m i ne and CC>2. ( A e s c h l i m a nn and R e i n e r t, 1 9 3 1; C a s i da and In e i t h er c a s e, the s u b s e- W h e t h er or not the d e g r a d a t i on of t e r b u t ol w o u ld o c c ur by t h is m e c h a n i sm is q u e s t i o n a b le b e c a u se of p o s s i b le s t e r ic i n- h i b i t i on by the p r e s e n ce of the b u l ky t e r t - b u t yl g r o u ps in c l o se p r o x i m i ty to the e s t er l i n k a g e. E v i d e n ce of s u ch a s t e r ic e f- f e ct h as b e en obtained ( K a u f m a n, 1970). We o b s e r v ed a c o m- p e t i t i ve inhibition b e t w e en n u m e r o us m e t h y l c a r b a m a te c o m- pounds and i s o p r o p yl m - c h l o r o c a r b a n i l a te ( c h l o r p r o p h a m) and a c h l o r p r o p h a m - h y d r o l y z i ng e n z y m e. F a i l u re of t e r b u t ol to a ct in a c o m p e t i t i ve f a s h i on w as a t t r i b u t ed to s t e r ic inhibition. B e c a u se of t h is a p p a r e nt s t e r ic inhibition of h y d r o l y s is of the e s t er l i n k a g e, it w as s u g g e s t ed ( K a u f m a n, 1967) that t e r b u t ol m i g ht be m o re p e r s i s t e nt in s o il than o t h er c a r b a m a te h e r b i- c i d e s. K. N e b u r on and Siduron. N e b u r on and s i d u r on a re both p h e n y l u r ea h e r b i c i d e s. N e b u r on c o n t a i ns t wo a l k yl s u b s t i t- u e n t s, an n - b u t yl g r o up and a m e t h yl g r o u p, w h e r e as s i d u r on c o n t a i ns a s i n g le 2 - m e t h y l c y c l o h e x yl substitutent on the a m i ne g r o up of the u r ea l i n k a g e. N u m e r o us p r o c e s s es a re known to a f f e ct the d e g r a d a t i on of p h e n y l u r ea h e r b i c i d es in s o il ( S h e e t s, 1 9 6 4 a ). A l t h o u gh no s y s t e m a t ic s t u d i es h a ve b e en c a r r i ed out, u r ea h e r b i c i d es a p p e ar to be s u f f i c i e n t ly s t a b le u n d er n o r m al t e m p e r a t u re and s o il c o n d i t i o ns to r e s i st h y d r o l y t ic b r e a k d o wn or o x i d a t i on by p u r e ly c h e m i c al m e a ns ( G e i s s b u h l e r, 1969; H i ll et a l, 1955). No u n e q u i v o c al e x a m p l es of the r e d u c t i on of u r ea h e r b i c i de p h y t o t o x i c i ty in the f i e l d, due to the a c t i on of sunlight, h a ve b e en r e p o r t e d. C o n s i d e r a b le c i r c u m s t a n t i al e v i d e n ce d i c a t e s, h o w e v e r, that light r e p r e s e n ts an i m p o r t a nt f a c t or t he a p p l i c a b i l i ty and e n v i r o n m e n t al f a te of t h e se h e r b i c i d es ( A s h t o n, 1 9 6 5; C o m es and T i m m o n s, 1965). A m o ng the m o st c o m m on u r ea h e r b i c i d e s, n e b u r on w as m o re s t a b le to t h an 3 - p h e n y l - 1 , 1 - d i m e t h y l u r ea (fenuron), 3 -(]D-chlorophenyl) - 1 , 1 - d i m e t h y l u r ea ( m o n u r o n ), or 3 - ( 3 , 4 - d i c h l o r o p h e n y l ) - l , l- d i m e t h y l u r ea (diuron) ( J o r d a n, D ay and C l e r x, 1963). i n- in l i g ht P h o t o c h e m i c al p r o d u c ts of m o n u r on in s o l u t i on r e s u l t ed in r e p l a c e m e nt of the a r o m a t ic c h l o r i ne by a h y d r o x yl g r o up and e l i m i n a t i on of d i m e t h y l a m i ne to g i ve 4 - c h l o r o p h e n yl ( C r o s by and M i n g - y u, 1969). P r e s u m a b l y, the c o r r e s p o n d i ng p r o d u c ts w o u ld be f o r m ed d u r i ng p r o t o c h e m i c al d e g r a d a t i on of s i d u r on or n e b u r o n. i s o c y a n a te N - D e a l k y l a t i on is the m a j or d e g r a d a t i on p a t h w ay of u r ea h e r b i c i d es by s o il m i c r o o r g a n i s ms ( G e i s s b u h l e r, 1969). N- D e a l k y l a t i on r e s u l ts in the f o r m a t i on of the c o r r e s p o n d i ng a l c o h o ls and p h e n y l u r e a s. S u b s e q u e nt d e g r a d a t i on p r o d u c ts of the p h e n y l u r e as w o u ld be cc>2, n h 3, and the c o r r e s p o n d i ng a n i l i n e. D e g r a d a t i on of n e b u r on w o u ld r e s u lt in the e v e n t u al f o r m a t i on of 3 , 4 - d i c h l o r o a n i l i n e, C O 2, n h 3, m e t h a n ol and n- b u t a n ol ( F i g u re 9). T he a l c o h o ls w o u ld be r e a d i ly d e g r a d ed by s o il m i c r o o r g a n i s m s. R e c e nt e v i d e n ce h as d e m o n s t r a t ed that the 3 , 4 - d i c h l o r o a n i l i ne m o i e ty is r e c a l c i t r a nt ( B a r t h a, L a n z i- l o t ta and P r a m e r, 1967) to b i o d é g r a d a t i o n. F u r t h e r, it m ay be c o n d e n s ed to 3 , 3f, 4 , 4!- t e t r a c h l o r o a z o b e n z e ne P r a m e r, 1967). M o re r e c e nt e v i d e n c e, h o w e v e r, w o u ld c a te that v e ry l i t t l e, if a n y, a z o b e n z e n es w o u ld be f o r m ed f r om a n i l i n e - b a s ed h e r b i c i d es w h i ch a re d e g r a d ed o n ly v e ry s l o w ly (D. D. K a u f m a n, u n p u b l i s h ed data). ( B a r t ha and i n d i- Figure 9. Degradation pathway of neburon. A s i m i l ar d e g r a d a t i on p a t h w ay could be e x p e c t ed with s i d- u r o n. D e g r a d a t i on p r o d u c ts m i g ht i n c l u de C O 2, NH3, aniline and 2 - m e t h y l c y c l o h e x a n o l. T he p r e s e n ce of the b u l ky 2 - m e t h y- l c y c l o h e x yl g r o up as a s u b s t i t u t e n t, h o w e v e r, m a ny p r e c l u de d e a l k y l a t i on as a m a j or d e g r a d a t i on p a t h w ay f or t h is compound and o t h er d e g r a d a t i ve m e c h a n i s ms m ay be m o re i m p o r t a n t. T he l o ng p e r s i s t e n ce p e r i od of 12 m o n t hs or m o re could i n d i c a te the i n a b i l i ty of s o il m i c r o o r g a n i s ms to r e a d i ly d e g r a de s i d u r o n. L. s - T r i a z i n e s. T he s - t r i a z i n e s, a t r a z i ne and s i m a z i n e, a re a l so u s ed as t u r f g r a ss h e r b i c i d e s. In s o u t h e rn s t a t e s, a t r a z i ne h as b e en u s ed f or p r e - e m e r g e n ce c o n t r ol of c r a b g r a s s, g o o s e- g r a ss and m o st b r o a d l e af w e e ds in e s t a b l i s h ed t u r f. In the P a- c i f ic N o r t h w e s t, g r a ss s e ed p r o d u c e rs h a ve u s ed both a t r a z i ne and s i m a z i ne f or p r o d u c i ng high q u a l i ty s e e d, f r ee f r om w e ed s e ed c o n t a m i n a t i o n. T he s - t r i a z i n es a re g e n e r a l ly r e c o g n i z ed to be a m o ng the m o re p e r s i s t e nt h e r b i c i d e s. R e s i d u al p h y t o t o x i c i ty of s - t r i a- z i n es h as b e en o b s e r v ed f r om 3 to 12 m o n t hs at r a t es of 4 l b/ a c re or b e l ow ( H a r r is et a l, 1968). At r a t es a b o ve 4 l b / a c r e, r e s i d u al p h y t o t o x i c i t i es of the _ s - t r i a z i n es m ay l a st t h an 12 m o n t h s. A l t h o u gh the r e s i d u al p h y t o t o x i c i ty of e i t h er a t r a z i ne or s i m a z i ne h as b e en c i t ed as g r e a t er than the o t h er in i n d i v i d u al p a p e r s, t h e re d o es not a p p e ar to be any d i f f e r e n ce in r e s i d u al p h y t o t o x i c i ty b e t w e en the t wo w h en a ll e v i d e n ce c o n s i d e r ed c o l l e c t i v e ly ( H a r r is et a l, 1968). l o n g er is S i m a z i ne and a t r a z i ne a re d e g r a d ed by both b i o l o g i c al and c h e m i c al m e c h a n i s ms ( F i g u re 10). B i o d é g r a d a t i on of the _ s - t r i a z i n es p r o c e e ds by N - d e a l k y l a t i on ( K a u f m an and K e a r n e y, 1 9 7 0; K a u f m a n, K e a r n ey and S h e e t s, 1965; K e a r n e y, K a u f m an and S h e e t s, 1965). S i m a z i ne m e t a b o l i sm by s o il fungi r e s u l t- ed in the f o r m a t i on of 2 - c h l o r o - 4 - a m i n o - 6 - e t h y l a m i n o - s - t r i a- z i ne ( K a u f m a n, K e a r n ey and S h e e t s, 1965; K e a r n e y, K a u f m an and S h e e t s, 1965), w h e r e as a t r a z i ne w as m e t a b o l i z ed to both 2 - c h l o r o - 4 - a m i n o - 6 - e t h y l a m i n o - _ s - t r i a z i ne and 2 - c h l o r o - 4- a m i n o - 6 - i s o p r o p y l a m i n o - j 3 - t r i a z i ne ( K a u f m an and B l a k e, 1970). S u b s e q u e nt m e t a b o l i sm of 2 - c h l o r o - 4 - e t h y l a m i n o - s - t r i a z i ne r e s u l t ed in f u r t h er d e a l k y l a t i on or d e a m i n a t i on or both, f o l- l o w ed by a d e h a l o g e n a t i on of the m o l e c u le with the e v e n t u al f o r m a t i on of a m m e l i de ( K e a r n e y, K a u f m an and S h e e t s, 1965). Figure 10. Chemical and biochemical degradation pathways of c h l o r o - s - t r i a z i n e s. C h e m i c al d e g r a d a t i on of s i m a z i ne and a t r a z i ne o c c u rs by in s o il ( H a r r i s, 1967); h o w e v e r, d e a l k y- d e h a l o g e n a t i on with the f o r m a t i on of the c o r r e s p o n d i ng 2 - h y d o x y- J 3 - t r i a z i n e s. T h is p r o c e ss a p p e a rs to be the m a j or d e g r a d a t i ve m e c h a n i sm o c c u r r i ng l a t ed p r o d u c ts h a ve b e en i s o l a t ed f r om s o il and i d e n t i f i ed (Obien and G r e e n, 1969). A l t h o u gh the h y d r o x y - j s - t r i a z i n es a re known to be d e g r a d ed m o re r e a d i ly in s o il than the c h l o r o - s u b s t i t u t ed f o r ms ( S k i p p e r, 1970), t h e ir d e g r a d a t i on m e c h a n i sm is not k n o w n. D e a l k y l a t i on and d e a m i n a t i on of the h y d r o xy a t r a z i ne and h y d r o xy s i m a z i ne could e v e n t u a l ly r e s u lt in the s a me end p r o d u c t - - a m m e d l i d e. S u b s e q u e nt d e g r a d a t i on p r o d u c ts h a ve not as y et b e en r e p o r t e d. r i ng l a b e l ed s - t r i a z i n es i n d i c a te the ring c l e a v a ge d o es o c c ur w i th the s u b s e q u e nt e v o l u t i on of I n v e s t i g a t i o ns c o n d u c t ed with l i s h ed d a t a; S k i p p e r, G i l m o ur and F u r t i c k, 1967). T he m e c h- a n i sm by w h i ch r i ng c l e a v a ge o c c u rs r e m a i ns to be v e r i f i e d. M. D M P A. D M PA h as p r o v i d ed good c o n t r ol of c r a b g r a ss (D. D. K a u f m a n; unpub- in the e a r ly s p r i ng b e f o re It is m o d e r a t e ly w h en a p p l i ed at 1 5 to 20 l b s / a c re c r a b g r a ss h as g e r m i n a t ed (Anon, 1968b). s u s c e p t i b le to p h o t o l y s i s, and p e r s i s ts f or 6 to 8 w e e ks in s o il at r e c o m m e n d ed r a t e s. V e ry l i t t le is known about the d e g r a d a- t i on of D M PA in s o i l. S e v e r al s i t es of a t t a ck a re p o s s i b le on the m o l e c u l e. H y d r o l y s is to 2 , 4 - d i c h l o r o p h e n ol and O - m e t h yl i s o p r o p yl p h o s p h o r a m i d o t h i o a te is a p p a r e n t ly the m a j or m o de of d e g r a d a t i o n. A s o il f u n g u s, A s p e r g i l l us c l a v a t u s, d e g r a d ed both D M PA and t r a ce a m o u n ts of 2 , 4 - d i c h l o r o p h e n ol w h i ch a p- p e a r ed in the c u l t u re m e d ia ( F i e l ds and H e m p h i l l, 1966). T he g r o w th of o t h er s o il f u n gi w as s t i m u l a t ed by »O-methyl p r o p yl p h o s p h o r a m i d o t h i o a t e. i s o- N. B e n s u l i d e. B e n s u l i de is a l so u s ed f or the c o n t r ol of c r a b g r a s s, but l a wn g r a s s es cannot be r e s e e d ed f or 6 to 12 m o n t hs f o l l o w i ng a p p l i c a t i o n, depending upon the amount of r a in and s o il t y p e. We know v e ry l i t t le about the m o de of d e g r a d a- t i on of b e n s u l i de in s o i l. It a p p e a rs to be m o re p e r s i s t e nt than m o st o r g a n o p h o s p h a te p e s t i c i d e s. O. P a r a q u a t. P a r a q u at h as b e en u s ed in s o u t h e rn r e g i o ns f or p o s t - e m e r g e n ce c o n t r ol of w i n t er a n n u a ls in d o r m a nt t u r f. It is r e g i s t e r ed f or w e ed c o n t r ol d u r i ng e s t a b l i s h m e nt of g r a ss s e ed c r o ps ( C a l d e r b a n k, 1968; W e ed S c i e n ce S o c i e ty of A m e r i c a, It is 19 67). P a r a q u at a c ts p r i m a r i ly as a c o n t a ct h e r b i c i d e. v e ry r a p i d ly a d s o r b ed by plant f o l i a g e, and is r e s i s t a nt to r e- m o v al by r a i n. V e ry l i t t le is k n o wn about the p e r s i s t e n ce of p a r a q u at in s o i l s. P a r a q u at is unique a m o ng h e r b i c i d es in i ts s o il b e h a v- i or in that it is v e ry r a p i d ly and s t r o n g ly a d s o r b ed on s o il and, h e n c e, c o m p l e t e ly i n a c t i v a t ed by soil. f r om s o il by o r d i n a ry l e a c h i n g, w a s h i ng or s o l v e nt e x t r a c t i o n. R e f l u x i ng with 18 N s u l f u r ic a c id is n e c e s s a ry to r e m o ve p a r- aquat f r om s o il ( C a l d e r b a n k, 1968). M o st s o i ls s u p p o s e d ly h a ve s u f f i c i e nt c a p a c i ty in the top i n ch of s o il alone to bind m a ny hundred t i m es the n o r m al f i e ld r a t es of a p p l i c a t i on of p a r a q u a t. It cannot be r e m o v ed F r ee of the s o i l, l o ss of p a r a q u at c an o c c ur v ia p h o t o c h e m- i c al d e c o m p o s i t i on or m i c r o b i al d e g r a d a t i o n. P h o t o c h e m i c al d e g r a d a t i on of p a r a q u at r e s u l t ed in the f o r m a t i on of t wo m a j or p r o d u c t s, 4 - c a r b o x y - 1 - m e t h y l p y r i d i n i um c h l o r i de and m e t h y l- a m i ne h y d r o c h l o r i de ( S l a c l e, 19 65). C a r b o n yl c o m p o u n ds w e re s u s p e c t ed as t r a n s i t o ry i n t e r m e d i a t e s. T h e se s a me p r o d u c ts w e re shown to r e s u lt f r om p h o t o c h e m i c al d e g r a d a t i on of p a r a- quat on the s u r f a ce of plants in d a y l i g ht ( S l a d e, 19 66). T he u l t- i m a te f a te of t h e se c o m p o u n ds in our e n v i r o n m e nt is not known at p r e s e n t. A w i de v a r i e ty of m i c r o o r g a n i s ms a re c a p a b le of d e g r a d i ng p a r a q u at ( B a l d w i n, B r ay and G e o g h e g a n, 1966; C a l d e r b a n k, 1968). R e d u c t i on of p a r a q u at to c o l o r ed f r ee r a d i c a ls h as b e en o b s e r v ed in f u n g al and b a c t e r i al c u l t u r e s. Only one p r o d u ct h as b e en t e n- t a t i v e ly i d e n t i f i ed as r e s u l t i ng f r om m i c r o b i al d e c o m p o s i t i o n: 4- c a r b o x y - 1 - m e t h yl p y r i d i n i um c h l o r i de ( B o z a r t h, F u n d e r b u rk and C u r l, 1966). O t h er p r o d u c ts r e m a in to be i d e n t i f i e d. P. K O C N. P o t a s s i um c y a n a te ( K O C N) h as b e en u s ed f or p o s t - e m e r g e n ce of c r a b g r a ss as w e ll as being a f u n g i c i d e. d e c o m p o s es r a p i d ly in a q u e o us s y s t e ms to p o t a s s i um c a r b o n a te and a m m o n ia and d o es not a c c u m u l a te in s o il ( T h o m s o n, 19 67). B o th of t h e se d e g r a d a t i on p r o d u c ts could u l t i m a t e ly be of s o me f e r t i l i z er v a l u e. It Q. P M A. T he d e g r a d a t i on of s e v e r al o r g a n o m e r c u r i a ls h as b e en r e p o r t ed ( M e n z i e s, 1969). P MA is d e g r a d ed in s o il and l o st as m e t a l l ic m e r c u ry v a p o rs ( K i m u ra and M i l l e r, 19 64). P MA is d e g r a d ed m o re r a p i d ly in n o n a u t o c l a v ed s o il than in a u t o c l a v ed s o i l, s u g g e s t i ng the r o le of b i o l o g i c al p r o- c e s s e s. E s s e n t i a l ly the s a me p r o d u c t s, h o w e v e r, w e re r e c o v- e r ed f r om both a u t o c l a v ed and n o n a u t o c l a v ed s o i l s. P r e s u m- a b l y, the b i o l o g i c al and c h e m i c al d e g r a d a t i on p a t h w ay would be the s a me ( F i g u re 11). PMA Figure 1 1. Degradation pathway of PMA. B o o er ( 1944) p o s t u l a t ed that o r g a n ic m e r c u ry c o m p o u n ds i n t e r m e d- r e a c t ed by b a se e x c h a n ge with s o il c l a ys to f o rm an i a te compound. In the c a se of P M A, the i n t e r m e d i a t es would be a d i p h e n y l m e r c u ry and a m e r c u ry c l ay compound. T he d i- p h e n y l m e r c u ry compound would a c c u m u l a te in s o i l, w h e r e as m e t a l l ic m e r c u ry would r e s u lt f r om d e g r a d a t i on of the c l ay c o m p l e x. T he m e t a l l ic m e r c u ry would be r e n d e r ed by f o r m a t i on of m e r c u ry s u l f i d e. T h e se r e s u l ts w e re not c o m- p l e t e ly c o n f i r m ed in l a t er s t u d i es by K i m u ra and M i l l er ( 19 64), innocuous w ho found that P MA w as d e g r a d ed in s o il and l o st as the m e t a l- l ic m e r c u ry v a p o r. T h ey r e c o v e r ed 1 4 - 16 p er cent of o r i g i n al P MA a p p l i ed as the m e r c u ry v a p o r. A p p r o x i m a t e ly 60-70 p er c e nt w as r e c o v e r ed as the intact P M A. A l t h o u gh the r e m a i n i ng m e r c u ry r e s i d u es w e re r e c o v e r a b l e, t h ey w e re not c h a r a c t e r- i z e d. R. A r s e n i c a l s. In r e c e nt y e a rs the o r g a n ic a r s e n i c a ls h a ve b e en u s ed to c o n t r ol c e r t a in p e r e n n i al w e e d s. D S M A, M S M A, M A MA and c a c o d y l ic a c id a re i m p o r t a nt e x a m p l es of this c l a ss of c o m p o u n d s. D S M A, M A MA and M S MA a re c o m m o n ly u s ed in t u r f g r a ss f or p o s t - e m e r g e n ce c o n t r ol of c r a b g r a ss (Anon, 1968a). C a c o d y l ic a c id k i l ls a ll g r a s s es and is g e n e r a l ly u s ed o n ly f or sod r e n o v a t i on and spot t r e a t m e n ts (Weed S c i e n ce S o c i- e ty of A m e r i c a, 1967). I n f o r m a t i on on the p e r s i s t e n ce of a r s e n- i c a ls in s o il is e x t r e m e ly m e a g e r. A v a i l a b le i n f o r m a t i on c a t es that a r s e n ic r e s i d u es tend to a c c u m u l a te in s o i l. L e ad and c a l c i um a r s e n a te w e re u s ed f or m a ny y e a rs f or i n s e ct c o n- t r ol in t o b a c c o, cotton, o r c h a r ds and o t h er c r o p s. A r s e n ic r e s- i d u es in the s u r f a ce 8 i n c h es of o r c h a rd s o i ls r a n g ed f r om 23.2 to 580 p pm of A S 2 O3 in 21 s a m p l es c o l l e c t ed in the n o r t h w e st ( J o n es and H a t c h, 1937). In a m o re r e c e nt s u r v ey by W o o l s o n, A x l ey and K e a r n ey ( 1 9 7 1 ), a r a n ge of 0 to 2500 p pm a r s e n i c, w i th an a v e r a ge v a l ue of 165 p p m, w as found in o r c h a rd s o i ls w h i ch w e re f i r st t r e a t ed about 40 y e a rs a go and s o me of w h i ch a re s t i ll u n d er t r e a t m e nt t o d a y. T h e se s a m p l es w e re c o l l e c t ed f r om the s t a t es of W a s h i n g t o n, Idaho, M o n t a n a, N ew Y o r k, O r e g o n, F l o r i d a, Indiana, M a r y l a nd and M a i n e. S u b s e q u e nt c r o ps h a ve o f t en f a i l ed to s u r v i ve on t h e se abandoned o r c h a rd s o i l s. i n d i- S c h w e i z er (1967) h as c a l c u l a t ed that at n o r m al r a t es of a p- p l i c a t i on of D S MA in M i s s i s s i p pi ( e q u i v a l e nt to 6 kg p er h e c t a re p er y e a r ), m o re than 50 y e a rs would e l a p se b e f o re a r s e n ic r e s i- d u es w o u ld r e a ch t o x ic l e v e ls in cotton. In c o n t r a s t, r i ce is v e ry s u s c e p t i b le to D S MA r e s i d u es and p h y t o t o x ic l e v e ls m ay be r e a c h- ed in the t i me r a n ge of 3 to 80 y e a r s, depending on s o il type. M e t a b o l i sm of m o st o r g a n ic h e r b i c i d es l e a ds to the f o r m a- t i on of l e ss t o x ic c o m p o u n d s. M e t a b o l i sm of D S MA (LD5Q 700 to 1000) and M S MA in s o il y i e l ds the i n o r g a n ic a r s e n a te (LD50 40 to 1 0 0 ) - -a c o m p o u nd that is 10 to 25 t i m es m o re t o x ic (Von Endt, 19 68). Both m e t h y l a t i on and d e m e t h y l a t i on r e a c t i o ns m ay o c c ur in the c o u r se of m i c r o b i al m e t a b o l i sm of a r s e n i c a l s. C h a l l e n g er ( 19 51) p o s t u l a t ed that m e t h a n e a r s o n ic a c i d, c a c o d y l ic a c id and t r i m e t h y l a r s i ne r e s u l t ed f r om p r o g r e s s i ve m e t h y l a t i on of a r s e n- i o us a c i d. D e m e t h y l a t i on of D S MA and M S MA r e s u l t ed in the f o r m a t i on of the i n o r g a n ic a r s o n a te ( V on Endt, 19 68). A r s e n ic r e a c t i o ns in s o il a re c o m p l e x. C o n s e q u e n t l y, it would be e r r o n e o us to a s s u me that e q u al a p p l i c a t i o ns to d i f f e r e nt s o il t y p es would y i e ld the s a me d e g r ee of r e s i d u al p h y t o t o x i c i t y. A r s e n ic e x i s ts in f o ur p r i n c i p al f o r ms in s o i l s; i . e ., the w a t er s o l u b l e, c a l c i u m ,, a l u m i n um and i r on a r s e n a t e s. P r e l i m i n a ry e x p e r i m e n ts at B e l t s v i l le a s s e s s i ng the p h y t o t o x i c i ty of e a ch of t h e se f o ur f r a c t i o ns s u g g e st that w a t er s o l u b le and p'ossibly c a l c i um a r s e n a te exhibit p h y t o t o x i c i ty ( W o o l s o n, A x l ey and K e a r n e y, 1971). S e v e r al f a c t o rs g o v e rn the f a te and b e h a v i or of a r s e n ic in l e ss a v a i l a b le f or plant uptake as s o i l. T he a v a i l a b i l i ty of a r s e n ic to p l a n ts is p a r t ly m e d i a t ed by s o il pH. A r s e n ic b e c o m es s o il pH i n c r e a s es with the f o r m a t i on of i n s o l u b le c a l c i um a r s e n- a t e s. S o i ls of high c l ay content with i n c r e a s ed i r on and a l u m i- num c o n c e n t r a t i o ns a re m o re a b le to c o m p l ex a r s e n a te than s o i ls of l i g h t er t e x t u r e. S i n ce a r s e n ic and p h o s p h o r us a re c h e m- i c a l ly s i m i l a r, the a v a i l a b i l i ty of a r s e n ic f or plant uptake is p r o- p o r t i o n al to the p h o s p h o r us content of the s o il ( E v e r e t t, 19 63). T he s u s c e p t i b i l i ty of i n d i v i d u al plant s p e c i es is an f a c t or in a s s e s s i ng a r s e n ic t o x i c i ty in s o i l s. M e t h o ds of i n a c t- i v a t i ng t o x ic a r s e n ic r e s i d u es in s o i ls a re c u r r e n t ly u n d er i n- v e s t i g a t i on at B e l t s v i l le ( W o o l s o n, A x l ey and K e a r n e y, 19 71). i m p o r t a nt S. F o r m u l a t i on e f f e c t s. So f ar we h a ve d i s c u s s ed the p e r- s i s t e n ce and d e g r a d a t i on of t h e se c h e m i c a ls as though t h ey w e re the only p e s t i c i de p r e s e nt in s o i l, or that t h ey w e re a p p l i ed as t e c h n i c al g r a de m a t e r i a l s. T h is is not the c a s e, h o w e v e r, in a c- t u al p r a c t i c e. M o st f r e q u e n t ly p e s t i c i de c h e m i c a ls a re a p p l i ed in c o m b i n a t i on with e i t h er f e r t i l i z e rs or o t h er p e s t i c i d es or both. F u r t h e r, t h ey m ay be a p p l i ed as s i m p le or c o m p l ex e s t e r, or It is w e ll k n o wn that the b e h a v i or p a t t e rn of s a lt f o r m u l a t i o n s. p e s t i c i d es m ay c h a n ge r a d i c a l ly with c h a n g es in f o r m u l a t i o n. S e v e r al of the c o m m o n ly u s ed t u r f g r a ss h e r b i c i d es a re in n u m e r o us s a lt or e s t er f o r m u l a t i o ns ( T a b le 3), a v a i l a b le and a re g e n e r a l ly l i n k ed to the p e s t i c i de m o l e c u le t h r o u gh the c a r b o x yl g r o up of the p e s t i c i d e. As r e p o r t ed e a r l i e r, s o il m i c r o o r g a n i s ms a re c a p a b le of d e g r a d i ng c e r t a in e s t e rs of 2 , 4 -D ( V l i t o s, 1952; V l i t o s, 1953), p r e s u m a b ly s i m p le h y d r o l y s i s. H o w e v e r, s o me e v i d e n ce f or f i c a t i on and s o me type of b e t a - o x i d a t i on h as b e en s u g g e s t ed in c e r t a in p l a n ts (Helling, B o l l ag and D a w s o n, 1968; T r i c h e l l, M o r t on and M e r k l e, 1968). S u b s e q u e nt to h y d r o l y s i s, 2 , 4 -D w o u ld be s u b j e ct to the d e g r a d a t i ve m e c h a n i s ms d e s c r i b ed e a r l i e r. M a n o m e t r ic e v i d e n ce h as b e en obtained that m i c r o- o r g a n i s ms c an o x i d i ze the a l c o h ol m o i e ty of the i s o p r o p yl and b u t yl e s t e rs of 2 , 4 -D ( A ly and F a u s t, 1964). t h r o u gh t r a n s e s t e r i- T a b le 3. C o m m on E s t er and Salt F o r m u l a t i o ns f or T u r f g r a ss H e r b i c i d es E s t er s S a l ts i s o p r o p yl i s o o c t yl 2 - e t h y l h e x yl b u t o x y e t h a n ol p r o p y l e ne g y l c ol d i m e t h y l a m i ne d i e t h a n o l a m i ne t r i e t h y l a m i ne o c t y l a m m o n i um d o d e c y l a m m o n i um N - o l e y l - 1 ,3 - p r o p y l e n e d i a m i ne C o n s i d e r a b le i n f o r m a t i on e x i s ts on the v o l a t i l i ty of e s t e rs of 2 , 4 -D and r e l a t ed c o m p o u n ds ( A d a m s, J a c k s on and B a r n e s- b e r g e r, 1964; B a s k in and W a l k e r, 1953; D a y, Johnson and Dew- l e n, 1959; F l i n t, A l e x a n d er and F u n d e r b u r k, 1963; H i l t o n , J e n- s en and H u l l, 1963; J e n s en and S c h a l l, 1966). E s t e rs of 2 , 4 -D c an be d i v i d ed into two g r o u ps b a s ed on v o l a t i l i t y; the i s o o c t yl (the p r o p y l e ne g l y c ol butly ether) and the b u t o x y e t h a n ol (low v o l a t i le e s t e r s ). T h e se a re about 10 to 20 t i m es l e ss v o l a t i le i s o p r o p yl than the l o w er a l k yl e s t e rs of 2 , 4 - D, w h i ch include the and N - b u t yl e s t er ( F l i n t, A l e x a n d er and F u n d e r b u r k, 1963). U s u a l l y, p h e n o x y a c e t ic e s t e rs that contain f i ve c a r b o ns or l e ss in the a l c o h ol m o i e ty a re c o n s i d e r ed " h i g h ly v o l a t i l e ," w h e r e as t h o se that c o n t a in m o re than f i ve a re " l ow v o l a t i l e" e s t e rs ( B a s- k in and W a l k e r, 1953). A f u r t h er r e f i n e m e nt in the d e f i n i t i on of " h i g h ly v o l a t i l e" c o m es f r om a s o p h i s t i c a t ed a p p r o a ch u s i ng g as l i q u id c h r o m a t o g r a p hy to m e a s u re v a p or p r e s s u re of 24 e s t e rs of 2 , 4 -D and 2 , 4 , 5 -T (Hilton, J a n s en and Hull, 1963). A " h i g h ly v o l a t i l e" e s t er is d e f i n ed as any p h e n o xy h e r b i c i de with a v a p or p r e s s u re g r e a t er than 1 .5 x 1 0 -4 mm Hg at 2 5 ° C. w h e t h er or not t h e se c r i t e r ia c an be a p p l i ed to o t h er p e s t i c i de m u l a t i o n s. It is not known f o r- A l t h o u gh c o n s i d e r a b le i n f o r m a t i on is known about p h y t o- t o x ic i n t e r a c t i o ns of p e s t i c i de c o m b i n a t i o n s, v e ry l i t t le is known about t h e ir i n t e r a c t i o ns w h i ch m ay a f f e ct b e h a v i or in s o i l. We h a ve r e c e n t ly b e en w o r k i ng on the b i o d é g r a d a t i on of p e s t i c i de c o m b i n a t i o ns in s o il and h a ve o b s e r v ed s e v e r al s t r i k i ng e f f e c ts in t e r ms of a l t e r ed p e r s i s t e n ce ( B a r n e tt et a l, 1967; D. D. K a u f- m a n, u n p u b l i s h ed data). F or e x a m p l e, the p e r s i s t e n ce of p h e n y l- c a r b a m a te h e r b i c i de c h l o r p r o p h am ( i s o p r o p yl m - c h l o r o c a r b a n i- late) is i n c r e a s ed in s o il in the p r e s e n ce of s e v e r al m e t h y l c a r- b a m a te i n s e c t i c i d e s. T h is p h e n o m e n on w as e x p l a i n ed by a c o m- p e t i t i ve inhibition of the c h l o r p r o p h a m - h y d r o l y z i ng e n z y me of s o il m i c r o o r g a n i s ms by c e r t a in m e t h y l c a r b a m a t e s. We h a ve a l so o b s e r v ed that the h e r b i c i d e, d i c a m b a, m ay be p a r t i a l ly d e- g r a d ed m o re r a p i d ly in s o i ls t r e a t ed with 2 , 4 -D (D. D. K a u f m a n, u n p u b l i s h ed data). T he i m p o r t a n ce of this o b s e r v a t i on in the f i e l d, h o w e v e r, h as not b e en d e t e r m i n e d. M o b i l i ty T he p l a c e m e nt of a p e s t i c i de on i ts intended t a r g e t - a r ea h as c r e a t ed f ew e n v i r o n m e n t al p r o b l e m s. M o v e m e nt of the p e s- t i c i de f r om its s i te of a p p l i c a t i o n, h o w e v e r, is one c a u se of e n- v i r o n m e n t al c o n t a m i n a t i o n. T h u s, m o b i l i ty data a re u s e f ul in e v a l u a t i ng the p e r s i s t e n ce of a p p l i ed c h e m i c a l s, as w e ll as d e f i n i ng c o n d i t i o ns a s s o c i a t ed with p e s t i c i de u s a g e. in H e r b i c i d es m o ve by l e a c h i n g, w a t er or wind e r o s i o n, and by v o l a t i l i t y. We h a ve a l r e a dy d i s c u s s ed v o l a t i l i ty w h e re a p p l i- c a b le in c o n n e c t i on with i n d i v i d u al c o m p o u n d s. M o v e m e nt of h e r b i c i d es o v er s o il s u r f a c es o c c u rs by w a t er or wind e r o s i o n. T o p o g r a p h y, p e r m e a b i l i t y, and p r e c i p i t a t i on a re i m p o r t a nt f a c- t o rs i n f l u e n c i ng s u r f a ce runoff (Helling and T u r n e r, 1968). S t e ep t o p o g r a p h y, l ow p e r m e a b i l i ty and i n t e n se p r e c i p i t a t i on tend to a c c e l e r a te runoff l o s s es and h e r b i c i de m o b i l i t y. F o r m u l a t i o n, r a te of a p p l i c a t i on and r a i n f a ll i n t e n s i t i es in- l o am f l u e n c ed 2 , 4 -D runoff on a c u l t i v a t e d, f a l l o w, C e c il sandy ( L e G r a n d, 1966). T he i s o o c t yl and b u t y l - e t h er e s t er w e re f ar m o re s u s c e p t i b le to r e m o v al in runoff than the a m i ne s a l t s. L o s s es of 2 , 4 -D w e re p o s i t i v e ly c o r r e l a t ed with the r a te a p p l i e d, w e re g r e a t e st e a r ly in e a ch s t o r m, and d e c r e a s ed with the s t o rm d u r a t i o n. V e g e t a t i ve c o v er a l so i n f l u e n c es s u r f a ce m o v e m e n t. I n i t i al l o s s es of d i c a m ba in runoff w a t er w e re g r e a t- er on sod than on f a l l ow p l o t s; w h e r e as 2 , 4 , 5 -T l o s s es w e re about e q u al ( B a r n e t t, 1967). f o r m u l a t i o ns H e r b i c i de l e a c h i ng i m p l i es the v e r t i c al m o v e m e nt by c a p i l- l a ry and g r a v i t a t i o n al w a t er of a d i s s o l v ed m o l e c u le in the s o il p r o f i l e. A c c o r d i ng to L a G r a nd (1966), l e a c h i ng o c c u rs in the z o ne of a e r a t i on a b o ve the w a t er t a b l e. H e l l i ng and T u r n er (1968) h a ve d e v e l o p ed a s o il t h i n - l a y er c h r o m a t o g r a p h ic t e c h n i q ue f or c h a r a c t e r i z i ng the m o b i l i ty of p e s t i c i d es in s o i l. D i f f e r e n c es in the e f f e ct of s o il type on p e s t i c i de m o b i l i ty h a ve b e en o b s e r v e d. In l i eu of a s t a n d a rd s o i l, t h ey p r e s e n t ed a s y s t em of f i ve c l a s s es of p e s t i c i d es a r r a n g ed on the b a s is of m o b i l i t y. T he m o b i l i ty s c h e me c o m p r i s ed the f o l l o w i ng Rf r a n g e s: C l a ss 1, 0-0.09; C l a ss 2, 0 . 1 0 - 0 . 3 4; C l a ss 3, 0 . 3 5 - 0 . 6 4; C l a ss 4, 0 . 6 5 - 0 . 8 9, and C l a ss 5, 0 . 9 0 - 1 . 0 0. B a s ed on a r e v i ew of the l i t e r a t u re and the w o rk of H e l l i ng (unpublished data) and H e l l i ng and T u r n er (1968), the c o m- m o n ly u s ed t u r f g r a ss h e r b i c i d es could be a s s i g n ed to c l a s s es of d e c r e a s i ng m o b i l i ty as f o l l o w s: C l a ss 5, d i c a m b a, dalapon; C l a ss 4, 2 , 4 - D, 2 , 4 - D P, M C P A, s i l v e x, 2 , 4 , 5 - T; C l a ss 2, b e n s u l i d e, b r o m o x y n i l, D S M A, n e b u r o n, s i d u r o n; C l a ss 1, b e n e f i n, p a r a q u a t, t e r b u t o l, and C l a ss 3, a t r a z i n e, s i m a z i n e. S u m m a ry We h a ve d i s c u s s ed s o me of the c h e m i c a l, b i o c h e m i c al and p h y s i c al w a ys by w h i ch p e s t i c i d es a re d i s s i p a t ed f r om our e n- v i r o n m e n t. D i f f e r e n c es and s i m i l a r i t i es e x i st in how t h e se v a r- i o us p r o c e s s es a f f e ct m a j or c h e m i c al c l a s s es of p e s t i c i d e s. A l t h o u gh we k n ow v e ry l i t t le about the f a te and b e h a v i or of s o me p e s t i c i d e s, c o n s i d e r a b ly m o re i n f o r m a t i on e x i s ts f or m a ny p e s t i c i d e s. Y ou m ay r e c a ll that v e ry f ew of the d e g r a- d a t i ve p a t h w a ys d i s c u s s ed i n v o l v ed c o m p l e te m i n e r a l i z a t i on of the p e s t i c i de to CC>2, H^O, e t c. T he f a te and t o x i c o l o gy of m a ny of the d e g r a d a t i on i n t e r m e d i a t es is unknown. O ur k n o w- l e d ge of the u l t i m a te f a te of p h e n o l i c, a n i l i ne and h e t e r o c y c l ic in s o il is v e ry m e a g e r. A d s o r p t i o n, a b s o r p t i o n, r i ng s t r u c t u r es l e a c h i n g, r u n o f f, wind e r o s i o n, v o l a t i l i t y, c h e m i c al and b i o c h e m- i c al r e a c t i o n s, and p h o t o d e c o m p o s i t i on a re a ll p r o c e s s es w h i ch a f f e ct both the p e r s i s t e n ce and d e g r a d a t i on of t u r f g r a ss h e r b i- c i d es in o ur e n v i r o n m e n t. One or t wo of t h e se p r o c e s s es o f t en p r e d o m i n a te s o i l. P r o p e r t i es of the s o i l, the h e r b i c i de and the e n v i r o n m e nt v a r i a b l es a ct d i r e c t ly and i n d i r e c t l y, and i n t e r a ct in m a ny c o m- b i n a t i o ns to i n f l u e n ce h e r b i c i de b e h a v i o r. in e f f e c t i ng l o ss of a p a r t i c u l ar h e r b i c i de f r om P e s t i c i d es a re not s i g n i f i c a n t ly d i f f e r e nt in p r i n c i p le f r om o t h er c h e m i c al s u b s t a n c es that a re an i n t e g r al p a rt of our c i v- i l i z a t i o n 's e n v i r o n m e n t. T h e ir u l t i m a te d i s p o s a l, j u st as any o t h er c h e m i c a l, m ay p r o d u ce p a r t i c u l ar p r o b l e ms if t h ey p e r- s i s t. T h e re is no r e a s o n, h o w e v e r, w hy m o d e rn t e c h n o l o gy cannot p r o v i de l e ss h a z a r d o us m a t e r i a ls and m o re a d e q u a te and s a fe d i s p o s al t e c h n i q u e s. Such t e c h n i q u es w i ll r e q u i re c o n- tinued r e s e a r ch on the n a t u re of the d e g r a d a t i on of c h e m i c a ls u n d er the v a r i o us e n v i r o n m e n t s. It w i ll a l so r e q u i re a d e q u a te attention to the h a z a r ds to m an and o t h er e l e m e n ts of the e n- v i r o n m e nt d u r i ng the d e g r a d a t i on p r o c e s s. R e f e r e n c es C i t ed A d a m s, D. F ., C. M. J a c k s on and W. L. B a r n e s b e r g e r. 1964. W e e ds 12:280. A e s c h l i m a n n, J. A. and M. R e i n e r t. 1931. J. P h a r m a c o l. E x p t l. T h e r a p. 43:413. A l y, O. M. and S. D. F a u s t. 1964. J. A g r. F o od C h e m. 12:541. Anon. 19 68a. L a wn w e ed c o n t r ol with h e r b i c i d e s. H o me & G a r d en B u l l e t in No. 123. Supt. of D o c u m e n t s, U. S. Govt. P r i n t i ng O f f i c e, W a s h i n g t o n, D. C. A n o n. 19 68b. B e t t er L a w n s. H o me & G a r d en B u l l e t in No. 51. Supt. of D o c u m e n t s, U. S. Govt. P r i n t i ng O f f i c e, Washington, D. C. A s h t o n, F. M. 1965. W e e ds 13:165. B a l d w i n, B. C ., M. F. B r ay and M. J. G e o g h e g a n. 1966. B i o- c h e m. Jour. 101: 15 p. B a r n e t t, A. P ., E. W. H a u s e r, A. W. White and J. H. H o l l a d a y. 1967. W e e ds 1 5 : 1 3 3. B a r t h a, R. and D. P r a m e r. 1967. S c i e n ce 1 5 6 : 1 6 1 7. B a r t h a, R ., R. P. L a n z i i o t ta and D. P r a m e r. 1967. Appl. M i c r o b i o l. 15:67. B a s k i n, A. D. and E. A. W a l k e r. 1953. W e e ds 2:280. B o o e r, J. R. 1944. Ann. Appl. B i o l. 31:340. B o z a r t h, G. A ., H. H. F u n d e r b u r k, J r . a nd E. A. C u r l. 1966. W e ed Soc. A m. A b s t r. p. 55. B r i d g e s, R. G. 1955. J. S c i e n ce F o od and A g r. 6:261. B r o a d h u r s t, N. A ., M. L. M o n t g o m e ry and V. H. F r e e d. 1966. J. A g r. F o od C h e m. 14:585. B u r n s i d e, O. C. and T. L. L a v y. 1966. W e e ds 1 4 : 2 1 1. 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E ., E. J o h n s on and J. L. D e w l e n. 1959. H i l g a r d ia 28:255. E v e r e t t e, C. F. 1963; D i s s e r t a t i on A b s t r. 2 3 : 1 8 5 1. F a u l k n e r, J. K. and D. W o o d c o c k. 1965. J. C h e m. S o c. 1965:1187. F i e l d s, M. L. and D. D. H e m p h i l l. 1966. J o u r. A p p l. M i c r o- b i o l. 14:724. F l i n t, G. W ., J. J. A l e x a n d er and H. P. F u n d e r b u r k. 1963. W e ed S c i. 1 6 : 5 4 1. F o y, C. L. 1960. H i l g a r d ia 30:153. F r i e s e n, H. A. 1965. W e e ds 13:30. G a u n t, J. K. and W. C. E v a n s. 1 9 6 1. B i o c h e m. J. 78:25. G e i s s b u h l e r, H. 1969. D e g r a d a t i on of H e r b i c i d e s. M a r c el D e k k e r, N ew Y o r k. 394 p. G e r s h o n, H. and G. W. M c C l u r e, J r. 1966. C o n t r i b. B o y ce T h o m p s on Inst. 23:291. G o r i n g, C. A. I. 1963. A d v a n. P e s t. C o n t r ol R e s. 5:47. G r a y, R. A. 1962. P h y t o p a t h o l o gy 52:734. H a r r i s, C. I. 1964. 1 2 : 1 1 2. 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P r o c e e d i n gs 7 : 6 7. S h e e t s, T. J. and D. D. K a u f m a n. 1965. P r o c. S o u t h e rn W e ed C o n f. 18:667. S k i n n e r, W. A ., D. E. S t a l l a rd and W. E. P r i d d l e. 1964. A b- s t r a c ts 147th A m. C h e m. S o c. M t g s. A p r il 5 - 1 4, 4 A - 5 A. S k i p p e r, H. D. 1970. P h . D. T h e s i s, O r e g on State U n i v. S k i p p e r, H. D ., C. M. G i l m o u r, and W. R. F u r t i c k. 1967. P r o c. S o il S c i. S o c. A m e r. 3 1 : 6 5 3. S l a c l e, P. 1965. N a t u re 2 0 7 : 5 1 5. S l a d e, P. 1966. W e ed R e s ., 6:158. S m a l l, H. G ., J r. and C. B. M c C a n t s. 1962. T o b a c co S c i. 6:34. S p e n c e r, E. Y. 1965. R e s i d ue R e v. 9 : 1 5 3. S w a n s o n, C. R. 1969. D e g r a d a t i on of H e r b i c i d e s. M a r c el D e k k e r, I n c ., N ew Y o r k. T h o m s o n, W. T. 1967. A g r i c u l t u r al C h e m i c a ls - - B o ok II. H e r b i c i d e s. T h o m s on P u b l i c a t i o n s, P. O. B ox 989, D a v i s, C a l i f. T o r g e s o n, D. C ., D. M. Y o d en and J. B. Johnson. 1 9 5 7. P h y- t o p a t h o l o gy 4 7 : 5 3 6. T r i c h e l l, D. W ., H. L. M o r t on and M. G. M e r k l e. 1968. W e e ds 1 6 : 4 4 7. T u r n e r, N. J. and M. E. C o r d e n. 1963. P h y t o p a t h o l o gy 53:1388. U g o c h u k w u, E. N. and R. L. t r y, (London), p. 35. Wain. 1965. C h e m i s t ry and I n d u s- V l i t o s, A. J. 1952. C o n t r i b. B o y ce T h o m p s on Inst., 16:435. V l i t o s, A. J. 1953. C o n t r i b. B o y ce T h o m p s on Inst., 17:127. V on E n d t, D. W. 1968. J. A g r. F o od C h e m. 1 6 : 1 7. W a i n, R. L. 1963. N a t u re 200:28. W e b l e y, D. M ., R. B. Duff and V. C. F a r m e r. 1959. N a t u re 183:748. W i n t e r i n g h a m, F. P. W ., A. H a r r i s o n, R. G. B r i d g es and R. M. B r i d g e s. 1955. J o u r. S c i e n ce F o od and A g r. 6:251. W o o l s o n, E. A ., J. H. A x l ey and P. C. K e a r n e y. 1 9 7 1. P r o c. S o il S c i e n ce S o c. A m. (Submitted f or p u b l i c a t i o n ). W e ed S c i e n ce S o c i e ty of A m e r i c a. 1967. H e r b i c i de Handbook of the W e ed S o c i e ty of A m e r i c a. W. F. H u m p h r ey P r e ss Inc., G e n e v a, N. Y. 293 p. W u r z e r, B. and F. T. C o r b i n. 1968. Z e i t s c h r i ft f ur P f l a n z e n- k r a n k h e i t an und P f l a n z e n s c h u tz 4 : 17 5. D i s c u s s i on P e r i od D r. S w i t z e r: When studying the a v e r a ge p e r s i s t e n ce of t u r f g r a ss h e r b i c i d e s, what r a t es did you u s e? ( E d i t o r 's Note: T h e se s t u d- i es a re r e p r e s e n t ed in F i g. 1) D r. K a u f m a n: T h e se a re a ll at v a r i a b le r a t e s. R e a l l y, I took a l i t e r a t u re r e v i e w. I did q u a l i fy that, in m a k i ng t h e se a v e r a g e s, I only u s ed r e c o m m e n d ed r a t es f or e a ch compound. T h e re a re no e x c e s s i ve r a t es i n v o l v e d. On the o t h er hand, t h e re could be a d i f f e r e nt r a te of a p p l i c a t i on with dalapon, as o p p o s ed to any o t h er c h e m i c a l. I w as thinking of D C P A, p a r t i c u l a r l y, as o p p o s ed D r. S w i t z e r: to b e n s u l i d e. My e x p e r i e n ce h as b e en that b e n s u l i de and D C PA h a ve about the s a me r e s i d u al a c t i v i ty at c o m p a r a b le r a t e s. Y e t, y o ur g r a ph i n d i c a t ed that D C PA h as a half l i fe of m a y be t wo m o n t h s, w h e r e as b e n s u l i de w as f o ur or s ix m o n t h s. d e r ed if the r a t es f or b e n s u l i de w e re c o m p a r a b le to D C P A. I j u st w o n- D r. K a u f m a n: that t h ey w e re r e c o m m e n d ed r a t es of t h e se c o m p o u n d s. I r e a l ly c a n 't r e c o m m e nd on that, e x c e pt to s ay D r. B i n g h a m: Y ou i n d i c a t ed that 2 , 4 -D s e e m ed to t r a v el a l m o st as f ar into the s o il as d i c a m b a. We h a ve the p r o b l em with d i c a m ba getting into the root s y s t e ms of m a ny p l a n t s, l i ke o r n a m e n t a l s. don't we h a ve the s a me p r o b l e m? If 2 , 4 -D g o es in the s o il to this depth, too, w hy I would s ay it w as a m a t t er of d e g r a d a t i o n. F r om It D r. K a u f m a n: my own v i e w p o i nt as a m i c r o b i o l o g i s t, I think of 2 , 4 -D as being a r e a d i ly d e g r a d a b le compound. T h is h as b e en d e m o n s t r a t e d. is a v e ry d e g r a d a b le compound. D i c a m b a, in c o n t r a s t, is not r e a d i ly d e g r a d e d. We h a ve l o o k ed f or a long t i me f or an o r g a n i sm that would d e g r a de t h is compound. l e a st r e s i s t a nt to m i c r o b i al d e g r a d a t i o n, u s i ng a c h l o r i de as a m a j or d e g r a d a t i o n. We w e re only u s i ng c h l o r i de ion ation. should be the s a me as d i c a m b a. ion l i b e r- In a s i t u a t i on w h e re you h a ve 2 , 4 -D l e a c h i ng it, the e f f e ct In the f u s i on s y s t e m, it is at It wouldn't be t a k en up. I w o n d e r ed if t h is thin l a y er s y s t em g a ve you s i m i- D r. B i n g h a m: l ar r e s u l ts that you would find in the f i e ld situation. M a y be s o m e t h i ng l i ke 2 , 4 , 5 - T. Is t h is d e g r a d i ng as f a st as 2 , 4 - D? C o u ld we get d i f f e r e n c es with the v a r i o us p h e n o x ys ? D r. K a u f m a n: D i f f e r e n ce of w h a t - - p e r s i s t e n c e? D r. B i n g h a m: Y e s, and a l so the e f f e ct on o r n a m e n t a ls or plants that h a ve s h a l l ow root s y s t e m s. d i c a m ba and p h e n o xy h e r b i c i d es on o r n a m e n t al plants f o l l o w i ng t u rf a p p l i c a t i o ns m o re r e l a t ed to uptake and t r a n s l o c a t i on d i f f e r- e n c e s, than d e g r a d a t i o n? Is the d i f f e r e n ce b e t w e en I think t h e re is v e ry d e f i n i t e ly a d i f f e r e n ce in D r. K a u f m a n: t he p e r s i s t e n c e, at l e a st in t e r ms of m i c r o b i o l o g y. T h e re would be a d i f f e r e n ce in the p e r s i s t e n ce of 2 , 4 , 5 - T. p e r s i s t e nt to d e g r a d a t i o n. T h e re is a lot k n o wn about s t r u c t u re e f f e c ts h e r e, and a n y t i me y ou put s o m e t h i ng in a n o t h er p o s i t i o n -- o b v i o u s ly the p h e n o xy compound should be in the 3 or 5 p o s i t i o n -- y ou i m p a rt r e s i s t a n ce to d e g r a d a t i o n. It is m u ch m o re P R A C T I C AL T O X I C O L O GY IN C O N S U M ER U SE OF T U R F G R A SS H E R B I C I D ES J a m es E. D e w ey D e p a r t m e nt of E n t o m o l o gy C o r n e ll U n i v e r s i ty I t h a c a, N ew Y o rk 14850 I n t r o d u c t i on My c o n t a ct with p e o p l e, r e l a t i ve to h e r b i c i d e s, is an i n d i- I!m not a t u rf m a n, n or a h e r b i c i de s p e c i a l i s t. M a ny r e ct one. of t h o se u s i ng h e r b i c i d e s, in my opinion, f e el that h e r b i c i d es r e a l ly a re not p e s t i c i d e s. but p e r h a ps s m e ll d i f f e r e n t l y. S o me of the r e s e a r ch p e o p le work-! ing with h e r b i c i d es e v i d e n t ly h a ve s i m i l ar T h ey f e el t h ey a re m o re l i ke w a t e r, i d e a s. T o x i c i ty S t u d i es T he b a s is of t o x i c o l o gy g o es b a ck to the r e l a t i o n s h ip of d o se to r e s p o n s e. T y p i c a l l y, we s p e ak of a c u te o r al d o s e s; c h r o n ic or s u b - a c u te d o s es i n v o l v i ng r e p e a t ed d o s es o v er an e x t e n d ed p e r i o d; d e r m al d o s es to the skin, and inhalation. A ll of y ou a re w i th e x p r e s s i o ns of t o x i c i t i es of this t y p e. O r a l, c h r o n i c, d e r m a l, e ye i r r i t a t i o n, b i r th d e f e c t s, e t c ., a re a ll a p a rt of the t o x i c o l o gy i n f o r m a t i on n e e d ed to obtain r e g i s t r a t i on of a p e s t i c i d e. P r e l i m i- n a ry c h r o n ic or s u b - a c u te t o x i c i t i es u s u a l ly c o n s i st of 90 d ay f e e d- ing s t u d i e s, and at l e a st 21 d a ys f or i n h a l a t i o n, u s i ng guinea p i g s. Inhalation s t u d i es a re u s u a l ly b a s ed on e x p o s u re to v a p o r s, and g e n e r a l ly h a ve not i n c l u d ed e x p o s u re to a e r o s ol d r o p l e ts or o t h er p a r t i c u l a te m a t t e r, u n l e ss the f o r m u l a t i on s t u d i ed h a p p e ns to be s p e c i f i c a l ly f or u se as an a e r o s o l. f a m i l i ar With the n e ed for. e s t a b l i s h i ng t o l e r a n c es f or a ll c o m p o u n d s, c h r o n ic t e s ts a re the r u l e. H o w e v e r, in the p a st t h is w as not s o, p a r t i c u l a r ly with h e r b i c i d es and f u n g i c i d e s. T wo y e ar c h r o n ic o r al s t u d i es a re now s t a n d a r d, u s u a l ly u s i ng r a t s, s o m e t i m es d o g s, and o c c a s i o n a l ly m o n k e y s. O c c a s i o n a l ly t h i rd g e n e r a t i on a n i m al P r o- s t u d i es f or e f f e c ts on r e p r o d u c t i on a re now r e q u i r e d. b a b ly e v en m o re t e s ts of t h is s o rt w i ll be r e q u i r ed in the f u- t u re - u s i ng m i c e. We m ay a l so u se e gg e m b r yo t e s ts to d e- t e ct t e r a t o g e n e t ic e f f e c t s. C o st of s u ch t e s ts a re high b e c a u se of the n u m b er of a n i m a ls r e q u i r ed and the e x t e n d ed t i me v o l v e d. i n- W i l d l i fe t o x i c i ty is a l so an i n t e g r al p a rt of o ur t o x i c i ty s t u d i e s. In the p a s t, t h is h as not b e en t r u e. T he s t a n d a rd p r o- c e d u re p r e s e n t ly i n v o l v es t h r ee s p e c i es of f i sh and t h r ee s p e- c i es of b i r d s. P e o p le i n t e r e s t ed in w i l d l i fe o f t en a sk why t o x i- c i ty t e s ts a re not c o n d u c t ed on e a g l e s, the o s p r ey and s e v e r al o t h er b i r d s. O b v i o u s ly t e s ts c a n 't be run on e v e r y t h i n g, and a n i m a ls h a ve to be s e l e c t ed that a re r e a d i ly a v a i l a b le in f a i r ly l a r ge n u m b e r s. We don't h a ve a ll the a n s w e r s, but m u st p r o- c e ed on a c a l c u l a t ed r i sk b a s is j u st as we do w h en we c r o ss the s t r e e t. F e e d i ng s t u d i es h a ve long b e en r e q u i r ed f or p e s t i c i d es u s ed on f o od c r o ps p r i or to r e g i s t r a t i o n, but n o n - f o od u s es s o m e t i m es e s c a p e d. T h e se a re now a p a rt of the r o u t i ne f or a ll p e s t i c i d e s, r e g a r d l e ss of u s e. In the f u t u re m o re of the a n s w e rs r e l a t i ve to w a rm b l o o d ed a n i m a ls w i ll be n e e d e d. T h i s, of c o u r s e, i n v o l v es i n c r e a s i n g ly r e f i n ed a n a l y t i c al t e c h n i q u e s. In the l a te 1 9 4 0 ' s, a s e n s i t i v i ty of 2 p pm f or D DT w as c o n s i d e r ed good. Anything l e ss than t h is w as c o n s i d e r ed as z e r o. Now we a re w o r k i ng p a r ts p er b i l l i on and p a r ts p er t r i l l i on l e v e ls and s t i ll s o m e t i m es s e e k i ng to go l o w e r, p a r t i c u l a r ly with w a t er c o n t a m i n a t i on p r o- b l e ms and e f f e c ts on w i l d l i f e. in T he i m p o r t a n ce of r e a d i ng the l a b el h as b e en s t r e s s ed to in- a v o id f a t al a c c i d e n t s. U n f o r t u n a t e l y, m a ny of the c h i l d r en v o l v ed in s u ch a c c i d e n ts cannot r e ad and the p a r e nt or an adult h as f a i l ed to c o m p ly with the l a b e l. I am now about at the point w h e re I think i t 's an e f f o rt in f u t i l i t y. P e o p le j u st don't r e ad l a b e l s. C l a s s es of T o x i c i ty P e s t i c i de p r o d u c ts h a ve b e en g r o u p ed into f o ur c l a s s e s, d e p e n d i ng on t h e ir t o x i c i ty f or l a b e l i ng p u r p o s e s. C l a ss I p e s- t i c i d es a re h i g h ly t o x i c, b a s ed on o r al t o x i c i t i es to 50% of the . 1 E L B A T N O I T A R T S I N I M D A F O E T U O R Y T I C I X O T F O S E I R O G E T A C - T C A E D I C I T N E D O R D N A E D I C I G N U F E D I C I T C E S N I L A R E D E F 0 5 C L N O I T A L A H N I L A M R E D 1 ) g k / g m ( 0 5 P L e s o D l a r O y l b a b o r P L A R O D R O W L A N G I S 2 ) l / g u ( e r u s o p x e . r h 4 2 n a m . b l 0 5 1 a r o f 1 ) g k / g m ( L E B A L E H T N O Y R O G E T A C o t 0 0 0 , 2 r e v o o t 0 0 2 r e v o l u f n o o p s a e t e n o r e v o o t 0 5 r e v o G N I N R A W I I 0 0 0 , 0 2 0 0 0 , 2 e c n u o e n o o t 0 0 5 ) C I X O T Y L E T A R E D O M ( 0 0 0 , 2 o t 0 0 0 2 o t 0 a o t s p o r d w e f a 0 5 o t 0 l l u k s - R E G N A D I N O S I O P l u f n o o p s a e t - s e n o b s s o r c d n a ) C I X O T Y L H G I H ( o t 0 0 0 , 2 r e v o e n o o t e c n u o e n o r e v o 0 0 5 r e v o N O I T U A C I I I 0 0 0 , 0 2 d n u o p e n o r o t n i p 0 0 0 , 5 o t ) C I X O T Y L T H G I L S ( 0 0 0 , 0 2 r e v o e n o r o t n i p e n o r e v o 0 0 0 , 5 r e v o * e n o n I V d n u o p ) C I X O T N O N Y L E V I T A L E R ( h c i h w n o i t a r t n e c n o c r i a e h t - 0 5 C L l l i k l l i w h c i h w l e v e l e s o d e h t - 0 5 D L n o d e s a b d e r i u q e r e n o N * " : E T O N - n M i . r u o h 1 f o d o i r e p a r o f d e s o p d e t s a f s l a m n A i . n o i t a v r e s b o s y a d y a m n r e t t a p e s u d n a t c u d o r p f o , n o i t a v r e s b o s y a d 4 1 f o m u m i . s e i d u t s l a r o r o f - n o i t u a c e r p e t a i r p o r p p a e r i u q e r n i d e s s e r p x e e b y a m s a g r o r o p a V . m p p s t n e m e t a t s y r a ) b l ( s d n u o p 2 . 2 ) g k ( m a r g o l i k 1 ; e c n u o 1 s m a r g 3 . 8 2 ; ) g ( m a r g 1 ) g m ( s m a r g i l l i m 0 0 0 1 : s t n e l a v i u q E 1 ) g m ( m a r g i l l i m 1 ) g u ( s m a r g o r c i m 0 0 0 1 ; s t r a u q 6 0 . 1 ) 1 ( r e t i l 1 : s t n e l a v i u q E 2 - x e s l a m n a i t s e t f o % 0 5 l l i k l l i w 4 1 f o m u m n M i i . s l a m n a i t s e t f o % 0 5 e r u t a n , r e v e w o h ; y t i c i x o t e t u c a a n i m a ls e x p o s e d, u s u a l ly r a t s, of d o s es of 50 m i l l i g r a ms p er k i l o g r am or l e s s; i n h a l a t i on of not o v er 200 ppm and skin a d- s o r p t i on of 200 ppm. ( P l e a se r e f er to T a b le 1 f or a s u m m a ry of c a t e g o r i es of t o x i c i t y .) l e g i s l a t i on in N ew Y o rk p a s s e s, a ll C l a ss I p o i s o ns w i ll be on t he r e s t r i c t ed l i st and w i ll not be a v a i l a b le to the g e n e r al pub- l i c. T h ey w i ll be s o ld only by v e n d o rs h a v i ng p e r m i ts and p u r- c h a s ed only by p e o p le that h a ve u se p e r m i t s. But the u s es of t h e se m a t e r i a ls w i ll not be l i m i t e d, t h ey c an be u s ed f or any of the l a b e l ed u s e s. If our p r o p o s ed n ew r e s t r i c t ed S o me h e r b i c i d es a re h i g h ly t o x ic and a re in C l a ss I; i . e ., the d i n i t r o s, e n d o t h a ll and s o d i um a r s e n i t e. P e s t i c i d es in C l a ss I h a ve l a b e ls b e a r i ng the s i g n al w o r ds " D a n g e r - P o i s o n" a n d / or the s k u ll and c r o s s b o n e s. C l a ss II p e s t i c i d es h a ve m o d e r a t e ly high t o x i c i t i e s, 50 to 500 l i ke diquat, p a r a q u at and p e n t a c h l o r o p h e n ol a re m i l o g r a ms p er k i l o g r a m, and h a ve the w o rd " W a r n i n g" on the l a b e l. M a t e r i a ls e x a m p l es of h e r b i c i d es in t h is c a t e g o r y. T he w a r n i ng on the l a b el is m u ch m i l d er than on the C l a ss I p e s t i c i d e s. T he l a b el of a p r o- duct in t h is c a t e g o ry w a r ns a g a i n st inhaling, c a u t i o ns a g a i n st g e t- ting it on the skin, t a k i ng it i n t e r n a l l y, and k e e p i ng it out of the r e a ch of c h i l d r e n. G e n e r a l l y, t h is c a t e g o ry of m a t e r i a ls is thought, e v en by r e s p o n s i b le i n d u s t r y, to be too t o x ic f or g e n e r al a v a i l a b i l- i ty to the a v e r a ge h o m e o w n e r. As a m a t t er of p r a c t i ce we do not p r e s e n t ly r e c o m m e nd to the g e n e r al h o m e o w n er a u d i e n ce anything but C l a ss 3 and C l a ss 4 c o m p o u n d s, with f ew e x c e p t i o ns w h i ch we c a ll s p e c i a l i z ed u s e s. C l a ss 3 c o m p o u n ds b e ar the s i g n al w o rd " C a u t i o n ." T he p r i n- c i p le p r o b l em with C l a ss 3 p e s t i c i d es is not f r om g e n e r al e x p o s u re of the u s e r, but f r om s t o r i ng t h em in u n m a r k ed c o n t a i n e r s, so a re l a t er m i s u s e d. T h e re is a n e ed to t r e at a ll p e s t i c i d es with r e s p e c t. As long as p e s t i c i d es a re t r e a t ed as p o i s o n s, d i f f i c u l ty c an be a v o i d e d. t h ey C l a ss 4 p e s t i c i d es do not r e q u i re any w a r n i ng or s i g n al w o rd on the l a b el and a re c o n s i d e r ed to be r e l a t i v e ly s a f e; that i s, as s a fe as a p e s t i c i de c an be. E x a m p l es of t h e se t y p es of m a t e r i a ls a re dalapon, s i m a z i ne and a m i t r o l e. In spite of the f a ct that a m i- t r o le is a C l a ss 4 m a t e r i a l, one that we think is r e l a t i v e ly s a f e, the F o od and D r ug A d m i n i s t r a t i on h as r e f u s ed to i s s ue a t o l e r- a n ce f or the m a t e r i al b e c a u se of p o s s i b le c a r c i n o g e n i c i t y. T h is a c t i on h as b e en p e t i t i o n ed by the A m e r i c an C y a n a m id C o m p a ny and A m c h em P r o d u c t s, Inc., and a f a ct finding c o m m i t t ee h as b e en appointed. T h is is one of the t y p es of p r o b l em that w i ll be e n c o u n t e r ed m o re and m o r e. m a ke us v e ry c a r e f ul in our p r e s e n t a t i on to the p u b l ic if we a re to m a i n t a in o ur c r e d i b i l i t y. We m u st not s ay that t h ey a re h a r m- l e ss m a t e r i a l s. B e t t er m e a ns f or r e e v a l u a t i ng m a t e r i a ls as our s t a n d a r ds change a re n e e d e d. I t 's the s o rt of thing that should E v a l u a t i ng D a ta on P e s t i c i d es One of the d i f f i c u l t i es e n c o u n t e r ed is the f a i l u re to r e c o g- n i ze that the s t a n d a r ds by w h i ch j u d g e m e n ts h a ve to be m a de a re c h a n g i n g. As a r e s u l t, we h a ve b e en l o s i ng our c r e d i b i l i t y. One of the r e a s o ns is that o f t e n t i m es i n d u s t ry h as t a k en the attitude that the b e n e f i ts o v er the r i s ks a re p r o v ed beyond any doubt. L i k e w i s e, we h a ve e x p e c t ed our c r i t i cs to p r o ve us w r o ng beyond a ny doubt. On the o t h er hand, p e o p le that h a ve c r i t i c i z ed the i n- d u s t r y, l i ke the E n v i r o n m e n t al D e f e n se Fund and o t h e r s, h a ve t a k en the attitude that the s l i g h t e st s h r ed of e v i d e n ce is a m p le to r a i se a q u e s t i on and is of s u f f i c i e nt r e a s on to k e ep a p e s t i c i de off the m a r k e t. the e n v i r o n m e nt and a l so to m a ke c e r t a in that p e s t i c i d es a re a v a i l a b l e, m u st be r e c o g n i z e d. D a ta m u st be e v a l u a t ed as f a i r ly as p o s s i b le and l et the c h i ps f a ll w h e re t h ey m a y. If t h e re is a r e a s o n a b le doubt or q u e s t i o n, and t h e re a re a l t e r n a te m e t h o d s, t h en the only p r u d e nt thing is to u se t h e se a l t e r n a t i ve We m u st r e a d j u st our thinking and m a ke c h a n g es as t h ey o c c ur r a t h er than w a it f or t h em to be f o r c ed upon u s. In d e a l i ng w i th t h is p r o b l e m, the n e ed to p r o t e ct m e t h o d s. When a c h e m i st or c o n s e r v a t i o n i st s t a r ts m a k i ng j u d g e m e n ts on w h e t h er or not D DT is c a r c i n o g e n i c, I think h e 's out of h is f i e l d. I l i k e w i se f e el h e 's out of h is f i e ld if he s t a r ts t a l k i ng about o x y g en p r o d u c t i on and a l g ae in the o c e an w h en he h a s n 't gotten b e- yond the t e st tube s t a g e. T he j u d g e m e n ts on p u b l ic h e a l t h, s u ch as c a r c i n o g e n i c i t y, t e r a t o g e n i c i ty and m u t a g e n i c i t y, should be m a de by p e o p le w o r k i ng in t h is f i e l d. T he F o od and D r ug A d m i n i- s t r a t i on and P u b l ic H e a l th D e p a r t m e nt h a ve t h e se r e s p o n s i b i l i t i e s. A l s o, o t h er p r o f e s s i o n al g r o u ps a re c a p a b le and r e s p o n s i b l e. F or e x a m p l e, a f i ve m an c o m m i t t ee of the A m e r i c an M e d i c al A s s o c i- a t i on r e p o r t ed in i ts M ay 1 1, 1970, J o u r n al that the p r o of of D DT b e i ng a c a r c i n o g en is not c o m p l e te and is s o m e t h i ng that s t i ll h as to be e s t a b l i s h e d. If t h e re h a s n 't b e en any a c t i o n, then s o m e o ne had b e t t er I don't k n o w, f r a n k l y, how m u ch a c t i on h as b e en t a k en on w a rm b l o o d ed a n i m a l s, or the e f f e ct c a r b a m a t es h a ve on m i t o- s i s. i n s t i g a te s o me r e s e a r ch i m m e d i a t e l y. A l s o, I think that w e, as plant s c i e n t i s t s, p r o b a b ly shouldn't be t a l k i ng too m u ch about the h a r m l e ss n a t u re of t h e se k i n ds of m a t e r i a l s, r e l a t i ve to m i- t o t ic e f f e c t s, if we do not h a ve e v i d e n c e. O ur state and f e d e r al a g e n c i es a re not a l w a ys s e n s i t i ve to the n e e ds of the p u b l ic and a c c e p t i ng r e s p o n s i b i l i ty or a s s u m i ng l e a d e r s h i p. T he P e s t i c i de R e g u l a t i on D i v i s i on is o p p o s ed to the i d ea of the l e g i s l a t i ve a c t i v i ty of the s t a t e s. But w hy a re the s t a t es doing it? One of the r e a s o ns is b e c a u se a n e ed is not b e- ing m e t. As a r e s u l t, the s t a t es h a ve b e en f o r c ed to t a ke a c t i on of t h e ir own. T h is is u n d o u b t e d ly going to r e s u lt in a c e r t a in a m o u nt of c h a o s. M u ch of this could h a ve b e en a v o i d ed s ix to e i g ht y e a rs a go if we had b e en s e n s i t i ve to s o me of the f a c ts w h i ch w e re as e v i d e nt then as t h ey a re t o d a y, and r e s p o n d ed w i th s o me a c t i on to c u r t a il the u s es of m a t e r i a ls l i ke D DT and d i e l d r i n. We m u st c h a n ge our attitude or we w i ll c o n t i n u a l ly f i nd o u r s e l v es in s i t u a t i o ns of t h is s o r t. P e s t i c i d es and P u b l ic H e a l th If we a r e n 't going to We m u st be m o re c r i t i c al of p e s t i c i d es and t h e ir e f f e c ts on h e a l th and the e n v i r o n m e n t. Who h as any m o re r i g ht to be c r i t i c al of p e s t i c i d es than w e? We a re w o r k i ng with l i c e n s ed and e x p e r i m e n t al m a t e r i a ls a ll the t i m e. be c o n c e r n e d - - we who a re w o r k i ng w i th t h e m, the o n es that k n ow the m o st about t h e m - - t h en I think we a re not m e e t i ng our r e s p o n s i b i l i t i e s. We m u st a s s u me t h is r e s p o n s i b i l i ty and e v a- l u a te t h e se c o n d i t i o ns m o re c a r e f u l l y. T h e re a re f ew u s es that a re so g r e at that t h ey would t a ke p r e c e d e n ce o v er the public h e a l t h. T he public is now s a y i ng that o ur s t a n d a r ds h a ve b e en too l a x; that t h ey don't l i ke s o me of the d e c i s i o ns we h a ve m a d e. If we a r e n 't going to be s e n s i t i ve to t h e ir n e e ds and r e s p o nd a c- c o r d i n g l y, t h e y ' re going to t a ke the d e c i s i o ns out of our h a n d s. T he f a ct that P RD and F DA a re both being t r a n s f e r r ed to a n ew E n v i r o n m e n t al P r o t e c t i on A g e n cy is s t r o ng e v i d e n ce of t h i s. We tend to t a lk to our own g r o u p s, t e ll how w i ld the o t h er g uy i s, and s y m p a t h i ze with one a n o t h e r. O t h er g r o u p s, in t u r n, do the s a me thing. U n f o r t u n a t e l y, as long as this s i t u a t i on e x- i s t s, p r o b l e ms w i ll continue. We m u st c o m m u n i c a te with one a n o t h er to obtain u n d e r s t a n d i n g. If an e f f o rt i s n 't m a de to s ee that the b i rd w a t c h er is a w a re of the p u r p o s es and the n e ed f or p e s t i c i d e s, h e 's not going to c a re u n t il it a f f e c ts h im p e r s o n a l l y. C o n t r ol of P e s t i c i d es I w o n d er how m a ny of you h a ve stopped to think about how the p e s t i c i de i n d u s t ry i m a ge h as b e en b r o u g ht about. We t a lk a b o ut r e g i s t r a t i o ns of p e s t i c i d e s; how d i f f i c u lt t h ey a re to obtain and h ow m u ch m o re p e st c o n t r ol we n e e d. As of t h r ee y e a rs a g o, the r e g u l a t i o ns n e c e s s a ry in this c o u n t ry to r e g i s t er a p e s- t i c i de a re m o re s t r i n g e nt than t h o se r e q u i r ed f or m o st of o ur f o od a d d i t i v es and m a ny of our d r u g s. T h is d o es not m e an that the p r o b l em of s a f e ty to h e a l th h as b e en r e s o l v e d. In f a c t, our p r e s e nt s t a te a f f a i rs is a m p le e v i d e n ce that we h a ve not s o l v ed t h e m. One of the r e a s o ns f or the p r e s e nt d i f f i c u l t i es is that p e s t i- c i d es a re e x t r e m e ly w e ll c o n t r o l l ed and r e s e a r c h ed up the point of m a r k e t i n g. H o w e v e r, f r om the m a r k et p l a ce to t h e ir f i n al t h e re is l i t t le c o n t r ol and anything c an happen. T he P e s t i c i de R e g u l a t i o ns D i v i s i on d o es not l a b el s o me of our m o re t o x ic m a- t e r i a ls f or h o me g a r d en u s e. N or do t h ey intend t h em f or h o m e- o w n er u s e, but the h o m e o w n er c an p u r c h a se t h em at the c o m m e r- c i al o u t l e t s. T h is i s, of c o u r s e, one of the r e a s o ns f or the l e g i s- l a t i on to r e s t r i ct the s a le of h i g h ly t o x ic C l a ss I m a t e r i a l s. u se O ur i m a ge r e a l ly h as b e en c r e a t e d, not by what w e ' ve done p r i or to m a r k e t i n g, but w h at h a p p e ns to the p e s t i c i de a f t e r w a r d s. W ho ends up u s i ng m o st of the p e s t i c i d e s? Is it the h i g h e st paid m a n, the m a n a g er or the m o st k n o w l e d g e a b l e? U s u a l ly i t 's the m o st p o o r ly p a i d, p o o r ly e d u c a t ed i n d i v i d u al on the t e a m. If we w i sh to continue to o p e r a te t h is w a y, we h a ve only one a l t e r n a t i v e. We m u st go to the s a f e st p o s s i b le m a t e r i a ls and s a c r i f i ce good c o n t r o l. We a ll tend to r e s i st the i d ea of a p r e s c r i p t i on type of o p e r a t i o n, as p r a c t i c ed by the v e t e r i n a r i an or m e d i c al d o c t o r. B ut n e i t h er the v e t e r i n a r i an n or the M . D. is in the spot with p r e s c r i p t i on m e d i c i n es that w e ' re in at p e s t i c i d e s. B o th a re u s i ng m a t e r i a ls that a re in m a ny j u st as d a n g e r o u s, although t h ey a r e n 't u s ed on quite the b r o ad s c a le or quantity. H o w e v e r, the b a s ic p r o b l em is v e ry s i m i l a r. the p r e s e nt t i me with i n s t a n c es To c o r r e ct the s i t u a t i o n, m o re c o n t r ol is n e e d ed f or the p e o p le who u se p e s t i c i d e s, m a k i ng s u re that t h ey a re b e t t er i n- f o r m e d. We c an c o n t r ol the m a t e r i a ls w h i ch t h e se p e o p le u s e. F or e x a m p l e, of the 18 m i l l i on p e o p le in the state of N ew Y o r k, o n ly t wo out of e v e ry h u n d r ed a re in a g r i c u l t u re or a s s o c i a t ed a g r i c u l t u r al b u s i n e s s e s. T he r e st of the p u b l ic f e el t h ey don't n e ed p e s t i c i d es in spite of the f a ct that p r o b a b ly 80% to 90% of t h e se p e o p le u se t h em in t h e ir h o m e s. T h ey do not think of t h e se m a t e r i a ls as being a g r i c u l t u r al as t h o se that t h ey a re c r i t i c i z i n g; i . e ., D D T. M o st of t h em w o u l d n 't a d m it or don't k n ow that t h ey e v er u s ed D D T, although t h ey p r o b a b ly h a ve the a e r o s o ls that c o n t a in it u n d er the k i t c h en s i n k. If t h ey do r e a l i ze t h ey h a ve it, t h ey a re i n c l i n ed to think t h at the s m a ll a m o u nt t h ey h a ve d o e s n 't c o n t r i b u te to the p r o- b l e m. c h e m i c a ls and the s a me S o me t r o ut f r om L a ke G e o r ge h a ve b e en found with r e s i d u es of D DT as h i gh as 146 p p m. T h e re is no a g r i c u l t u re in the a r e a. M o st of the D DT u s ed in the a r ea w as by the State C o n s e r v a t i on D e p a r t m e n t, but t h ey h a v e n 't u s ed any s i n ce 1962. t h i s, the l e v e ls h a ve continued to i n c r e a se m e a ns that the t o u r i s ts and c o t t a ge o w n e rs l i v i ng a r o u nd the l a ke a re the only o t h er p o s s i b le p l a ce that D DT could h a ve c o me f r o m, u n l e ss i t 's f a l l - o ut f r om the a i r. in t h e se f i s h. T h is In spite of I t 's not going to be e a sy f or us to c h a n ge o ur outlook, but if we a re going to be r e a l i s t i c, we m u st c h a n g e. W e ' ve b e en on t he d e f e n s i ve f or s e v e r al y e a rs and w h e re h as it gotten u s? If t h is c o n t i n u e s, w e ' re going to l o se a ll of o ur o p p o r t u n i t i es to i n f l u e n ce p e s t i c i de d e c i s i o n s. T he only w ay we c an g a in r e s p e ct and i n f l u e n ce what p e s t i c i d es c an be u s ed and the p a rt t h ey c an p l ay is to w i l l i n g ly a d m it our m i s t a k es or the p o s s i b i l i ty of h a r m f ul e f f e c t s, and t ry to e s t a b l i sh c r e d i b i l i t y. L a ck of C o m m u n i c a t i o ns T he q u e s t i on is h ow to get the f a c ts to a m a ss a u d i e n c e. M o st of you r e m e m b er 2 , 4 , 5 -T r e p o r ts f r om G l o b e, A r i z o n a. A b o ut one t h i rd of the i n s i de p a ge of the f i r st s e c t i on of the N ew Y o rk T i m es w as d e v o t ed to 2 , 4 , 5 -T and a ll the d i s t o r t i o ns that o c c u r r ed to m a n, a n i m a l, p l a n t s, e t c. T h r ee or f o ur w e e ks l a t e r, on about p a ge 7 8 of S e c t i on 4, down in the l o w er l e ft hand c o r n er of the r i g ht hand p a g e, t h e re w as a t h r ee i n ch a r t i c le pointing out that a t a sk f o r ce sent to i n v e s t i g a te the 2 , 4 , 5 -T i n- c i d e nt found the f a c ts not to be s u b s t a n t i a t e d, e x c e pt f or m i n or d i s t o r t i on of a f ew p l a n t s. M o st a u d i e n c es I h a ve t a l k ed to a ll h a ve s e en the o r i g i n al r e p o r t, b e l i e ve it, but a l m o st none h a ve s e en the a r t i c le a p p e a r i ng t h r ee w e e ks l a t er r e p o r t i ng w e re not the f a c t s. w ay to a c q u a i nt the public with the f a c ts of the Is this r e s p o n s i b le r e p o r t i n g? t h e se Is t h is the i s s u e? T he point i s, the n e ws m e d ia a re s e l l i ng n e w s. M a ny do not s e em to be i n t e r e s t ed in f a c t u al s t o r e s - - t he p r os and c o n s - - so the m an on the s t r e et c an m a ke a sound d e c i s i o n. T h e y1 re t e r e s t ed in w h a t 's going to s e ll the n e w s p a p e r, or n e ws p r o g r a m. U s u a l l y, t h is is s o m e t h i ng t h a t!s d i f f e r e nt and w i ll c a t ch h is a t- t e n t i o n. i n- One of the b i g g e st c h a l l e n g es that the u n i v e r s i t i es and i n- d u s t ry h a ve in the f u t u re is h ow t h ey i n f o rm the p u b l ic a d e q u a t e- ly to m a ke a f a ir d e c i s i o n. h a ve c o n f i d e n ce that the r i g ht d e c i s i o ns w i ll be m a d e. If t h ey do not h a ve t h e se f a c t s, t h ey h a ve no a l t e r n a t i ve but to b e l i e ve w h at is r e l e a s ed by the n e ws m e d i a. If we c an get the f a c ts to t h e m, I D i s c u s s i on P e r i od D r. A l l e y: Y ou s ay we a re the o n es that a re getting o u r s e l v es I don't b e l i e ve into a c o r n er f r om p e s t i c i de r e c o m m e n d a t i o n s. t h is is so. I think e v e r y o ne of us w o r k i ng with any f o rm of p e s- t i c i de h a ve t r i ed to t e ll the p u b l ic a ll along what we know about t h e m. D r. D e w e y: Y o ur c o m m e n ts a re w e ll t a k e n. As you k n o w, t h e re a re t h r ee k i n ds of pollution: p e s t i c i d e, p o l i t i c al and e m o t i o n a l. In s o me i n s t a n c es the p o l i t i c al and the e m o t i o n al a s p e c ts a re m u ch g r e a t er than o ur a c t u al p e s t i c i de pollution. One of the m o st d i s c o u r a g i ng t h i n gs is to s ee the u t t er c h a os that e x i s ts P RD and F D A. T h is is the r e s u lt of d e c i s i o ns not being m a de I d a re s ay that by the t e c h n i c al p e o p le that h a ve the i n f o r m a t i o n. 2 , 4 , 5 -T is a c a se of point. T h is is a s u b j e ct of g r e at i n t e r e st and I am not w e ll enough i n f o r m ed to d i s c u ss it. H o w e v e r, I ' ve y et to s ee the s c i e n t i f ic p a p er on w h i ch the f i n al j u d g e m e nt w as m a d e. in M a ny of us h a ve o f t en s a id that t h e se m a t e r i a ls w e re not h a r m f ul and that we didn't think t h e re w as any h e a l th p r o b l e m. Y ou m ay h o n e s t ly s t i ll f e el t h is w a y, but I w o n d er if m a y be what we should s ay is that t h is is an a r ea o u t s i de o ur r e a lm of r e s p o n s i b i l i t y. H e a l th a s p e c ts a re e s t a b l i s h ed by F D A, or a g e n c y. the a p p r o p r i a te h e a l th It i s n 't a h e r b i- T h e re W e ' ve had r e p o r ts of c a p t an being t e r a t o g e n i c. c i d e, so we c an t a lk about it a l i t t le m o re i m p a r t i a l l y. h a ve b e en s e v e r al a r t i c l es in the N ew Y o rk T i m es on the c h a r- a c t e r i s t i cs of t h is p a r t i c u l ar m a t e r i a l. T he F DA r e d u c ed the t o l e r a n ce 50% but, as n e ar as I c an d e t e r m i n e, t h is r e d u c t i on w as not b a s ed on the h a z a rd of t e r a t o g e n i c i t y. the f a ct that the l e v e ls being u s ed w e re only about o n e - h a lf as g r e at as t h ey o r i g i n a l ly a n t i c i p a t e d. T he r e s i d ue l e v e ls w e re l ow enough so that h i g h er t o l e r a n c es w e re not n e e d e d. T h is is the d e c i s i on of the g o v e r n m e nt g r o u ps c h a r g ed with t h is r e s p o n- s i b i l i t y. L e t 's put the r e s p o n s i b i l i ty w h e re it b e l o n g s. m a de a m i s t a k e, w hy should we a d s o rb i t? At the s a me t i m e, I think the p u b l ic w i ll r e c o g n i ze that we a re being m o re h o n e st a b o ut the situation, and t h is w i ll i m p r o ve o ur c r e d i b i l i t y. It w as b a s ed on If t h e y ' ve D r. A p p l e b y: Y ou m e n t i o n ed b r i e f ly that we had m a de m i s t a k es in the p a st that tend to c r e a te a c r e d i b i l i ty gap b e t w e en s c i e n t- i s ts and the g e n e r al p u b l i c. C an you o f f er a q u i ck e x a m p le in the h e r b i c i de a r e a? Just off hand, no. But I think we h a ve s o me p r o- If we s ay that t h e re is no h a z a rd to t h e se m a t e r i a l s, and D r. D e w e y: b l e ms c o m i ng up. F or e x a m p l e, c o m p o u n ds r e q u i r i ng c a r c i n- o g e n ic s t u d i es a re ( m a l e ic h y d r a z i d e) and a m i t r o l e. C o m p o u n ds r e q u i r i ng f u r t h er t e r a t o g e n ic s t u d i es a re 2 , 4 - D, a m i t r o l e, 2 , 4 , 5 , -T and c a c o d y l ic a c i d. C o n s i d er the d i o x i n s. T he U S DA s a ys it n e e ds a d d i t i o n al i n f o r m a t i on on 2 , 4 - D, 2 , 4 - D B, 2 , 4 - D P, ( s e s o n e ), d i c a m b a, t o x a p h e n e, 2 , 4 , 5 - T, t r i c a m b a, e r b on and s i l- v e x. l a t er t h ey a re j u d g ed h a z a r d o u s, we w i ll find o u r s e l v es in a p o s i- tion that is d i f f i c u lt to d e f e n d. We had b e t t er r e c o g n i ze s o me of t h e se f a c ts and be a l i t t le m o re r e a l i s t ic in our a p p r o a c h. We h a ve b e en the e x p e r t s, up to a point, b e c a u se w efve b e en w o r k i ng w i th only one type of a u d i e n c e. T h ey h a ve b e en r e c e p t i ve to us b e c a u se we w e re g i v i ng t h em s o m e t h i ng t h ey n e e d e d. Right or w r o n g, i t 's b e t t er than nothing. But the p u b l ic d o e s n 't quite s ee it t h is w a y. us in s o me of t h e se p r o b l e m s. I think this kind of a p p r o a ch h as a l r e a dy i n v o l v ed in t e r ms of s a f e ty f or e a t i n g. D r. A h r e n s: We had b e en t a l k i ng about the s a f e ty of h e r b i c i d e s, w h en u s ed as d i r e c t e d - - n e v er I d o n 't k n ow of a n y b o dy in the h e r b i c i de f i e ld who h as e v er p r o- m o t ed the c a r e l e ss u se of a h e r b i c i de or s t a t ed that it could be I think we a re in d a n g er in our own thinking if t a k en i n t e r n a l l y. we s ay that j u st b e c a u se a c o m p o u nd is a p o i s o n, or b e c a u se i t 's t e r a t o g e n i c, I don't b e l i e ve that. Y ou h a ve to p r o v e, in the f i r st p l a c e, that it o c c u rs w h e re it m i g ht c a u se i n j u ry w h en I don't think y ou c an t a lk in t e r ms u s ed in a p a r t i c u l ar situation. of the h a z a rd of a c o m p o u nd p er s e. It m u st be r e l a t ed to the u s e. it i s n 't s a f e. D r. D e w e y: I a g r e e, b a s i c a l l y, with what y o u ' re s a y i n g. M a ny t i m es we h a ve f a i l ed to r e c o g n i ze that t h e re a re m i s u s e s, and I think t h is is s o m e t h i ng we h a ve to count on. I a g r ee that m a y be t h e se m a t e r i a ls a r e n 't a h a z a rd w h en p r o p e r ly u s e d. But the p o i nt is that we a re r e a l ly not in a v e ry good p o s i t i on to be m a k- ing this j u d g e m e n t. We had b e t t er l et the e x p e rt in this f i e ld d e- c i de on the l e v el of h a z a r d. In 1 9 5 6 - 1 9 5 7, w h i le s e r v i ng on the N a t i o n al C o m m i t t ee of the E n t o m o l o g i c al S o c i e ty of A m e r i c a, P u b l ic R e l a t i o ns C o m m i t- t e e, we thought that we shouldn!t t a lk about i n s e c t i c i d es as p o i- s o n s. R a t h er we should r e f er to t h em as p e s t i c i d e s, or a n y- thing but p o i s o n o us m a t e r i a l s. t a ke we c o u ld h a ve m a d e. As a r e s u l t, we h a ve p e o p le u s i ng t h e se m a t e r i a ls and thinking t h ey a re s a fe b e c a u se t h ey bought t h em in the s u p e r m a r k e t. I think it w as the b i g g e st m i s- M r. S i m m o n s: W e ' ve l e a r n ed to l i ve with p e s t i c i d es f r om the s t a n d p o i nt of a c u te o r al L.D50. N ow w e ' re l e a r n i ng t h e se things h a ve o t h er e f f e c t s. It i s n 't u n r e a s o n a b le to e x p e ct c h e m i c a ls to h a ve t h e se s i de e f f e c t s, but we s e em to be e v a l u a t i ng t h em f r om a standpoint of a d e s i r a b le and u n d e s i r a b l e, r e g a r d l e ss of r a t e, r a t h er than at a no e f f e ct and an e f f e ct l e v el at a g i v en r a t e. A re we going to m o ve t o w a r ds a d e c i s i on m a k i ng p r o c e d u re u s i ng e f f e c ts at s p e c i f ic r a t es as the g u i d e l i ne in the a c c e p t a n ce of a p e s t i c i d e? It a ll g o es b a ck to the D e l a n ey D r. D e w e y: N ow I think y o u ' re r e a l ly getting into the b a s is f or t he d i f f i c u l ty w e ' re e n c o u n t e r i n g. If any m a t e r i al c a u s es c a r c i n o g e n i c i t y, the D e l a n ey C l a u s e. C l a u se would be u s ed to e l i m i n a te i ts u s e. T he r e s p o n se to a c h e m i c al is dependent on the d o se a d m i n i s t e r e d. e n o u gh t a b le s a l t, or m a ny o t h er h o u s e h o ld i t e m s, you c an c r e a te a ll k i n ds of p r o b l e m s. But the D e l a n ey C l a u se h as not b e en a p- p l i ed a c r o ss the b o a rd with m a ny c h e m i c a l s. At the p r e s e nt t i m e, n e i t h er the p u b l ic n or our l e g i s l a t i ve g r o u ps a re w i l l i ng to a c c e pt the c o n c e pt of d o se r e s p o n se i n f o r m a t i on to m a ke j u d g e- m e n ts on t h i n gs l i ke c a n c e r. If you u se I r e c e n t ly m et with a g r o up of m e d i c al t o x i c o l o g i s ts and t h ey s p e nt t w o - t h i r ds of t h e ir t i me a r g u i ng about the r i d i c u l o us s i t u- a t i on that e x i s ts r e l a t i ve to the D e l a n ey C l a u se and c a n c e r. One of the d i f f i c u l t i es is that our s t a n d a r ds and r u l es h a ve changed. W a rm b l o o d ed p e s t i c i de t o x i c i ty u s ed to be l i m i t ed to r e s i d u es in food or a c u te t o x i c i t y, as you m e n t i o n e d. T o d ay o ur r u l es a re c h a n g i n g. T h ey now i n v o l ve the m o re subtle e f f e c t s, but no one h as e s t a b l i s h ed w h at t h e se s t a n d a r ds a re y e t. Until t h e se stand- a r ds a re e s t a b l i s h e d, i n d u s t ry is up in the a i r, and nobdoy k n o ws w h e re t h e y ' re going or w h at the j u d g e m e n ts a re going to be b a s ed upon. T h is is one r e a s on why I s a y, l e t 's not be caught m a k i ng s t a t e m e n ts out of our a r ea of r e s p o n s i b i l i t y. L e t 's r e c o g n i ze the p e o p le that a re r e s p o n s i b le f or t h e se a r e a s. l e a st D r. White: W e ' re in an u n r e a l i s t ic situation, I think. At an e x t r a o r d i n a ry s i t u a t i on w h e re the e x p e r ts a r e n 't the o n es r e f- e r e e i ng the g a m e. We t a lk as e x p e r ts and we a r e, but who a c- c r e d i ts e x p e r ts and who is our s p o k e s m a n - - o u t s i de of e a ch one of us as an individual. As an i n d i v i d u a l, I am f a c ed with the w h o le s e r i es of e n v i r o n m e n t al o r g a n i z a t i o ns that e x i st in the United S t a t e s. W h e r e 's the s p o k e s m an f or our g r o u p? we p r o c e ed to n a r r ow the c r e d i b i l i ty gap, if you w i l l? We c a n 't go on the w ay we a r e. A n y o ne c an get up and c a ll t h e m s e lf an e x p e r t. I would l i ke y o ur c o m m e n ts on that. How should we p r o c e ed as a g r o up n o w? Should w e, f or i n s t a n c e, be the o n es who a re d r u m m i ng the b o a r ds f or s t a n d a r d s, r a t h er than the p e o p le who a re i n c i t i ng the r i o t, or w h a t? How do I b e l i e ve we a re e x p e r ts in the u se of the m a t e r i al D r. D e w e y: f or the intended p u r p o s e. It b e c o m es a v a i l a b le to us only a f t er it has c l e a r ed c e r t a in h u r d l e s. T he h u r d l es a re c o n s t a n t ly b e- ing c h a n g e d, but nobody k n o ws to what extent. W e ' re s o rt of u n d er a blindfold running down the t r a c k. If w e ' re g o- One thing we should s t r i ve f or is b e t t er s t a n d a r d s. ing to h a ve an E n v i r o n m e n t al P r o t e c t i on A g e n c y, I think it b e- h o o v es u s, t h r o u gh our a g e n c i e s, to t ry to obtain r e c o g n i t i on that m a t t e rs of t h is s o rt should not be s e t t l ed on a p o l i t i c al and e m o t i o n al b a s i s, but should be j u d g ed on f a c t u al b a s i s. s i b l e, we should set up a b u f f e r i ng s y s t em b e t w e en the p o l i t i c al a p p o i n t ee in o f f i ce and the s t a ff t h a t 's doing the the d e c i s i o n. T he p o l i t i c al appointee should be p r o t e c t i ng the t e c h n i c al staff so d e c i s i o ns a re b a s ed on f a ct and c a r e f ul c o n- s i d e r a t i o n. M a ny c o n g r e s s m en won't a g r ee with t h is a p p r o a c h, but I b e l i e ve t h is is p r e s e n t ly one of our p r o b l e m s. If p o s- w o r k, and m a k es A n o t h er thing l a c k i ng in our s y s t e m, and is p r o b a b ly one of the r e a s o ns why w e ' re in t r o u b le w i th 2 , 4 , 5 - T, is that m a ny of the o p e r a t i o ns and s t a n d a r ds w e re set 2 0 - 25 y e a rs ago. T he t e c h- n o l o g y, t e s ts and s t a n d a r ds a re m u ch m o re s t r i ct t o d ay than t h ey w e re at that t i m e. Y e t, we h a ve no b u i l t - in m e c h a n i sm f or r e- e v a l u a t i ng s o me of t h e se m a t e r i a ls to m a ke s u re that t h ey a d- h e re to p r e s e nt d ay s t a n d a r d s. So what h a p p e n s? A ll at o n ce s o m e o ne f i l es a c l a im in c o u r t, p e r h a ps v a l id t o d a y, but 20 y e a rs a g o, b r i n g i ng c h a os to the w h o le a r e a. We m ay n e ed to plug into our s y s t em a m e t h od of r e v i e w i ng and updating our in t h e se a r e a s. F or e x a m p l e, o ur m e t h o ds of a s s a y- s t a n d a r ds ing and d e t e r m i n i ng p o s s i b i l i t i es of c a r c i n o g e n i c i t y, t e r a t o g e n- i c i ty and m u t a g e n i c i ty a re r e l a t i v e ly n e w. T h e re w e re p r a c t i- c a l ly no t e s ts f or t e r a t o g e n i c i ty in I960. We s t i ll do not h a ve a r e f i n e m e nt w h i ch the t o x i c o l o g i s ts a re w i l l i ng to a c c e p t. T h ey a re not in a g r e e m e nt on w h at is a d e q u a t e. i g n o r ed D r. W h i t e: How do we c h a n ge the r u l e s? In m a ny i n s t a n c e s, r e c o g n i t i on of the p r o b l em D r. D e w e y: h a lf the b a t t l e. We a re t r y i ng to w o rk t h r o u gh thp A s s o c i a t i on of L a nd G r a nt C o l l e g e s. I think our a s s o c i a t i o ns and our own a t t i t u d es h a ve to be c h a n g e d, and we h a ve to h a ve s o me u n i s on of a g r e e m e nt in t h is a r ea if we a re going to be e f f e c t i v e. is D r. G r e e n: T he g r e a t e st m i s u s e, in s o me c a s e s, s e e ms to be in c r o ps w h e re i n d u s t ry c a n 't a f f o rd to do the t o x i c o l o gy w o r k; c o n s e q u e n t l y, t h ey r e f u se to d e v e l op c o m p o u n d s. h a ve r e s t r i c t i o n s, or s o m e b o dy is not w a t c h i ng c l o s e l y, t h ey w i ll u se a m a t e r i al that i s n 't r e g i s t e r e d. T he p u b l ic c o n s u m es the p r o d u ct without k n o w i n g. Is it u n r e a s o n a b le to s u g g e st that the f e d e r al g o v e r n m e nt t a ke the r e s p o n s i b i l i ty f or s t a n d a r d i z- ing t o x i c o l o gy s t u d i es and a c t u a l ly do the w o r k, p a r t i c u l a r ly in i m p o r t a n ce c r o ps w h i ch m ay not be of g r e at enough e c o n o m i c al f or i n d u s t ry to go t h r o u gh a ll the p r o c e d u r es n e c e s s a ry f or r eg i s t r a t i o n? If u s e rs don't I a g r ee that t h is is r e a l ly one of the p r o b l e m s. D r. D e w e y: If y ou a re f r om the n o r t h e a st w h e re t h e re is a g r e at d i v e r s i ty of c r o p s, you c an a p p r e c i a te h ow g r e at this p r o b l em is b e c o m i n g. At the p r e s e nt t i me we h a ve a r e g i o n al I R -4 p r o j e c t, w h i ch is a m e a ns s et up at the f e d e r al l e v el f or the p u r p o se of r e g i s t e r- ing m i n or u s es of p e s t i c i d e s. is i n a d e q u a t e. In f a c t, i t 's a l r e a dy i n a d e q u a t e. We h a ve t r i ed to f u r n i sh i n f o r m a t i on at l e v e ls w h e re we thought p r o b l e ms of l e a st c o n s i d e r ed t h is s o rt w o u ld be t a k en into a c c o u n t, or at I think we a re going to find this I n d u s t ry cannot be e x p e c t ed I don't b e l i e ve the p r o b l em of m i n or u s es or and r e c o g n i z e d. m i n or c r o ps is r e c o g n i z ed a d e q u a t e ly at the f e d e r al l e v e l. T he i n d i v i d u al s t a te c e r t a i n ly c a n 't do it. to s p e nd s u ms f or r e g i s t r a t i on w h i ch a re g r e a t er than t h ey a re g o i ng to r e a l i ze in r e t u r n s. E i t h er we m u st c h a n ge our a p p r o a ch or p e r h a ps l e a ve the r e s p o n s i b i l i ty up to the f e d e r al g o v e r n m e n t. P r e s e n t l y, data h as to be d e v e l o p ed f or e a ch c r op M a y be we should be a l i t t le m o re l i b e r al in t h is a r ea and r e g- i s t er u s es on the b a s is of s i m i l ar c r o ps so r e s e a r ch would not h a ve to be d u p l i c a t ed f or e a ch c r o p. e v en h a rd f or our E x p e r i m e nt S t a t i o ns to j u s t i f y; y et the m a t i on m u st c o me f r om s o m e w h e re if we continue to r e q u i re In m a ny i n s t a n c es it is i n d i v i d u a l l y. i n f o r- it. F or e x a m p l e, I r e c e n t ly r e q u e s t ed a D DT l a b el at the f e d e r al l e v el f or s o me u s es w h i ch we r e c o m m e nd in N ew Y o r k. One of t h e se w as f or u se on b l a c k b e r r i es and r a s p b e r r i e s. T h e se c r o ps r e p r e s e nt only 1,200 a c r es in the w h o le s t a t e, and w e ' re only t a l k- ing about a s i n g le a p p l i c a t i o n. T he f e d e r al g o v e r n m e nt w o u ld not a c c e pt t h is b e c a u se the r e s e a r ch w as b a s ed on s t r a w b e r r i e s, but w o u ld a c c e pt a 10,000 a c re u s a ge on f r e sh m a r k et s w e et c o rn f or about 9 a p p l i c a t i o ns at 1 l b / a c r e / a p p l i c a t i o n. T h is s e e ms r i d i c u l- o us to m e! We should spend m o re r e s e a r ch t i me w o r k i ng on s w e et c o rn t r y i ng to find s u i t a b le a l t e r n a t i v e s, r a t h er than w o r k i ng on b l a c k b e r r i es to find a one pound u s a ge i n v o l v i ng a t o t al 1,200 as c o m p a r ed to 90,000 l b s. on s w e et c o r n. T h is is ic that s e e ms to be c o m p l e t e ly o v e r l o o k e d. the kind of l b s ., l o g- D r. D a n i e l: Who do the p r a c t i t i o n e rs u s i ng a g r i c u l t u r al p r o d u c ts h a ve in W a s h i n g t on to r e p r e s e nt t h e m? T h is c a me out v e ry c l e a r ly at the A m e r i c an S e ed T r a de M e e t i n gs in 1970. A lot of p e o p le f e el that, in the D e p a r t m e nt of A g r i c u l t u r e, t h ey h a v e n 't had s o m e o ne to c h a m p i on the p r o d u c e r 's c a u s e. How do we p e r f o r m e r s, p r o d u c e rs and u s e rs r e p r e s e nt o ur golf c o u r se s u p e r i n t e n d e n ts in W a s h i n g t o n, so o ur t u rf is r e a dy f or the c a r ts and the p e o p le who h a ve m o re l e i- s u re t i m e? How do we r e p r e s e nt the h o m e o w n er in W a s h i n g t on so he h as s o m e t h i ng b e s i d es c r a b g r a ss f or the f u t u re l a wn in W a s h i n g- t o n? H ow do we r e p r e s e nt t h e se u s e rs and r e p r e s e nt t h em as a p a rt of good e n v i r o n m e n t? S p e c i al D i s c u s s i on P e r i od ( T he f o l l o w i ng q u e s t i o ns and a n s w e rs w e re v i e w ed f o l l o w i ng a t o ur of O. M. Scott & Sons r e s e a r ch f a c i l i t i e s. Host f or the t o ur w as D a v id G r e e n, S c o t ts P r o d u ct D e v e l o p m e n t .) D r. D a n i e l: How a re you a p p l y i ng l i q u i ds in s m a ll p l o t s? What t y pe of s p r a y er and c a n i s t er do you u s e? M a ny of us n e ed b e t- t er s m a ll plot a p p l i c a t i on t e c h n i q u e s. M r. G r e e n: T he s m a ll plot liquid a p p l i c a t i o ns a re m a de t h r o u gh a m o d i f i ed s p r ay s y s t em that we d e v e l o p ed h e re at S c o t ts ( F i g. 1). We u se an a ir p r e s s u re tank that can be c a r r i ed by the a p p l i c a t or or a t t a c h ed to a b a c k - p a c k, as our s o u r ce of p r e s s u r e. T h is tank is c h a r g ed with 1 2 0 - 1 50 lbs PSI and then, t h r o u gh the u se of a r e g u l a t o r, t h is p r e s s u re is r e d u c ed to 30 lbs PSI. Figure 1. M o d i f i ed spray system developed for making small plot liquid a p p l i c a t i o n s. T he a c t u al s p r ay unit c o n s i s ts of t wo v a l v e s; one t u r ns the a ir p r e s s u re on and off, w h i le the o t h er r e g u l a t es the s p r ay ( F i g. 2) T he c o n t a i n er f or the s p r ay c o n s i s ts of a p l a s t ic N a l g e ne bottle w i th a s l e e ve that s l i d es o v er the bottle and p r o v i d es additional s u p p o rt to the s i d es and bottom. T he a ir p r e s s u re is t u r n ed on o n ce to c h a r ge the c o n t a i n e r, then a ir p r e s s u re is t u r n ed off. T he a s s e m b ly is i n v e r t ed so the liquid is in the d i s c h a r ge side of the c o n t a i n e r, then the liquid v a l ve is opened to d i s c h a r ge the a c t u al s p r a y. We h a ve a d a p t e rs m a de to u t i l i ze 4 o z ., 8 oz. and 1 l i t er N a l g e ne b o t t l e s. Figure 2. Close-up of spray unit and container b o t t le with s l e e v e ). ( p l a s t ic Nalgene A f t er t h r ee y e a rs of u s e, we h a ve found that this s y s t em v e ry e f f e c t i v e, d u r a b le and c o m p l e t e ly p o r t a b l e. T he N a l g e ne b o t t l es u s ed in a p p l i c a t i on a re d i s c a r d ed a f t er the t r e a t m e n t. T h is g r e a t ly r e d u c es the p o s s i b i l i ty of c o n t a m i n a t i on in our p l o t s. One p r o b l em we h a ve e n c o u n t e r ed is that o c c a s i o n a l ly we get a N a l g e ne bottle that w i ll not w i t h s t a nd the t h i r ty pounds of a ir p r e s s u r e, or is i m p e r f e ct in i ts s e al to the s p r ay head. is By holding the s p r ay unit u p r i g h t, w h en the c o n t a i n er is c h a r g e d, any d e f e c ts w i ll be noted b e f o re the m a t e r i al is d i s c h a r g e d, and the a p p r o p r i a te c o r r e c t i on a c t i on can be taken. D r. W a r d: A f t er s p r a y i ng a c h e m i c a l, do y ou f l u sh y o ur line with w a t e r? M r. G r e e n: We do not f l u sh or p u r ge the s y s t em with w a t e r. C o n- c e rn by s o me of our p e o p le h as b e en shown, but we h a ve not e n- c o u n t e r ed any p r o b l e ms in r e g a rd to c o m p o u nd c o n t a m i n a t i o n. addition to d i s c a r d i ng the c o n t a i n e r, the s y s t em is a l so p u r g ed with a ir a f t er the liquid is d i s p e n s e d. In it is a c a n i s t e r. T he plug is an i n t e g r al p a rt of M r. T u r g e o n: We h a ve a s i m i l ar s y s t em at M i c h i g an State. We u se a one l i t er p l a s t ic N a l g e ne bottle and, r a t h er than a s l e e ve a r r a n g e m e n t, the lid of t h is c a n i s t er that o p e r a t es off a C O2 p r e s s u re s o u r c e. A ll of t h is is c a r r i ed on a a r o u nd the i n d i v i d u al that is s p r a y i n g. As f ar as the d i s c h a r ge p r o b l em is c o n c e r n e d, we t e s t ed t h is s y s t em with 2 , 4 -D e s t er and, u s i ng t o m a to plants as the t a r g et plant, we found that with n o r m al d i s c h a r ge of C O2 t h r o u gh the s y s t e m, t h e re w as no s u b- sequent c a r ry o v er of the h e r b i c i d e. So our s y s t em is quite w e ll p u r g ed with the CC>2. in the u p s i de down p o s i t i on belt D r. B i n g h a m: into the ground w a t er u s i ng y o ur s p r i n k l i ng s y s t e m. A re y ou studying the w ay the h e r b i c i d es get into s u r f a ce w a t e r? I w as quite i n t e r e s t ed in the h e r b i c i d es that get M r. G r e e n: We h a ve the c a p a b i l i ty to c o l l e ct both s u r f a ce and s u b - s u r f a ce w a t er f r om t h e se t e st p l o t s. T he p l o ts a re d i v i d ed by c e m e nt d i v i d e rs a p p r o x i m a t e ly 4 ft. in depth and the s u r f a ce of the plot a r ea w as g r a d ed to a 4% s l o p e. T he s u r f a ce c o l l e c- tion is done by a t i le w h i ch r i s es to the s u r f a ce on the l ow s i de of e a ch plot and d r a i ns into the c o l l e c t i on b a s i n. S u b - s u r f a ce c o l l e c t i on is done f r om a 4 in. c l ay t i le c e n t e r ed in e a ch of the p l o t s. c a t i on w as p e r f o r m ed in the a r e a. T he c o r r e ct s u r f a ce p r e p a r- ation w as m a d e, and the sod w as p l a c ed on the s u r f a ce of the n a t i ve s o i l. It a l so d r a i ns into the c o l l e c t i on b a s i n. No s o il m o d i f i- D r. K a u f m a n: A re y ou looking f or d e g r a d a t i on p r o d u c t s, p a r e nt m a t e r i al or both? M r. G r e e n: We a re looking p r i m a r i ly at the p a r e nt m a t e r i a l. In s o me c a s e s, we a re looking f or b r e a k d o wn p r o d u c ts as w e l l. We a re looking not only f or p e s t i c i d e s, but we a re a l so c o n c e r n ed about the m o v e m e nt of the p h o s p h o r us and n i t r o g en and how t h e ir a v a i l a b i l i ty or s o l u b i l i ty is r e f l e c t ed on t h e ir m o v e m e nt in the s u r f a ce and s u b - s u r f a ce w a t e r s. D r. B i n g h a m: How do you s a m p le the w a t er that c o m es o f f? Do you s a m p le at i n t e r v a l s, or a c c o r d i ng to v o l u m es of w a t er that y ou c o l l e c t? s a m p l es f r om the w a t er s a m- M r. G r e e n: P r i m a r i l y, we c o l l e ct p le f a c i l i ty at s p e c i f ic i n t e r v a ls - - n ot on a v o l u me b a s i s. Our c o l l e c t i on f a c i l i ty is s u ch that we c an c o l l e ct only up to a c e r t a in v o l u me at any one t i m e. T he e x c e ss is p e r m i t t ed to o v e r f l o w. We a re o p e r a t i ng s t r i c t ly on t i me i n t e r v al a r ea a f t er r a i n f a l l, or a f t er i r r i g a t i on h as t a k en p l a ce on the t u r f. T wo b a s ic a p p r o a c h es a re u s ed to d e t e r m i ne the content of In s o me c a s es t h e se w a t e r s: b i o - a s s a ys and c h e m i c al a s s a y s. we a re running s a m p l es by both m e t h o ds in an a t t e m pt to c o r r e- l a te r e s u l t s. a f t er t r e a t m e nt of the D r. A p p l e b y: How do you apply y o ur g r a n u l ar f o r m u l a t i o ns t h e se s m a ll p l o t s? to M r. G r e e n: T h e se a p p l i c a t i o ns a re m a de t h r o u gh the u se of m o d- i f i ed S c o t ts s p r e a d e r s. We cut the ends off a s t a n d a rd s p r e a d e r, r e m o v ed a s e c t i o n, then r e p l a c ed the ends at a n a r r o w er width. T he S c o t ts s p r e a d er s i z es a v a i l a b le c o m m e r c i a l ly a re 18 in., 24 in. and 36 in. H e re we h a ve cut t h em down to as n a r r ow as an 8 in. width, and we h a ve s o me o t h er odd widths a v a i l a b l e. O t h er t h an t h is s h o r t e n i ng o p e r a t i on of the s p r e a d e r, we u se e x a c t ly the s a me c o m m e r c i al s p r e a d er that a h o m e o w n er or p r o f e s s i o n al p e r s on would u t i l i ze in a p p l i c a t i on of a p r o d u c t. D r. H e m p h i l l: A re you able to d e t e r m i ne the content of the w a- t er f r om the d r a i n a ge and m o b i l i ty p l o ts d i r e c t l y, or m u st you c o n c e n t r a te by a c t i v a t ed c a r b on or s o me o t h er m e t h o d? M r. G r e e n: At the p r e s e nt t i me we a re running our a n a l y s is w o rk on the s t r a i g ht c o l l e c t ed s a m p l e. We a re not c o n c e n t r a- ting it. T h is d r a i n a ge and m o b i l i ty f a c i l i ty is a r e l a t i v e ly n ew s y s t e m, and we a re s t i ll in our i n f a n cy as f ar as d e v e l o p i ng t e s t i ng p r o c e d u r es and a ll of our t e c h n i q u e s. D r. G r e e n: How do you c o me up with f e r t i l i z er r e c o m m e n d a- t i o ns f or the h o m e o w n e r, b a s ed on y o ur f e r t i l i ty r e s u l ts h e re on the s t a t i o n? to o t h er s o i ls and o t h er e n v i r o n m e n t al c o n d i t i o n s? In o t h er w o r d s, how do you e x t r a p o l a te r e s u l ts of M r. G r e e n: We h a ve f i e ld s t a t i o ns l o c a t ed in o t h er a r e as the c o u n t r y, u t i l i z i ng d i f f e r e nt s o il t y p es and c l i m a t ic c o n d i- t i o n s. Our f i e ld s t a t i on in T e x as w as m o v ed r e c e n t ly in o r d er to obtain a d i f f e r e nt s o il t y p e. T he s t a t i on w as l o c a t ed on a h e a vy c l ay s o i l, and we h a ve now m o v ed it to an a r ea that is a l m o st c o m p l e t e ly sand. In addition to the w o rk at our f i e ld s t a t i o n s, we a l so p e r f o rm a c o n s i d e r a b le amount of t e s t i ng on h o me l a w ns a c r o ss the c o u n t r y. A s e p a r a te d i v i s i on h e re at S c o t ts t a k es the p r o p o s ed p r o d u ct f r om the p r o d u ct d e v e l o p- m e nt g r o up and d i s p e r s es it a c r o ss the c o u n t ry in v i r t u a l ly e v e ry s t a te w h e re the p r o d u ct would be c o n s i d e r ed f or s a l e. By t h is s t a ge in d e v e l o p m e n t, the p r o d u ct n e ed no l o n g er be a p p l i ed by p r o f e s s i o n a l s, but is a c t u a l ly g i v en to the h o m e o w n er who h as a s p e c i f ic l a wn p r o b l em that the p r o d u ct is d e s i g n ed to c o n t r o l. T he h o m e o w n er m a k es the a p p l i c a t i on of the p r o d u ct h i m s e l f. In o t h er w o r d s, h o m e o w n e rs t e ll us w h i ch p r o d u ct is m o st d e- s i r a b le to t h e m. N o r m a l l y, we w i ll h a ve t wo or t h r ee f o r m u- l a t i o ns that h a ve shown c o n s i d e r a b le p r o m i se in the d e v e l o p m e nt s t a ge and the h o m e o w n e rs a re i n s t r u m e n t al in m a k i ng the f i n al d e c i s i on on the p r o d u ct in q u e s t i o n. A f t er the c o n s u m er d i v i- s i on has obtained the h o m e o w n e r s' opinion of the p r o d u c t s, we d e t e r m i ne if ( 1) we c an s e ll the p r o d u ct f or a p r o f it and (2) the m a r k et a r ea is of s u f f i c i e nt s i ze to w a r r a nt our i n v e s t m e nt in the p r o d u c t. t i on h a ve b e en d e t e r m i n i ng f a c t o rs in the d e v e l o p m e nt of c o n- s u m er p r o d u c t s. In r e c e nt y e a r s, p r o d u ct v a r i a t i on and r e g i o n a l i z a- D r. S y l v e s t e r: What p r e - e m e r g e n ce c r a b g r a ss k i l l e rs h a ve g i v en y ou the b e st r e s u l t s? M r. G r e e n: We h a ve t wo m a t e r i a ls that we i n c l u de in our t e s ts h e re in M a r y s v i l le as s t a n d a r d s: b e n s u l i de and D a c t h al ( D C P A ). t h ey h a ve b e en v e ry good in the p a st as f ar as p r o v i d i ng e x c e l- lent p r e - e m e r g e n ce c r a b g r a ss c o n t r o l. T h e re a re o t h er m a t e r- i a ls on the m a r k e t, of c o u r s e, but I w o u ld h a ve to point to t h e se t wo as being the m o st outstanding in p r o v i d i ng p r e - e m e r g e n ce c r a b g r a ss c o n t r ol f r om a s i n g le a p p l i c a t i o n. M r. B a n g s: T h e re a re s e v e r al e f f e c t i ve p r e - e m e r g e n ce c r a b- g r a ss c o n t r o ls that a r e n 't u s ed in our p r o d u ct line. Would y ou point out the r e a s o ns f or t h i s? M r. G r e e n: S e v e r al f a c t o rs a re c o n s i d e r ed b e f o re we d e c i de to i n c o r p o r a te a s p e c i f ic c h e m i c al into our p r o d u ct line. and m o st i m p o r t a n t, the c h e m i c al m u st be s a f e. S c o t ts h as a c o m m i t m e nt to not m a r k et any p r o d u ct w h i c h, in r e c o m m e n d ed u s a g e, m i g ht be a h e a l th h a z a rd to the u s e r, his f a m i ly or his p e t s. F i r s t, A l s o, we look f or c h e m i c a ls that c an be u s ed on m a ny t y p es of t u r f g r a s s. F or e x a m p l e, b e n s u l i de and D a c t h al a re both e f f e c- t i ve in c o n t r o l l i ng c r a b g r a ss w h en a p p l i ed as p r e - e m e r g e n ce h e r b i c i d e s. T he i m p o r t a nt thing h e re is that one p o s s e s s es c o n s i d e r a b ly m o re t o l e r a n ce to a b r o a d er r a n ge of t u r f g r a s s e s. B e n s u l i de is s a fe f or u se on b l u e g r a s s e s, b e n t g r a s s es and both c o a r se and f i ne f e s c u e s. D a c t h a l, on the o t h er hand, cannot be u s ed on b e n t g r a ss without s e r i o us i n j u r y, n or c an it be u s ed w i th f i ne f e s c u es without s o me thinning t a k i ng p l a c e. If we c an u se one c o m p o u nd o v er a w i de g e o g r a p h ic a r ea f or m a ny d i f f e r e nt t y p es of t u r f g r a s s e s, as c o m p a r ed to another w h i ch c an be u s ed in a s m a l l er g e o g r a p h ic a r ea and m a y be only on one or t wo d e s i r a b le t u r f g r a s s e s, we would m o st c e r t a i n ly g i ve a d d i t i o n al c o n s i d e r a t i on to the h e r b i c i de w h i ch s h o ws the g r e a t e st d e g r ee of t u rf t o l e r a n c e. T h e se a re s o me of the f a c t o rs we t a ke into c o n s i d e r a t i on b e f o re we m a ke a f i n al d e c i s i on in r e- g a rd to a p r o d u ct a c t i ve i n g r e d i e nt that w i ll be sold c o m m e r c i a l- ly to the h o m e o w n e r. M I D W E ST C U R R E NT T R E N DS IN T U R F G R A SS W E ED C O N T R OL W i l l i am H. D a n i el D e p a r t m e nt of A g r o n o my P u r d ue U n i v e r s i ty L a f a y e t t e, Indiana 47907 Introduction T he d e v e l o p m e nt of m o d e rn h e r b i c i d es u s ed f or t u rf c o n t r ol h as p r o v i d ed s a f e, e f f i c i e nt and e f f e c t i ve t u rf m a n a g e m e nt t o o l s. T h e se t o o ls a re good, but it is w e ll e s t a b l i s h ed that a b e t t er u n- d e r s t a n d i ng of the i n t e r a c t i on of h e r b i c i d es with e n v i r o n m e n t al f a c t o rs m u st be obtained. Solving w e ed p r o b l e ms t o d ay r e q u i r es t o t al p e r f o r m a n c e; s e l e c t i ve c o n t r ol of u n w a n t ed v e g e t a t i on without c o n t a m i n a t i ng the e n v i r o n m e n t. i n d i s c r i m i n a t e ly A m e r i ca w as not m a de g r e at by a d o - w i t h o ut attitude, and as t u rf r e s e a r c h e r s, we m u st not be h e m m ed in unduly in o ur r e- s e a r ch p r o g r a m. T he c u r r e nt t r e nd in t u r f g r a ss w e ed c o n t r ol d e m a n ds an i n c r e a s ed u s e a ge of h e r b i c i d e s. T h u s, m o re k n o w- l e d ge on h e r b i c i d al a c t i o n, a m p le e d u c a t i o n al p r o g r a ms and a d e- q u a t e, but f a i r, p e s t i c i de l a b e l i ng is e m m i n e n t ly n e e d e d. T he p r e s e nt t r e nd in w e ed c o n t r ol in the M i d - W e st is b a s ed on continuous r e s e a r ch and c an be b e st i l l u s t r a t ed by p r e s e n t i ng the h i s t o ry of t u rf h e r b i c i d al d e v e l o p m e n t. B r o a d l e af W e e ds 2 , 4 -D 2 , 4 -D w as u s ed f or the f i r st t i me in Indiana in 1945 at the E l ks C o u n t ry C l ub n e ar L a f a y e t t e. S i n ce that t i me we h a ve u s ed the s o d i um s a l t s, the high v o l a t i le e s t e r s, the l ow v o l a t i le e s t e rs and the a m i ne s a l t s. T he lithate f o rm has not r e c e i v ed w i de a t- tention. Within the 25 y e a rs of c o m m e r c i al u s e, 2 , 4 -D has r e- c o r d ed a p h e n o m e n al r e c o rd of t o l e r a n c e, a c c e p t a n c e, u se and s u c c e s s. T he c u r r e nt t r e nd f or 2 , 4 -D c o n t i n u es to be the adding of o t h er m a t e r i a ls to it in o r d er to h a ve b r o ad s e l e c t i v i t y, plus e n h a n c e m e nt b e t w e en c h e m i c a l s. 2 , 4 , 5 -T 2 , 4 , 5 -T g o es b a ck to about 1950, or p e r h a ps e a r l i e r. Its s e- l e c t i v i ty opened n ew a v e n u es f or c o n t r o l l i ng v i n ey w e e d s, p a r t i- c u l a r ly c l o v e r, at r a t es that w e re quite a c c e p t a b l e. 2 , 4 -D with 2 , 4 , 5 -T g a ve a c o m b i n a t i on f or b u sh k i l l i ng w h i ch h as b e en v e ry u s e f u l, h o w e v e r, i ts c u r r e nt r e s t r i c t i on f or u se around h o m es and s t r e a ms is q u e s t i o n ed by m a n y. R e p l a c e m e nt by M C PP and d i c a m ba has r e d u c ed h o m e o w n er n e e ds f or 2,4, 5 - T. c a s e s, 2 , 4 , 5 -T did not k i ll c h i c k w e ed or k n o t w e e d. In m o st M C PP A l t h o u gh w i d e ly t e s t ed in E u r o pe and C a n a d a, M C PP h as It is v e ry s e l e c- not r e c e i v ed b r o ad u s a ge in the United S t a t e s. t i ve on c l o v er and c an be added to o t h er m a t e r i a l s. T he u se of M C PP and d i c a m ba s t a r t ed about the s a me t i me in the M i d w e s t. M C PP is p r e s e n t ly u s ed in s o me f o r m u l a t i o n s. D i c a m ba D i c a m ba h as b e en a r e al b o o st to c o m p l e te w e ed c o n t r o l. Its e x c e l l e nt c o n t r ol of k n o t w e ed (at any s t a g e ), c l o v er and c o m- m on c h i c k w e ed h as g i v en us c o m b i n a t i o n s, i n c l u d i ng 2 , 4 -D and d i c a m b a. T h e re is a q u e s t i o n, h o w e v e r, of how m u ch d i c a m ba should be u s e d - - l /8 to l /4 lb. a c t i ve p er a c r e - - to s a t i s f a c t o r i ly do the job. F o r m u l a t i o ns c a r r y i ng 4 to 10 p a r ts 2 , 4 -D to one p a rt d i- c a m ba h a ve b e en f o r m u l a t ed and a re on the m a r k e t. O ur r e- s e a r ch continues t o w a r ds u s i ng the l e a st d i c a m ba p o s s i b le in c o m b i n a t i o ns f or s e l e c t i ve w e ed c o n t r o l. W e e dy G r a s s es P h e n yl m e r c u ry a c e t a t es P h e n yl m e r c u ry a c e t a t e s, s u ch as P M A S, L i q u i p h en and D i- m e t, w e re d e v e l o p ed in the late 1940fs. T h e ir f u n g i c i d al v a l u e, plus t h e ir s e l e c t i ve k i ll of s o me w e e dy g r a s s e s, m a de t h em e x- t r e m e ly p o p u l a r. T he t o x i c i ty of the s o l u t i on to hands ( s k in b u r n s) w as r e p e a t e d ly e x p e r i e n c ed by c a r e l e ss o p e r a t o r s. N e v e r- t h e l e s s, P MA w as the f i r st b r i g ht spot in s e l e c t i ve c r a b g r a ss c o n- t r o l. S e v e r al golf g r e e ns b e c a me f r ee of c r a b g r a ss f or the f i r st t i me in the e a r ly 19 50's with 3 to 5 a p p l i c a t i o ns of P M A. L a t e r, other m a t e r i a ls n e g a t ed it to m i n or u s a g e. It s t i ll c an s e r v e, but the n u m b er of f o r m u l a t i o ns on the m a r k et h as d e c r e a s ed to v e ry f e w. D i - s o d i um m e t h yl a r s o n a te In the l a te s u m m er of 19 53, two plots at P u r d ue U n i v e r s i ty w e re t r e a t ed with m e t h yl a r s o n a t e. M e t h yl a r s o n a t es w e re found to be s u c c e s s f ul in s e l e c t i v i ty c o n t r o l l i ng c r a b g r a s s, then d a l l i s- g r a s s, and l a t er j o h n s o n g r a s s, s e d g e, s a n d b u r s, f o x t a i ls and b a r n- y a r d g r a ss f r om e s t a b l i s h ed t u rf a r e a s. Its l a t er u s a ge f or d a l l i s- g r a ss and j o h n s o n g r a ss c o n t r ol in s o u t h e rn a r e as adds to its s u c- c e s s. T he m e t h yl a r s o n a t e s - - d i - s o d i u m, m o n o s o d i u m, a m i n e -- soon r e p l a c ed the p h e n yl m e r c u r i es f or c r a b g r a ss p r e v e n t i o n. In 1958, p o s t - e m e r g e n ce w as 99% of the c r a b g r a ss c o n t r ol m a r- k e t; t o d ay it is l e ss t h an 5%. M e a n w h i l e, e n t i re golf c o u r s es and m a ny l a w ns h a ve b e en c l e a r ed of g r o w i ng c r a b g r a s s. T he p h i l o- sophy of being a b le to h a ve t u rf without c r a b g r a ss h as p e r m i t t ed the h o m e o w n er to r a i se his s i g h t s, to i n c r e a se his f e r t i l i z e r, to u p g r a de his v a r i e t i e s, and to e x p e ct m o re p e r f o r m a n ce and a c h i e v e m e n t. P o s t - e m e r g e n ce h as b e en l a r g e ly r e p l a c ed p r e - e m e r g e n c e. Why fight the c o m p e t i t i on l a t er w h en it c an be p r e v e n t ed e a r l i e r? N e v e r t h e l e s s ,, the s i g n i f i c a nt c o n t r i b u t i on of c r a b g r a ss k i l l i ng c h e m i c a ls h as b e en i m m e a s u r a b le in l a wn i m p r o v e m e nt in the 20 y e a r s. l a st C r a b g r a ss P r e - e m e r ge O ur p r e - e m e r ge r e s e a r ch b e g an at P u r d ue in 19 54. T h at s a me y e ar a one bag t r e a t m e nt of P AX at K a n s as State U n i v e r- s i ty p r o v ed to be b e n e f i c i a l. By 19 56, our F i e ld D ay f e a t u r ed c r a b g r a ss c o n t r o l s, including A l a n a p, c a l c i um a r s o n a te and l e ad a r s e n a t e. At that t i m e, a r s e n ic p o w d e rs w e re d u s ty and d i f f i c u lt to a p p ly u n i f o r m l y. T he p r i n c i p l e, h o w e v e r, w as p r o v en in the g r e e n h o u se that p h o s p h o r us r e d u c t i on and a r s e n ic b u i l d - up g a ve s e l e c t i ve t o x i c i ty to n u m e r o us p l a n t s, i n c l u d i ng c r a b g r a s s. By 1961, t h e re w e re s e v e r al p r e - e m e r g e n ce c r a b g r a ss c o n t r o ls on the m a r k e t. L o n g - t e rm r e s i d u al f r om c a l c i um a r s o n a te a p p l i ed eight in y e a rs p r e v i o u s ly w as o b s e r v ed in St. L o u i s; s u b s e q u e n t l y, n u m e r o us p l a c es m a ny f o r m u l a t i o ns of a r s e n i c a ls h a ve b e en u s e d. A f t er t h i r t e en y e a r s, o n e - h a lf of my f r o nt l a wn (5,000 sq ft) r e m a i ns c r a b g r a s s - f r e e, w h e r e as the o t h er o n e - h a lf continues y e ar a f t er y e ar to h a ve s o me i n f e s t a t i o n. P oa annua T he b l a ck s h e ep of the t u rf f a m i ly t o d ay is no l o n g er c r a b- g r a s s, but P oa annua, p a r t i c u l a r ly f or the sod g r o w e r, on the f a i r w ay and on the g r e e n. O ur i n i t i al w o rk to find a c o n t r ol f or P oa annua b e g an in 19 50. We h a ve continued to w o rk t h r o u gh n u m e r o us c y c l e s. A r s e n i c, although it f a d es a w a y, d o es c o n t r ol P oa annua. W h en the a r ea is 9 5% P oa annua, it is going to be v e ry n o t i c e- a b le w h en that m u ch g r a ss d i es - w h e t h er it be a f a i r w a y, edge of a g r e e n, or p a r ts of f a i r w a y s. When the a r s e n ic e l i m i n a t es t he P oa annua, t h e re is going to be b a re ground and the n e ed f or r e p l a c e m e n t. T h e r e f o r e, if it is a golf c o u r se not yet t r e a t ed w i th a r s e n i c a l s, t i on in p h o s p h o r u s, a c c u m u l a t i on of a r s e n ic and the and i n c r e a se of d e s i r ed s p e c i e s. it a p p e a rs to be a two y e ar j ob i n v o l v i ng r e d u c- i n t r o d u c t i on O c c a s i o n a l ly t h e re h as b e en d a m a g e, u s u a l ly d e l a y e d, on g r e e ns and f a i r w a y s; e v en l a w n s. But t h is h as b e en the e x c e p- t i on r a t h er than the r u l e. M e a n w h i l e, t i m e ly a p p l i c a t i on and u n i f o rm r a t es h a ve g r e a t ly r e d u c ed the p o t e n t i al of c o m p e t i t i o n. At M a k e t a w ah County C l ub in C i n c i n n a t i, Ohio, the f a i r w ay w as t r e a t ed with a r s e n i c a l s, and e v e n t u a l ly it w as p e r f e ct b l u e- g r a s s. T h ey c h a n g ed s u p e r i n t e n d e n ts and the n ew one added p h o s p h o r us and s t o p p ed the a r s e n i c, and the f a i r w ay is a g a in 9 5% P oa annua. T he p h o s p h o r us additions o v e r r o de the a r s e n i c. It is e s t i m a t ed that o v er 500 golf c o u r s es in the M i d w e st p r o g r a ms with a r s e n i c a l s, and N o r t h e a st h a ve f a i r w ay t r e a t m e nt and o v er 100 of t h e se h a ve c o m p l e te P oa annua r e s t r i c t i on as an o n - g o i ng f a i r w ay p r o g r a m. should be an e a s i er w a y. It is d i f f i c u lt and t e d i o u s. T h e re T he v a l ue of o t h er p r e - e m e r g e n ce m a t e r i a l s, beyond a r s e n- i c a l s, o f f er c e r t a in c o n v e n i e n c e. In 19 64, T u p e r s an w as w i d e ly r e s e a r c h ed and it has s e r v ed on n ew s e e d i n gs v e ry w e l l. B a l an at 3 l b s. a c t i ve p er a c re h as p r e v e n t ed c r a b g r a ss g e r m i n a t i o n. So w i ll D a c t h al and B e t a s an at the p r o p er r a t e. On e s t a b l i s h e d, u n i f o rm t u r f, one e a r ly f a ll a p p l i c a t i on m ay be s a t i s f a c t o ry f or P oa annua c o n t r o l. T h e re is m u ch p o t e n t i al in the u se of g r o w th r e g u l a t o r s, s u ch as P o - S a n, to p r o d u ce s h o r t - t e rm r e s t r i c t i on in c l i p p i n g s, etc. T h e re is a l so m u ch p o t e n t i al in c o m b i n a t i o ns w h i ch would p e r m it s e l e c t i ve r e s t r i c t i on d u r i ng i n t r o d u c t i on of s p e c i al n ew v a r i e t i e s, s u ch as e l i te t y pe b l u e g r a s s e s. S u m m a ry With the a v a i l a b i l i t y, s e l e c t i v i ty and p r o g r a ms of h e r b i c i d al f or u s e, n e a r ly e v e ry t u rf w e ed m ay now be c o n t r o l l e d. C o n t r o ls b e n t g r a ss in b l u e g r a s s, f or q u a c k g r a ss in b l u e g r a s s, and t a ll f e s c ue in b l u e g r a ss a re s t i ll n e e d e d. T h e se a re d i f f i c u lt p r o b l e m s. T o d ay it is w i se u s a ge of c h e m i c a ls that should be pushed. A nd it is c a r e f ul planning and m a x i m um u t i l i z a t i on that should be e n c o u r a g e d. N O R T H E RN C U R R E NT T R E N DS IN T U R F G R A SS W E ED C O N T R OL C l a y t on M. S w i t z e r, C h a i r m an D e p a r t m e nt of B o t a ny O n t a r io A g r i c u l t u r al C o l l e ge U n i v e r s i ty of G u e l ph G u e l p h, O n t a r i o, C a n a da I n t r o d u c t i on C h e m i c al w e ed c o n t r ol in t u rf b e c a me f e a s i b le w h en 2 , 4 -D b e c a me a v a i l a b le in 1946. S i n ce that t i m e, m a ny o t h er h e r b i c i d es h a ve b e en d e v e l o p ed f or u se on l a w n s, golf a r e as of t u r f g r a s s. S o me of t h e se p r o v ed h e l p f ul f or a t i m e, but h a ve b e en r e p l a c ed by n e w er and b e t t er m a t e r i a l s. T he p u r p o se of this p a p er is to c o n s i d er o ur p r e s e nt t u r f g r a ss w e ed c o n t r ol m e t h o ds and to d i s c u ss p o s s i b le f u t u re c h a n g es that m ay o c c ur as the r e s u lt of r e s e a r ch a n d / or g o v e r n m e nt and public p r e s- s u r e s. c o u r s es and o t h er At the o u t s e t, it m i g ht be u s e f ul to outline the t u r f g r a ss and w e e ds w i th w h i ch we in e a s t e rn C a n a da and the n o r t h e a s t e rn U n i t ed S t a t es a re c o n c e r n e d. M o st l a w ns and golf c o u r s es in the a r ea c o n t a in p r i m a r i ly b l u e g r a s s es and f e s c u e s. M e r i on and c o m m on K e n t u c ky b l u e g r a ss a re u s ed m o st w i d e ly with F y l k i ng and W i n d s o r, c o m i ng in s t r o n g ly in s o me a r e a s. T h e se t wo g r a s s es a re showing up on m a ny golf c o u r s e s, p a r t i c u l a r ly on t e e s, a p r o ns and a p p r o a c h e s. P e n n l a wn c r e e p i ng r ed f e s c ue is w i d e ly d i s t r i b u t e d, both on l a w ns and on golf c o u r s e s. l a t t er On golf c o u r se g r e e ns one f i n ds T o r o n t o, C - 15 and P e n n- c r o ss b e n t g r a ss u s ed m o st f r e q u e n t l y. N o r t h l a nd and C o h a n s ey l o ok v e ry good in r e s e a r ch t r i a ls in C a n a da b e c a u se of t h e ir e a r ly s p r i ng g r o w t h. T he b r o a d l e af w e e ds found in t u rf in o ur a r ea i n c l u de d a n- d e l i on ( T a r a x a c um o f f i c i n a le W e b e r . ), c o m m on p l a n t a in ( P l a n t- a go m a j or L . ), r i b g r a ss ( P l a n t a go l a n c e o l a ta L . ), h e a l - a ll ( P r u n e l la v u l g a r is L . ), c r e e p i ng c h a r l ie ( G l e c o ma h e d e r a c ea L . ), b l a ck m e d i ck ( M e d i c a go lupulina L . ), m o u s e - e ar c h i c k w e ed ( C e r a s t i um v u l g a t um L . ), V e r o n i ca spp., c r e e p i ng b u t t e r c up ( R a n u n c u l us r e p e ns L . ), E n g l i sh d a i sy ( B e l l is p e r e n n is L.) p l us s e v e r al o t h er l e ss f r e q u e n t ly o c c u r i ng s p e c i e s. W e e dy g r a s s es i n c l u de c r a b g r a ss ( D i g i t a r ia spp.), annual b l u e g r a ss ( P oa annua L#), q u a c k g r a ss ( A g r o p y r on r e p e ns L. B e a u v .) and c r e e p i ng b e n t g r a ss ( A g r o s t is s t o l o n i f e ra L».). Of l e s s er p a n i c u m, and p e r e n n i a l s, s u ch as o r c h a r d g r a ss and t i m o t h y. i m p o r t a n ce a re o t h er a n n u al g r a s s e s, s u ch as f o x t a il and B r o a d l e af W e ed C o n t r ol T he u se of s i n g le h e r b i c i d e s, s u ch as 2 , 4 - D, 2 , 4 , 5 -T or f e n o p r op ( 2 , 4 , 5 - T P ), h as b e en a l m o st c o m p l e t ly r e p l a c ed by m i x t u r es of c h e m i c a l s. S i n ce e a ch h e r b i c i de m i s s es s o me of the w e e ds c o m m o n ly found in t u r f, m i x t u r es o b v i o u s ly would be e x p e c t ed to g i ve a b r o a d er s p e c t r um of c o n t r o l. M a ny m i x- t u r es a re a v a i l a b l e, w i th the m o st c o m m o n ly u s ed o n es being 2 , 4 -D - f e n o p r op ( 2 , 4 , 5 - T P ), 2 , 4 - D - m e c o p r op ( M C P P ), 2 , 4 - D- d i c a m b a, and 2 , 4 - D - m e c o p r o p - d i c a m b a. E v en t h e se m i x t u r es w i ll not c o n t r ol a ll b r o a d l e af w e e ds found in l a w ns in o ur g e o- g r a p h ic a r e a. Y a r r ow ( A c h i l l ea m i l l e f o l i um L . ), s p e e d w e ll ( V e r o n i ca f i l i f o r m is Sm.) and m a l l ow ( M a l va n e g l e c ta W a l l r .) a re a m o ng the m o st c o m m on r e s i s t a nt s p e c i es found. H o w- e v e r, c o n t r ol of s u ch s p e c i es m ay be obtained by u s i ng good m a i n t e n a n ce p r o c e d u r e s - - f e r t i l i z a t i o n, m o w i ng and w a t e r i n g -- in a d d i t i on to the u se of h e r b i c i d e s. T he q u e s t i on a r i s es as to the long r a n ge e f f e c ts of continued u se of t h e se h e r b i c i d es on the d e s i r a b le g r a s s e s. R e m a r k a b l y, f ew s t u d i es of f i ve y e a rs or l o n g er h a ve b e en c a r r i ed out on s p e- c i f ic t u rf s p e c i e s, e v en with 2 , 4 - D. O ur g e n e r al o b s e r v a t i o ns w o u ld i n d i c a te that the p h e n o xy h e r b i c i d es h a ve had no h a r m f ul e f f e c t s, e i t h er d i r e c t ly on the g r a s s, or i n d i r e c t ly by a f f e c t i ng the s o il m i c r o f l o r a. T he s a me s e e ms to be t r ue f or d i c a m b a. N e v e r t h e l e s s, we n e ed a d d i t i o n al " h a r d" data in t h is a r e a- d a ta on r a te of shoot and r o ot e l o n g a t i o n, clipping w e i g h ts and c o l or c h a n g e s. S e l e c t i ve C o n t r ol of G r a s s es A l t h o u gh f ew p r o b l e ms c u r r e n t ly e x i st r e l a t i ve to b r o a d- l e af w e ed c o n t r ol in t u r f, the s a me cannot be s a id f or the c o n- t r ol of unwanted g r a s s e s. M e t h o ds to s e l e c t i v e ly r e m o ve p e r- e n n i al g r a s s e s, s u ch as q u a c k g r a s s, b e n t g r a s s, o r c h a r d g r a ss and t i m o t h y, without d a m a ge to the d e s i r a b le s p e c i es h a ve not b e en found. H o w e v e r, the s e a r ch c o n t i n u e s, o c c a s i o n a l ly with s o me s u c c e ss ( b r o m a c il l o o ks p r o m i s i ng on o r c h a r d g r a s s ). M o st annual g r a s s es r e s p o nd w e ll to e x i s t i ng c h e m i c a l s. C r a b g r a ss in h o me l a w ns is s t i ll m u ch d i s c u s s ed by l a wn and g a r d en e d i t o rs but is r e a d i ly c o n t r o l l ed by s e v e r al c h e m i c a l s, i n c l u d i ng b e n e f i n, D C P A, b e n s u l i d e, s i d u r o n, A z ak and B a n d a n e. T h e se h e r b i c i d es a re a p p l i ed as p r e - e m e r g e n ce c r a b g r a ss c o n- t r o ls and c a u se no d i s c o l o r a t i on to e s t a b l i s h ed t u r f g r a s s e s. T h is c o n d i t i on is m u ch m o re p r e f e r a b le than the t e m p o r a ry y e l l o w i ng that u s u a l ly o c c u r r ed f r om the u se of the o l d er p o s t- e m e r g e n ce c r a b g r a ss c h e m i c a l s. In O n t a r i o, f a ll a p p l i c a t i on w i th b e n s u l i de or D C PA h as b e en j u st as e f f e c t i ve as e a r ly s p r i ng t r e a t m e n t s. A z ak h as c a u s ed m a r k ed d a m a ge to the t u rf w h en a p p l i ed in the f a l l, and b e n e f in and s i d u r on a re e f f e c t i ve the f o l l o w i ng s p r i n g. i n- A n n u al b l u e g r a ss ( P oa annua L.) is c o n s i d e r ed a p r o b l em by m a ny golf s u p e r i n t e n d e n ts in the n o r t h e rn U. S. and C a n a d a. It is found in golf g r e e n s, w h e re it p r e s e n ts a d i f f e r e nt t e x t u re t h an b e n t g r a s s, and is p a r t i c u l a r ly u n d e s i r a b le b e c a u se s o m e t i m es k i l ls out r a p i d l y, l e a v i ng b a re a r e a s. On the o t h er hand, s o me s u p e r i n t e n d e n ts f e el t h ey k n ow how to " m a n a g e" a n n u al b l u e g r a ss and find it u s e f ul b e c a u se it g r o ws r a p i d ly the s p r i n g, f i l l i ng in a r e as that w e re k i l l ed by d e s i c c a t i on or s n ow m o l d. in it T he " c r a b g r a ss h e r b i c i d e s" m ay g i ve good c o n t r ol of P oa annua u n d er s o me c o n d i t i o n s. At o t h er t i m es t h ey do not. is s t i ll u s ed with good r e s u l ts by- T r e a t m e nt with a r s e n i c a ls m a ny golf c o u r s e s, but it is s l ow and i n j u ry m ay r e s u lt if e v en s l i g h t ly e x c e s s i ve a m o u n ts a re a p p l i e d. In addition, the t o x i- c i ty of the a r s e n i c a ls h as put t h em u n d er s o m e w h at of a cloud at the p r e s e nt t i m e. T h u s, it would a p p e ar that b e t t er m e t h o ds a re r e q u i r ed to s e l e c t i v e ly r e m o ve annual b l u e g r a ss b e n t g r a s s. f r om F o r m u l a t i o ns T he f i r st 2 , 4 -D f o r m u l a t i on c o m m e r c i a l ly a v a i l a b le w as the o i l - s o l u b le e s t e r. W i d e s p r e ad d a m a ge to s u s c e p t i b le c r o ps f r om t h is v o l a t i le liquid soon l ed to i ts u se being r e s t r i c t ed to a r e as r e m o te f r om s u ch c r o p s, and to the d e v e l o p m e nt of the l ow v o l a t i le s o d i um s a lt and a m i n es of 2 , 4 - D. T h is t r e nd t o w a rd f o r m u l a t i o ns that a re l e ss l i k e ly to v a p o r i ze h as continued t h r o u g h o ut the y e a rs as o t h er h e r b i c i d es u s e f ul on turf h a ve b e en d e v e l o p e d. T h e re a re v e ry f e w, if a n y, e s t er f o r m u l a t i o ns s t i ll s o ld t o d ay f or u se on t u r f. G r a n u l ar f o r m u l a t i o ns of t u rf h e r b i c i d es h a ve b e en p r o- is f e r t i l i z e r. Such h e r b i c i d e - f e r t i l i z er c o m b i n a t i o ns d u c ed on a w i de r a n ge of c a r r i e r s. C u r r e n t l y, the m o st p o p u l ar c a r r i er m a ke good s e n se as t h ey not only r e d u ce the e f f o rt of a p p l i c a t i o n, but the f e r t i l i z er h e l ps c o n t r ol the w e e ds by s t i m u l a t i ng the d e- s i r a b le g r a s s e s. B o th " l i g h t - w e i g h t" and " h e a v y" g r a n u l ar f o r m- u l a t i o ns a re on the m a r k et with l i t t le or no d i f f e r e n ce in e f f e c t i v e- n e ss n o t i c e a b le in r e s e a r ch t r i a l s. M i x t u r es of h e r b i c i d es with o t h er p e s t i c i d es h a ve b e en t e s t ed f or u se on t u r f, and a re c o m m e r c i a l ly a v a i l a b l e. T h e re would s e em to be m e r it in s o me of t h e se m i x t u r e s, but with o t h e rs the b e n e f i ts a re dubious. A d d i t i o n al r e s e a r ch is r e q u i r ed on p o s s i b le i n t e r a c t i o ns of the c o m p o n e n ts of t h e se m i x t u r e s, and w h e t h er t h ey c an be a p p l i ed at a t i me that is s a t i s f a c t o ry f or obtaining good r e s u l ts f r om a ll c o m p o n e n ts of the m i x t u r e. F or e x a m p l e, a m i x t u re of a p r e - e m e r g e n ce c r a b g r a ss h e r b i c i de and a p o s t- e m e r g e n ce b r o a d l e af h e r b i c i de cannot be a p p l i ed in o ur g e o g r a p h ic r e g i on at a t i me that w i ll g i ve c o n t r ol of both t y p es of p l a n t s. G r o w th R e g u l a t o rs S e v e r al c h e m i c a ls a re c u r r e n t ly b e i ng t e s t e d, and two a re b e i ng u s ed by golf c o u r se f or g r a ss g r o w th r e t a r d a t i o n. An i d e al c h e m i c al would inhibit the g r o w th of g r a ss at a d e s i r a b le h e i g h t, m a i n t a in a s u i t a b le g r e en c o l or and c o n t r ol w e e ds at the s a me t i m e. No s u ch c h e m i c al h as b e en found to d a t e, but the m o r p h a c t in m a t e r i a ls show s o me p r o m i s e, p a r t i c u l a r i ly f or u se on r o u g hs and h a r d - t o - m ow a r e as of the golf c o u r s e. tion, f a i r ly good d a n d e l i on c o n t r ol is g i v en by t h is c h e m i c a l. In a d d i- A p p l i c a t i on E q u i p m e nt f a r m s, M o st t u rf w e ed c o n t r ol c h e m i c a ls of the 2 , 4 -D type w e re o r i g i n a l ly a p p l i ed by an a i r - p r e s s u re s p r a y e r. T h is is s t i ll t r ue w h en t h e se h e r b i c i d es a re u s ed on golf c o u r s e s, t u rf p a r ks and r o a d s i d e s. H o w e v e r, the t r e nd h as b e en a w ay f r om s p r ay a p p l i c a t i o n s, as f ar as h o me l a w ns a re c o n c e r n e d. T he d i f f i c u l ty of m a i n t a i n i ng a s p r a y er f r om y e ar to y e a r, c o u p l ed w i th the f a ct that a s e p a r a te s p r a y er had to be kept f or h e r b i c i de u s e, m a de a h o m e o w n er v e ry r e c e p t i ve to o t h er t y p es of a p p l i- c a t i on e q u i p m e n t. T h u s, g r a n u l ar h e r b i c i d e - f e r t i l i z er c o m b i n a- t i o ns that c o u ld be a p p l i ed with a r e l a t i v e ly i n e x p e n s i v e, l o n g- l a s t i ng s p r e a d er h a ve b e c o me p o p u l a r. A l s o, p a r t i c u l a r i ly f or u r b an d w e l l e r s, a e r o s ol h e r b i c i de a p p l i c a t o rs h a ve found r e a dy a c c e p t a n c e. A s i m i l ar p i c t u re h as d e v e l o p ed w i th r e s p e ct to the a p p l i- c a t i on of p r e - e m e r g e n ce c h e m i c a ls f or c r a b g r a ss and P oa annua c o n t r o l. H e r e, e s s e n t i a l ly a ll h o m e o w n er u se is r e s t r i c t ed to g r a n u l ar m a t e r i a ls a p p l i ed with a f e r t i l i z er s p r e a d e r. Golf c o u r s es and p a r ks a p p ly a g r e a t er p r o p o r t i on of t h e se h e r b i c i d es as g r a n u l a rs than t h ey do the 2 , 4 - D - l i ke c h e m i c a l s, p r i m a r i ly b e c a u se of the f o r m u l a t i o ns a v a i l a b le and the f a ct that s m a l l er a r e as a re u s u a l ly i n v o l v e d. In the f u t u r e, the u se of a i r - p r e s s u re s p r a y e rs w i ll f u r t h er d i m i n i s h. G r a v i ty f l ow m a c h i n es or o t h er d e v i c es that w i ll r e- d u ce d r i ft h a z a r ds w i ll be u s ed by m o re golf c o u r s es and o t h e rs f or t r e a t m e nt of l a r ge t u rf a r e a s. A e r o s ol c o n t a i n e r s, f or a ll t h e ir e a se of u s e, w i ll not i n c r e a se in f a v or a m o ng h o m e o w n e rs b e c a u se of t h e ir l i m i t ed p o t e n t i al f or o t h er than " t o u c h - u p" c o n- t r o l. T h u s, the c u r r e nt t r e nd t o w a rd the a p p l i c a t i on of m o re h e r- b i c i d e - f e r t i l i z er m i x t u r es on l a w ns w i ll undoubtedly continue. L e g i s l a t i on We h a ve s e en the e f f e c ts of p r e s s u r es e x e r t ed by a s o m e- in the p a st f ew t i m es m i s i n f o r m ed public on s e v e r al p e s t i c i d es m o n t h s. T h e se p r e s s u r es w i ll continue and we c an e x p e ct that s o me of the h e r b i c i d es u s ed f or t u r f g r a ss w e ed c o n t r ol w i ll c o me u n d er f i r e. A l r e a dy we h a ve s e en 2,4, 5 -T banned f or s e v e r al u s es in both the U. S. and C a n a d a. E v en 2 , 4 -D has c o me under a cloud as a " p o t e n t i a l ly d a n g e r o u s" t e r a t o g e n ic agent. A ny c h e m- i c al that h as any a p p r e c i a b le p e r s i s t e n ce in the s o il is s u s p e c t, w h i ch would i n c l u de d i c a m b a. T h u s, our r e s e a r ch on t u r f g r a ss h e r b i c i d es m u st be o r i e n t ed m o re and m o re t o w a rd obtaining " h a r d" data on s u ch t h i n gs as l o n g - t e rm e f f e c ts and p o s s i b le t o x i c i ty to s o il o r g a n i s ms i es so p r e v a l e nt t o d a y. in o r d er to c o u n t e r a ct the s c a re s t o r- W E S T E RN C U R R E NT T R E N DS IN T U R F G R A SS W E ED C O N T R OL W a y ne W. Huffine D e p a r t m e nt of A g r o n o my O k l a h o ma State U n i v e r s i ty S t i l l w a t e r, O k l a h o ma 74074 T he c u r r e nt t r e n ds in t u r f g r a ss w e ed c o n t r ol in my s e c t i on of the c o u n t r y, and p e r h a ps a r e f l e c t i on of the w e s t e rn a r e a, h a ve not c h a n g ed m u ch in the l a st f ew y e a r s. We a re u s i ng p r a c- t i c a l ly the s a me p re and p o s t - e m e r g e n ce h e r b i c i d es that we did f o ur or f i ve y e a rs ago, and our m e t h o ds of a p p l i c a t i on a re about the s a m e. We h a ve c h a n g ed the t i me of a p p l i c a t i on in a f ew i n- s t a n c e s; e . g ., m i d - A u g u st i n s t e ad of a S e p t e m b er a p p l i c a t i on of m o st p r e - e m e r g e n ce h e r b i c i d es f or P oa annua c o n t r o l. We s t i ll u se D C P A, b e n s u l i d e, b e n e f in and d i p h e n a m id on our b e r m u d a- g r a ss t u rf f or annual g r a ss c o n t r o l, and 2 , 4 - D, s i l v e x, and d i- c a m ba f or the b r o a d l e a v ed p l a n t s. T he o r g a n ic a r s o n a t es a re u s ed f or the p o s t - e m e r g e n ce c o n t r ol of c r a b g r a ss spp.), sandbur ( C e n c h r us p a u c i f l o r u s ), j o h n s o n g r a ss ( S o r g h um h a l e p e n s e ), d a l l i s g r a ss ( P a s p a l um d i l a t a t u m) and n u t g r a ss ( C y- p e r us rotundus). T he c o n t a ct h e r b i c i d e, p a r a q u a t, is m o re w i d e- ly u s ed now f or the c o n t r ol of w i n t er annual p l a n t s, p a r t i c u l a r ly in d o r m a nt b e r m u d a g r a ss ( D i g i t a r ia t u r f. C o n s u m er U se of H e r b i c i d es T h e re is l i t t le doubt that the h o m e o w n e rs of t o d ay a re g e n- e r a l ly i n t e r e s t ed in the p r o d u c t i on of good t u rf and a re w i l l i ng to I think t h is is a r e- spend t i me and m o n ey to a c h i e ve t h is goal. f l e c t i on of the e c o n o my and the f r ee t i me p e o p le h a ve to spend w o r k i ng in t h e ir l a w n s. T o o, t h is is a v e ry i m p o r t a nt f o rm of r e l a x a t i on f or m a ny p e o p l e. D r. D a y t on L. K l i n g m a n, W e ed In- v e s t i g a t i o n s, U S D A, at a r e c e nt m e e t i ng in V i r g i n i a, c o m m e n t ed that t h e re is a l i m it to how m u ch m o n ey p e o p le w i ll spend on w e ed c o n t r o l. A l t h o u gh h o m e o w n e rs a re w i l l i ng to spend t i me and e n e r gy in the p r o d u c t i on of a r a t h er high q u a l i ty t u r f, I b e l i e ve t h ey w o u ld p r e f er to c o m b i ne as m a ny o p e r a t i o ns as p o s s i b l e, s u ch as the a p p l i c a t i on of h e r b i c i d es and f e r t i l i z e r, and m i n i- m i ze the n u m b er of o p e r a t i o ns r e q u i r ed p er y e a r. T h e re is s t i ll a n e ed f or h e r b i c i d es with l o w er c o n c e n t r a- t i o ns of a c t i ve i n g r e d i e n ts f or a g r e a t er m a r g in of s a f e ty in h o me l a wn u s e. E v en a m o ng t u rf r e s e a r ch w o r k e r s, t h e re is s o me r e l u c t a n ce to u se t r a n s l o c a t ed h e r b i c i d es f or b r o a d l e af w e ed c o n t r ol in m i d - s u m m er that a re h i g h ly c o n c e n t r a t e d, or p r e s e nt a d r i ft h a z a rd f or o t h er p l a n t s. T h is w o u ld be t r ue of d i c a m ba and 2 , 4 -D in s o me f o r m u l a t i o n s. H e r b i c i d es s u ch as t h e se e x h i b it m a x i m um a c t i v i ty w h en a b s o r b ed by plant l e a v e s, but t h ey a l so h a ve c o n s i d e r a b le a c t i v i ty in the s o i l. D i c a m ba u s ed a l o ne at r e c o m m e n d ed r a t es f or b r o a d l e af w e ed c o n t r ol c a u s i n g, in my opinion, s o me s e c o nd thoughts by the a v e r a ge h o m e o w n er on i ts u s e. is E c o l o g i c al C o n c e rn C o n c e rn by the g e n e r al p u b l ic o v er the e n v i r o n m e nt and p o l- d e c l i n i ng l u t i on p r o b l e ms s e e ms to h a ve r e d u c ed the u se of s o me a r s e n ic c o m p o u n ds on h o me l a w n s. H e r b i c i d es that a c c u m u l a te to t o x ic p r o p o r t i o ns in the s o il p r o f i le a r e, in g e n e r a l, p r o b a b ly in p o p u l a r i ty f or r e g u l ar u se in w e ed c o n t r ol p r o g r a m s. T he u se of f o am as a c a r r i er and a m a r k er f or h e r b i c i d es u s ed by the h o m e o w n e r, as w e ll as i n d u s t r i al c o n c e r n s, p e r h a ps w i ll p r o v i de a d e q u a te s a f e ty f or the m i d - s u m m er a p p l i c a t i on of t r a n s l o c a t ed h e r b i c i d es that a re now u s ed with s o me r e l u c t a n c e, or not at a l l. P e r h a ps we w i ll s ee a g r e a t er n u m b er c i d es w i th s y n e r g i s t ic a c t i v i ty b e i ng u s e d. A c o m b i n a t i on of s u ch h e r b i c i d es could, p e r h a p s, be u s ed at m u ch l o w er r a t es with e q u al or g r e a t er e f f e c t i v e n e ss than e i t h er of the m a t e r i a ls u s ed a l o n e. of c o m b i n a t i o ns of h e r b i- S u m m a ry T he c u r r e nt t r e n ds in t u r f g r a ss w e ed c o n t r ol in the w e s t e rn p a rt of the United S t a t e s, in my opinion, h a ve not c h a n g ed m u ch in the l a st f ew y e a r s. We a re u s i ng the s a me p r e- and p o s t - e m e r- g e n ce h e r b i c i d e s, plus m a y be one or t wo n ew o n e s, that we did f o ur or f i ve y e a rs ago. O ur m e t h o ds of a p p l i c a t i on a re about the s a m e, but we h a ve c h a n g ed the t i me of a p p l i c a t i on in a f ew i n- s t a n c e s. In g e n e r a l, the h e r b i c i d es D C P A, b e n s u l i d e, b e n e f in and d i p h e n a m id a re u s ed f or the p r e - e m e r g e n ce c o n t r ol of a n- nual g r a s s e s, with 2 , 4 - D, s i l v ex and d i c a m ba u s ed f or the p o s t- e m e r g e n ce c o n t r ol of b r o a d l e a v ed p l a n t s. T he contact h e r b i- c i d e, p a r a q u a t, is w i d e ly u s ed f or the c o n t r ol of w i n t er annual plants in d o r m a nt b e r m u d a g r a ss t u r f. A n e ed s t i ll e x i s ts f or h e r- b i c i d es with l o w er c o n c e n t r a t i o ns of a c t i ve i n g r e d i e n ts f or g r e a t er m a r g i ns of s a f e ty f or u se by h o m e o w n e r s. T h e re w i ll p r o b a b ly be m o re c o m b i n a t i o ns of h e r b i c i d es with s y n e r g i s t ic a c t i v i ty m a de a v a i l a b le f or g e n e r al u s e. T h e se w i ll p r o v i de e q u al or g r e a t er e f f e c t i v e n e ss than e i t h er m a t e r i al u s ed a l o n e, and at m u ch r a t e s. l o w er S O U T H E RN C U R R E NT T R E N DS IN T U R F G R A SS W E ED C O N T R OL E v e rt O. B u rt U n i v e r s i ty of F l o r i da P l a n t a t i on F i e ld L a b o r a t o ry F o rt L a u d e r d a l e, F l o r i da 33314 T he d e v e l o p m e nt of h e r b i c i d es f or u se in w a rm s e a s on t u r f g r a s s es h as b e en d i s t i n c t ly d i f f e r e nt f r om that in c o ol s e a- s on g r a s s es b e c a u se of d i f f e r e n c es in the s u s c e p t i b i l i ty to s o me of the m o re c o m m on t u rf h e r b i c i d e s. F or e x a m p l e, c e n t i p e d e- g r a s s, b a h i a g r a ss and St. A u g u s t i n e g r a ss a re not t o l e r a nt to the o r g a n ic a r s e n i c a l s. T he m o st c o m m on t u r f g r a ss along the Gulf C o a st r e g i o n, St. A u g u s t i n e g r a s s, is s u s c e p t i b le to the p h e n o xy h e r b i c i d es as w e l l. On the o t h er hand, the t r i a z i n es c an be s a f e- ly u s ed on St. A u g u s t i n e g r a s s, c e n t i p e d e g r a ss and z o y s i a g r a s s. E f f e c t i ve and s a fe h e r b i c i d es f or w e ed c o n t r ol in St. A u g u s- t i n e g r a ss w as not d e v e l o p ed until the e a r ly 1 9 6 0 ' s. T he f i r st e x p e r i m e nt to d e m o n s t r a te the t o l e r a n ce of St. A u g u s t i n e g r a ss to t r i a z i ne h e r b i c i d es w as c o n d u c t ed by R a l ph W. White, J r ., in 19 58. At that t i m e, m u ch of the St. A u g u s t i n e g r a ss sod w as h e a v- i ly i n f e s t ed with w a t er s e d ge ( K y l l i n g ia spp.). White t r i ed f i ve h e r b i c i d es and found s i m a z i ne g a ve outstanding c o n t r ol of w a t er s e d ge and o t h er w e e d s, with no i n j u ry to St. A u g u s t i n e g r a s s. L a t e r, t e s ts i n d i c a t ed that a t r a z i ne g a ve b e t t er p o s t - e m e r g e n ce c o n t r ol of d i c o t y l e d e n o us w e e ds than did s i m a z i n e. O. M. & Sons e m p l o y ed M r. White and, d u r i ng i960 and 19 61, e x t e n- s i ve t u rf w e ed c o n t r ol e x p e r i m e n ts w e re c o n d u c t ed throughout the South. ing a t r a z i n e) w as m a r k e t ed u n d er the n a me of Bonus f or St. A u g u s t i n e g r a s s. T he r a p id and w i d e s p r e ad a c c e p t a n ce of Bonus f or St. A u g u s t i n e g r a ss and a c o m p a n i on p r o d u c t, Bonus f or In 19 62, a c o m b i n a t i on f e r t i l i z e r - h e r b i c i de ( c o n t a i n- Scott D i c h o n d r a, added m u ch i m p e t us to the d e v e l o p m e nt of p r o d u c ts containing plant n u t r i e n ts and p e s t i c i d e s. T h u s, S c o t ts w as a p i o n e er in the d e v e l o p m e nt of a s a f e, e f f e c t i ve and e a sy to a p- p ly h e r b i c i de f or c o n t r ol of w e e ds in St. A u g u s t i n e g r a ss and d i c h o n d r a. In addition to the d i f f e r e n c es in t o l e r a n ce of w a r m s e a s on and c o o l s e a s on t u r f g r a s s e s, the p r o l o n g ed g r o w i ng s e a s on in the South p r e s e n ts o t h er p r o b l e m s. A n n u a ls do not a d h e re to the " p r e s c r i b- e d" l i fe c y c le f or a n n u a l s. F or e x a m p l e, in south F l o r i d a, c r a b- g r a ss g e r m i n a t es 12 m o n t hs of the y e a r. F or p r e - e m e r g e n ce h e r- b i c i d es to be e f f e c t i ve u n d er t h e se c o n d i t i o n s, it is u s u a l ly n e c e s- s a ry to m a ke t h r ee or f o ur a p p l i c a t i o ns a n n u a l l y. A l s o, c r a b g r a ss and o t h er annuals do not die a n a t u r al death a f t er p r o d u c i ng s e e d, but continue to be a p r o b l em f or t wo or m o re y e a r s. T he n u m e r o us s p e c i es of w e e ds p r e s e nt in s o u t h e rn t u r f g r a s- s es m a k es c o n t r ol d i f f i c u l t. M a ny of the w e e ds p r e s e nt in the N o r th a re a l so found in the South. In addition, s e v e r al s p e c i es i n d i g e n o us only in the South a re c o m m on p r o b l e m s. N e m a t o d e s, i n s e c ts and fungi f r e q u e n t ly w e a k en t u r f, a l l o w i ng w e e ds to b e c o me e s t a b l i s h e d. Sandy s o i l s, high t e m p e r a t u r e s, and winds c a u s i ng s e v e re m o i s t u re s t r e ss w e a k en t u r f g r a s s es and p e r m it i n v a s i on of drought t o l e r a nt w e e d s. T he condition outlined a b o ve e x p l a in why t u rf w e ed c o n t r ol is n e c e s s a r i ly "big b u s i n e s s" in south F l o r i d a. W h i le no one c h e m i c al is a p a n e c e a, e f f e c t i ve h e r b i c i d es a re now a v a i l a b le f or m o st s i t u a t i o n s. T he p r e - e m e r g e n ce h e r b i c i d e s, e x c e pt s i d u r o n, that a re u s ed on c o o l s e a s on t u r f g r a s s es c an a l so be u s ed on the w a r m s e a- son t u r f g r a s s e s. T he o r g a n ic a r s e n i c a ls and the p h e n o x ys c an be u s ed f or p o s t - e m e r g e n ce c o n t r ol of w e e ds in b e r m u d a g r a ss and z o y s i a g r a s s. P h e n o x ys a l so c an be u s ed on c e n t i p e d e g r a ss and b a h i a g r a s s. A t r a z i ne is the p r i m a ry h e r b i c i de f or u se in St. A u g u s t i n e- in g r a s s. T h is h e r b i c i de a l so c an be u s ed f or c o n t r ol of w e e ds z o y s i a g r a ss and c e n t i p e d e g r a s s. It p r o v i d es e f f e c t i ve p r e - e m e r- In addition, it w i ll g i ve g e n ce c o n t r ol of m o st annual w e e d s. p o s t - e m e r g e n ce c o n t r ol of the c o m m on b r o a d l e af w e e d s, e x- c e pt c r e e p i ng b e g g a r w e ed ( M e i b o m ia or D e s m o d i um spp.). R e c e nt t e s ts i n d i c a te that K e rb and H e r b an g i ve e f f e c t i ve and s a fe c o n t r ol of P oa annua in b e r m u d a g r a s s. T h e se °two h e r b i c i d es g a ve both p r e- and p o s t - e m e r g e n ce w e ed c o n t r o l. P r e s e n t l y, h o w e v e r, n e i t h er is l a b e l ed f or u se on b e r m u d a- g r a s s.