I M191 V €11.11” ‘qulIII I?! HIM" WWII. t” III HII‘IIIWI' I} 'I am“ ,1I'I-N I: -1 . HIV 1. EDI .‘l "u. I1‘LI211‘1 1 3 ‘ ‘M'J III ’ ’ L‘I‘ ’I'I‘u" ‘ f1)!“ 51:12::2 -- w, M m L2 5 :3: I ,1 .3, v“ A .-4' I ’17 .A , -. 1.... . -u u_. ~ . ff ‘I. It ‘ In. 175,11- “5:: 11111211111111 WI 1111: 1:4"I‘1I‘n (1"‘3 .1311, 11 1111 1 II C 3.2;“ I 99g’m‘II“ g’: 113% : fi .. ig’,’ :i‘§?- ~S'32L ' ~ . --. -. 11“,?“ ‘i-‘ ,3 .. o I .r L .21. ‘04 . -u . a. o nun-.3 ' ... . (my? . ‘ o . '''''' ,,,,, . v‘fr‘11.1511‘ 131;; "I I'l ';1I'III1<1|I :1" .IIIIIlp ”111111- ‘1'41911'11, Ixfixuzém hswarIim III M: IIIIII I I I 'I'fT I:I I' "Milly lmnmrlmnml 310737’0797 Fla-,9 This is to certify that the dissertation entitled GRASS CONTROL IN SOYBEANS [GLYCINE MAX (L.) Merr.] WITH SELECTIVE POSTEMERGENCE HERBICIDES presented by JAMES JUSTIN KELLS has been accepted towards fulfillment of the requirements for Crop & Soil Sciences Ph . D . d . egree in w ELI—Lev»... m1 9% ()0 Major professor DateJL-Lg-Lv :95 ’Clgv1 U Q ' MS U is an Afflnmm'w Action/Equal Opportunity Institution 0-12771 MSU LIBRARIES 13—— BEIURNING MATERIALS: Place in book drop to remove this checkout from your record. FINES will be charged if book is returned after the date stamped below. WSW ’ “V ' |~l?.~:’ 5/ GRASS CONTROL IN SOYBEANS [GLYCINE MAX (L.) Merr.] WITH SELECTIVE POSTEMERGENCE HERBICIDES BY James Justin Kells A DISSERTATION Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Crop and Soil Sciences 1982 ABSTRACT GRASS CONTROL IN SOYBEANS [GLYCINE MAX (L.) Merr.] WITH SELECTIVE POSTEMERGENCE HERBICIDES BY James Justin Kells Several selective postemergence herbicides provided excellent midseason quackgrass [Agropyron repens (L.) Beauv.] control and regrowth control 10 months after treatment. Early treatments in one year provided less midseason control and regrowth control than late treatments with most Of the herbi- cides tested. In another season, late treatments provided less control of quackgrass regrowth compared to early treat- ments. Sequential applications provided equivalent or greater quackgrass control than single applications Of the same total rate. Several antagonistic interactions resulted from herbicide applications in combination with acifluorfen {sodium 5-[2- chloro-4-(trifluoromethyl)-phenoxy]-2-nitrobenzoate} or bentazon [3-isoprOpy1-lH-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide]. Excellent postemergence annual grass control with flexibility in time Of application was Observed with each experimental herbicide evaluated. Soybean [Glycine max (L.) Merr.] injury was significantly greater for each treatment where acifluorfen was included in the spray mixture; however, this injury did not Significantly reduce yield. Herbicidal activity and James Justin Kells persistence from soil treatments with fluazifOp-butyl {(il-butyl 2-[4-[[5-(trifluoromethyl)-2-pyridinylJonyphenonyprOpanoate} was Observed. More rapid absorption Of l4C-fluazifOp-butyl was Observed l4C absorbed 6 h after in soybeans with 75% of the recovered treatment compared to 36% in quackgrass. Translocation Of the radiclabel 144 h after treatment was 16.5% and 14.1% in soy- beans and quackgrass, respectively. Data indicate that differential absorption or translocation did not contribute to the selectivity of fluazifOp-butyl. Quackgrass phytotoxicity from fluazifop-butyl was lower on plants at the five- to six- leaf stage compared to those at the two- to three-leaf stage. Significantly more 14C was removed in leaf washes from the Older plants 144 h after treatment. Herbicidal activity and foliar absorption of fluazifOp-butyl was significantly greater at 30 C compared to 20 C. Plants exposed to full light trans- located Significantly more 14C than plants maintained in the shade. Moisture stress significantly reduced quackgrass control with fluazifOp-butyl; however, no significant differences in absorption or translocation were Observed. ACKNOWLEDGEMENTS The author expresses Sincere appreciation to his major professor, Dr. William F. Meggitt, for his guidance, encouragement, and constructive criticism throughout this project; but particularly for the Opportunity Of associa- tion and involvement with weed control at Michigan State University. Gratitude is extendedtanr. Donald Penner for his enthusiasm and assistance in the laboratory aspects Of this project as well as assistance in the preparation Of this dissertation. The assistance Of Drs. B. D. Knezek, A. R. Putnam, and M. J. Zabik as guidance committee members is gratefully acknowledged. The technical assistance Of Mark Horny and Gary Powell is especially appreciated. Gratitude is extended to Diane Sorensen for typing this manuscript. A very Special thanks to my wife, Donna, for her technical assis- tance in the laboratory portion Of this project, for her love, understanding, and support and for her many sacrifices throughout this project. ii TABLE OF CONTENTS INTRODUCTI ON C 0 O O O O O O O O O O O O C O O O 0 CHAPTER I - REVIEW OF LITERATURE . . . . . . . . . . GENERAL INFORMATION ON HERBICIDES TIME OF APPLICATION . . . . . . . . . . . . . . HERBICIDE INTERACTIONS. . . . . . . . . . . . . Effect on herbicidal activity- - - - - . - Basis for antagonisms- - - - - . . . . . . ENVIRONMENTAL EFFECTS ON HERBICIDE ACTIVITY - - ADJUVANTS . . . . . . . . . . . . . . . . . . . ABSORPTION AND TRANSLOCATIONo - - . . - . - . - Environmental factors. . . . - . . . . . . PHYSIOLOGICAL EFFECTS . . . . . . . . . . . . . MECHANISMS OF SELECTIVITY . . . . . . . . . . . SOIL ASPECTS. . . . . . . . . . . . . . . . . . LITERATURE CITED. . . . . . . . . . . . . . . . CHAPTER 2 - SELECTIVE POSTEMERGENCE GRASS CONTROL IN SOYBEANS [Glycine max (L.) Merr.]- . - . . - . - . . ABSTRACT. . . . . . . . . . . . . . . . . . . . INTRODUCTION. . . . . . . . . . . . . . . . . . MATERIALS AND METHODS . . . . . . . . . . . . . General procedures for field studies - - - Quackgrass control field studies - . . - . Annual grass control field studies - - - - iii Page 13 16 16 19 20 22 23 25 26 27 28 32 42 42 45 46 47 48 49 General procedures for greenhouse studies. Soil activity and persistence studies. . . RESULTS AND DISCUSSION. . . . . . . . . . . . . Quackgrass control . . . . . . . . . . . . Annual grass control . . . . . . . . . . . Soil activity and persistence studies. . . LITERATURE CITED. . . . . . . . . . . . . . . . CHAPTER 3 - ABSORPTION, TRANSLOCATION, AND ACTIVITY OF FLUAZIFOP-BUTYL AS AFFECTED BY PLANT GROWTH STAGE, TEMPERATURE, LIGHT, AND SOIL MOISTURE. . . . . . . . ABSTRACT. . . . . . . . . . . . . . . . . . . . INTRODUCTION. . . . . . . . . . . . . . . . . . MATERIALS AND METHODS . . . . . . . . . . . . . Laboratory procedure with l4C-fluazifcp- butyl. . . . . . . . . . . . . . . . . . . Comparison of species. . . . . . . . . . . Comparison Of quackgrass growth stages . . Effect Of temperature. . . . . . . . . . . Effect of light. . . . . . . . . . . . . . Effect of soil moisture. . . . . . . . . . RESULTS AND DISCUSSION. . . . . . . . . . . . . Comparison of species. . . . . . . . . . . Comparison of quackgrass growth stages . . Effect of temperature. . . . . . . . . . . Effect Of light. . . . . . . . . . . . . . Effect Of moisture stress. . . . . . . . . LITERATURE CITED. . . . . . . . . . . . . . . . CHAPTER 4 - SUMMARY AND CONCLUSIONS. . . . . . . . . APPENDIX 0 o o o o o o o o o o o o o o o o o o o o 0 iv 50 52 54 54 62 72 79 81 81 83 84 85 87 87 87 88 88 89 89 94 102 107 112 116 117 122 Table LIST OF TABLES CHAPTER 1 General characteristics of selective postemergence grass herbicides for broad- leaved crops. . . . . . . . . . . . . . . CHAPTER 2 Selective postemergence herbicides applied at several rates and quackgrass heights including sequential applications and the resultant activity on quackgrass and soybean, 1980. . . . . . . . . . . . . . . . . . . Selective postemergence herbicides applied at several rates and quackgrass heights including sequential applications and the resultant activity on quackgrass and soy- bean, 1981. . . . . . . . . . . . . . . . Combinations Of selective postemergence broadleaf and grass herbicides and the resultant activity on quackgrass and soybean, 1980 . . . . . . . . . . . . . . Combinations of selective postemergence broadleaf and grass herbicides and the resultant activity on quackgrass and soy— bean, 1981. . . . . . . . . . . . . . . . Phytotoxicity on quackgrass in the greenhouse from fluazifOp-butyl in combination with X-77, oil concentrate, acifluorfen, or bentazon . Barnyardgrass and yellow foxtail control from selective postemergence herbicides as affected by rate and herbicide combinations with acifluorfen and bentazon, 1980 . . . Page 55 57 59 60 63 64 Table Page 7 Selective postemergence herbicides applied at several rates and plant heights and the resultant activity on barnyardgrass and giant foxtail, 1981. . . . . . . . . . . . . . 66 8 Phototoxicity on barnyardgrass in the greenhouse from fluazifOp-butyl applied at several rates and plant heights . . - - - . 67 9 Combinations of selective postemergence broadleaf and grass herbicides and the resultant activity on barnyardgrass, giant foxtail, and soybean, 1981 - . - - - - - - . . 69 10 Phytotoxicity on barnyardgrass in the green- house from fluazifOp-butyl in combination with X-77, oil concentrate, acifluorfen, or bentazon . . . . . . . . . . . . . . . . . . . 70 11 The effect of herbicide rate, plant popula- tion, and herbicidal activity in the soil on barnyardgrass control with fluazifcp- butyl in the greenhouse. . . . . . . . . . . . 75 12 Quackgrass control from soil applications Of fluazifOp-butyl to a sandy loam soil in the greenhouse. . . . . . . . . . . . . . . 77 CHAPTER 3 l The effect of time of treatment and sequential applications on quackgrass phytotoxicity with fluazifOp-butyl in the greenhouse 4 weeks after treatment. . . . . . . . . . . . . . . . 101 2 The effect Of plant growth stage, temperature, light, and moisture stress on absorption, translocation, and recovery of l4C-fluazifop- butyl in quackgrass 144 h after treatment- - - 103 3 The influence of temperature, light, and moisture stress on quackgrass phytotoxicity with fluazifOp-butyl 4 weeks after treatment . 106 vi LIST OF FIGURES Figure Page CHAPTER 1 1 Molecular structure of several selective postemergence grass herbicides in soybeans . . . . . . . . . . . . . . . . . . 7 CHAPTER 2 1 Herbicidal activity and persistence Of fluazifOp-butyl following application to a sandy loam soil. The indicator was barnyardgrass planted and harvested at 10 day intervals. Herbicidal activity is reported as a reduction in dry matter accumulation compared to the untreated control. . . . . . . . . . . . . . . . . . . 74 CHAPTER 3 1 Absorption of 14C following application Of l4C-fluazifOp-butyl tO quackgrass and SOYbeanS o o o o o o o o 0' o o o o o o o o o 9 l 2 Translocation of 14C following application of l4C-fluazifOp-butyl to quackgrass and soybeans . . . . . . . . . . . . . . . . . . 93 3 Translocation and distribution Of 14C- fluazifOp-butyl in quackgrass. Plant and corresponding radioautograph following harvest 6 h after treatment (A) and 144 h after treat- ment (B). Plant left, radioautograph right. The treated portion of the treated leaf is marked with an arrow . . . . . . . . . . . . 96 4 Translocation and distribution Of 14C- fluazifop-butyl in soybeans. Plant and corresponding radioautograph following harvest 6 h after treatment (A) and 144 h after treat- ment (B). Plant left, radioautograph right. The treated portion of the treated leaf is marked with an arrow - - - . - - - - - - . - 93 vii Figure Page Recovery of 14C following application Of l4C-fluazifOp-butyl to quackgrass and soybeans . . . . . . . . . . . . . . . . . . 100 The influence Of quackgrass growth sta e on translocation and distribution of 1 C- fluazifOp-butyl in quackgrass. Plant and corresponding radioautograph of quackgrass plants in the two- to three-leaf stage (A) and the five- to six-leaf stage (B). Plant left, radioautograph right. The treated portion Of the treated leaf is marked with an arrow . . . . . . . . . . . . . . . . . . 105 The influence Of tem erature on translocation and distribution of 4C-fluazifOp-butyl. Plant and corresponding radioautograph of quackgrass maintained at 20 C (A) and 30C (B). Plant left, radioautograph right. The treated portion of the treated leaf is marked with an arrow. . . . . . . . . . . . . . . . 109 The influence Of irradiance on translocation and distribution of l4C-fluazifop-butyl in quackgrass. Plant and corresponding radio- autograph Of quackgrass maintained under light irradiance Of 2801iE-m‘2-s"l (A) and 53uE-m-2-s-l (B). Plant left, radioautograph right. The treated portion Of the treated leaf is marked with an arrow . . . . . . . . 111 The influence of soil moisture on translocation and distribution of l4C-fluazifOp-butyl. Plant and corresponding radioautograph of quackgrass maintained at 6 to 10% (w/w) soil-moisture (A) and 21% (w/w) soil moisture (B). Plant left, radioautograph right. The treated portion of the treated leaf is marked with an arrow. 114 viii INTRODUCTI ON Soybeans [Glycine max (L.) Merr.]have become one Of the major agronomic crops in the United States and else- where. Similar tO other crops, adequate weed control is a prerequisite to production of maximum soybean yields. With the cost of production currently experienced by the producer, an effective and consistent program for weed control is essential to profitable production. Several herbicides are available as soil treatments to control broadleaved weeds and annual grasses in soybeans. Acifluorfen {sodium 5-[2-chloro-4-(trifluoromethyl)-phenoxy]- 2-nitrobenzoate} and bentazon [3-isopropyl-lH-2,1,3-benzo- thiadiazin-4(3H)-one 2,2-dioxide] are available for selective postemergence control of broadleaved weeds and diclOfOp-methyl {methyl 2-[4-(2',4'-dichlorophenoxy)phenoxy]propancate} can provide selective postemergence grass control; however, this herbicide has very little activity on perennial grasses such as quackgrass [Agropyron repens (L.) Beauv.]. Several experimental herbicides have been shown to provide effective postemergence control Of both annual and perennial grasses with little soybean injury. Postemergence applications of a grass control herbicide in combination with acifluorfen or bentazon is desirable since it would increase the weed spectrum controlled. Fluazifop-butyl {(:)-butyl 2-[4-[[5-(trif1uoromethyl)- 2-pyridinyl]oxy]phenoxy]propanoate} is one Of a number of selective postemergence herbicides which have herbicidal activity on annual and perennial grasses in broadleaved crops. Little is known about absorption and translocation Of this herbicide. The Objectives of this study were to: (a) evaluate the influence of factors including rate, time of application, sequential applications, and herbicide combinations on the efficacy and soybean tolerance of several selective post— emergence herbicides for quackgrass and annual grass control, (b) examine the soil herbicidal activity and persistence of fluazifOp-butyl, (c) compare the absorption and trans- location Of 14C-fluazifOp-butyl in quackgrass and soybeans, (d) examine the influence of factors including plant growth stage, temperature, light, and moisture stress on absorption, translocation, and activity Of fluazifOp-butyl on quackgrass. CHAPTER I REVIEW OF LITERATURE The past decade has seen the introduction and development of a new and important component to agronomic and horticultural production and research. Selective postemergence grass control in broadleaved crops represents a unique addition to the available methods for economic con- trol of weeds. Several graminicides are presently being developed in the United States and other countries throughout the World. A broad understanding of these compounds is important for their effective use in the agricultural community. GENERAL INFORMATION ON HERBICIDES General information on the history, herbicidal activity, and physical properties of diclofop-methyl {methyl 2- [4-(2',4‘-dichlorophenoxy)phenoxy]propanoate} (1,9), metriflufen {methyl 2-[4-(4'-trifluoromethyl phenoxy) phenoxyIpropanoate} (9), mefluidide {N-[2,4-dimethyl-5- [[(trifluoromethyl)sulfonyl]amino]phenyl]acetamide} (57), sethoxydim {2-[l-(ethyloxyimino)butyl]-5-[2-(ethylthio) propyl]-3—hydroxy-2-cyclohenen-l-one} (4), difenopenten {ethyl 4-[4-[4-(trifluoromethyl)phenoxy]phenoxy]-2-pentenoate} 3 17,42), RO-13 8895 {acetone 0-[D-[2-[p-(a.a,a-trifluoro-p- tolyl)oxy] phenoxy]propionyl]oxime} (44), CGA-82725 {2- propynyl 2-[4-[(3,5-dichloro-2-pyrindinyl)oxy]phenoxy] propanoate} (l9), NCI-96683 (Nissan Chemical Ind., LTD.) (63), NCI-96721 (Nissan Chemical Ind., LTD.) (63), Fluazifop— butyl {(i)-butyl 2-[4-[[5-(trifluoromethyl)-2-pyridinyl oxy]phenoxy]propanoate} (47,68), and Dow 453 {methyl 2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy propanoate} (28) are presented in Table 1. Chemical names and structures of herbicides whose chemistry has been released are given in Figure 1. Each of the herbicides previously discussed has been reported to have significant activity on certain grassy weeds and to exhibit some level of tolerance to broadleaved crops such as soybeans [Glycine max (L). Merr.]. It is important that certain comparisons be discussed between the compounds. For control of rhizome johnsongrass [Sorghum halepense (LL) Pers.], melfuidide has been found to be less effective than difenopenten (80,93,95,106), sethoxydim (45,77,80,93, 95,106) CGA-82725 (45), or RO-13 8895 (94). Sethoxydim has been reported to be more effective than difenopenten (40). 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Molecular structure of several selective postemergence grass herbicides in soybeans. Diclofop-methyl (HOE-23408) CH3 I Cl 0 O-CH-COOCH3 Cl methyl 2-[4-(2',4'-dichlorophenoxy)phenoxy]propanoate Metriflufen (HOE-29152) CH3 l CF3 O O-CH-COOCH3 methyl 2-[4-(4'-trif1uoromethyl phenoxy)phenoxy] propanoate Mefluidide (MBR-12325) CH3 NHSOZCF3 CH3 NHCOCH3 N-[2,4-dimethyl-5-[[(trifluoromethyl)sulfony1]amino] phenyl]acetamide Figure 1. Continued Sethoxydim (BAS-9052) O CH2 CH2 CH3 H3C CH3 I , , C=N-O-CH2-CH3 H3C CH \ /\ S CH2 OH 2-[1-(ethoxyimino)buty1J-5-[2-(ethylthio)propy1]-3- hydroxy-Z-cyclohexen-l-one Difen0penten (KR-80) CH3 l F3C O O-CHCH=CHCOOC2H5 ethyl 4-[4-[4-(trifluoromethyl)phenoxy]phenony-Z- pentenoate RO-l3 8895 CH3 CH3 l l F3C O O-CH-C-O-N=C l H O CH3 acetone 0-[D-[2-[p-(a,a,a-trifluoro-p-tolyl)oxy] phenoxy]propionyl]oxime Figure 1. Continued 10 11 CGA-82725 Cl CH3 cl 0 ' 40 / O-CH-C \‘ N I O-CHZ-CECH 2-propynyl 2-[4-[(3,5-dichloro-2-pyridinyl)oxy] phenoxy]propanoate Fluazifop-butyl (PP009) (:)-but 1 2-[4~[[S-trifluoromethyl)-2-pyridinyl]oxy] phenoxy propanoate Dowco 453 C1 F C O OCHCOOCH N ‘lllll CH3 methyl 2-[4-ll3-chloro-5-(trifluoromethyl)-2-pyridiny1] oxy]phenoxy]prOpanoate 12 For control of quackgrass [Agropyron repens (L.) Beauv.], Wyse (86) reported only limited control with mefluidide compared to metriflufen. Waldecker and Wyse (99) reported midseason quackgrass control to be signifi- cantly greater from RO-13 8895 than from difenopenten or sethoxydim. Westra and Wyse (102) reported greater control from sethoxydim than from difenopenten. Similar results were found for bermudagrass [Cynodon dactylon (L.) Pers.] control (104). In another study comparing sethoxydim, NCI-96683, fluazifop-butyl, RO-13 8895, and Dowco 453, Dekker (22) found fluazifop-butyl, NCI-96683, and Dowco 453 to be the most effective for control of quackgrass. For control of annual grasses, Gealy and Slife (33), using yellow foxtail [Setaria lutescens (Weigel) Hubb] as the test species, found difenopenten to be more effective than diclofop-methyl. In a later study, Oliver et a1. (65) compared several experimental herbicides for control of a number of annual grass species including barnyardgrass [Echinochloa crus-galli (L.) Beauv.]. They found that regardless of grass species or rate, the order of phyto- toxicity was Dowco 453, RO-13 8895, sethoxydim, fluazifop- butyl, and difenopenten. Although the results presented here are only a representative fraction of the data reported and differences exist in the comparisons, it does serve as an overview of these herbicides. 13 TIME OF APPLICATION It is generally accepted that control of annual grasses with diclofop-methyl decreases when the herbicide is applied at later growth stages (32,91,101,109). Rogers et a1. (73) found that many grass species were not susceptible to metriflufen at the three-leaf stage with susceptibility decreasing as plants developed. Many annual grass species have been found to become more tolerant to difenopenten as they advanced into tillering (42). Similar results were reported for sethoxydim (40). Hill and Peek (41) reported that plant growth stage is not an important factor in obtaining annual grass control with CGA-82725. In a study on large crabgrass [Digitaria sanguinalis (L.) Scop.] control, Himmelstein and Peters (43) found that RO-13 8895 and CGA-82725 were effective at all stages of application. Drew (30) reported that higher rates of fluazifop-butyl were required to control advanced growth stages of a number of annual grasses. In a study reported by Oliver et a1. (65), several annual grass Species including barnyardgrass, broad signalgrass [Brachiaria platyphylla (Griseb) Nash], giant foxtail [Setaria faberi (Herrm.)], goosegrass [Eleusine indica (L.) Gaertn.], grain sorghum [Sorghum bicolor (L.)], fall panicum [Panicum dichotomiflorum (Michx)], large crab— grass, and red rice [Oryza sativa (L.)] were treated with difenopenten, sethoxydim, RO-13 8895, fluazifop-butyl and Dowco 453. At the two- to four-leaf stage all of the herbicides 14 tested controlled all the grass species in the study. However, at the 5- to lS—leaf stage, none of the herbicides were effective on red rice, grain sorghum, giant foxtail or barnyardgrass. Plant growth stage has been shown to be an important factor in the control of perennial grasses such as johnson- grass with selective postemergence herbicides. Swisher and Kapusta (86) have reported greater johnsongrass control with metriflufen at the boot stage than with earlier applications. Similar results were reported by Down and Rieck (29). Rogers (76) reported a decrease in johnsongrass control with metriflufen when plants were past the boot stage at time of treatment. This suggests that a window of greatest control may exist where earlier or later treatments are less effective. Johnsongrass control with difenopenten has been reported to be reduced on 1- to 2-m tall plants compared to smaller plants (62). Early applications (15 to 20 cm) of sethoxydim, RO-l3 8895, and fluazifop—butyl were shown to be more effective than late (45 to 70 cm) applications (37). Rogers et a1. (76) suggested that johnsongrass control with later applications can be improved by increasing the rate of application. Studies have been conducted on the influence of plant growth stage on quackgrass control. Majek and Duke (49) reported no difference in quackgrass control with metriflufen between plants in the three—leaf and six-leaf stage. However, metriflufen has been reported to give slightly greater quackgrass control when applied to plants 10- to lS-cm tall 15 compared to 8- to 10-cm tall (24). Waldecker and Wyse (99) reported no difference in control between growth stages of quackgrass from 0.84 kg/ha rates of sethoxydim, difenopenten, or RO-l3 8895. Dekker and Anderson (22), however, found that sethoxydim, NCI-96683, RO-13 8895, fluazifop-butyl, and Dowco 453 were more effective on quackgrass when applied at the four- to five-leaf stage compared to the three- to four- leaf stage. Plant growth stage has been reported to have little influence on grass control with Dowco 453 (84). It is apparent that other factors such as rate and environmental factors, etc. influence grass control at different plant growth stages and may account for some of the discrepancies reported in the literature. Various studies have investigated sequential applications for more effective control of perennial grasses such as johnsongrass and quackgrass. Johnsongrass control with sequential applications was often greater than with single applications at the same rate for metriflufen (86), sethoxy- dim (51,77,93,94,96,97), difenopenten (87,93,94,95), RO-l3 8895 (5,41,94), CGA-82725 (41), and fluazifop-butyl (21,68). Sequential applications have been found to provide greater quackgrass control with sethoxydim (51,77,79,96,97, 102), difenopenten (102), RO-l3 8895 (5), and fluazifop- butyl (21). However Bhowmik and Doll (7) reported that sequential applications gave no added quackgrass control with sethoxydim, difenopenten, or CGA-82725. This observa- tion may be related to environmental conditions or the procedure followed in the study. 16 Cultivation as a substitute for the second herbicide application has been examined in several studies. Young and Wyse (112) found that a cultivation following treatment with metriflufen increased quackgrass control. Scoresby et a1. (80) found that johnsongrass control was increased from a cultivation following a postemergence application of difenopenten but not sethoxydim. However, McAvoy (51) reported that a timely cultivation following sethoxydim may increase control of perennial grasses such as johnson- grass and quackgrass. Westra and Wyse (102) found that single applications of sethoxydim or difenopenten followed by a cultivation gave similar quackgrass control to sequential treatments and both were better than single treatments alone. Waldecker and Wyse (99) found that a cultivation after treatment aided in quackgrass control more with difenopenten and sethoxydim than with RO-13 8895. Signifi- cant increases in yield have also been reported from cultivations following treatments of sethoxydim, RO-13 8895, and GSA-82725 (7). HERBICIDE INTERACTIONS Effect on Herbicidal Activity. Considerable research has been conducted in the area of herbicide interaction between selective postemergence herbicides for broadleaved crops, much of it with diclofOp-methyl. Reduced control of various annual grass species with diclofop-methyl was 17 observed when the herbicide was combined in a tank mixture with bentazon [3-iSOpropy1-lH-2,l,3-benzothiadiazin-4(3H)- one 2,2-dioxide] (6,15,72,107), desmedipham (ethyl m-hydroxy- carbanilate carbanilate) (26,59,202), MCPA (2-methyl-4- chlorophenoxyacetic acid) (59,69), 2,4-D [(2,4-dichlorophenoxy) acetic acid] (24,83,89,92) 2,4-DB [4-(2,4-dichlorophenoxy) butansic acid] (78), dinoseb [2-(l-methylprOpyl)-4,6- dinitrophenol] (6) and nitrofen (2,4-dichlorophenyl p- nitrophenyl ether) (10). No reduction in giant foxtail control was observed by Ritter and Harris (72) with tank mixtures of diclofop-methyl and acifluorfen {sodium 5-[2- chloro-4-(trifluoromethyl)-phenoxy]-2—nitrobenzoate}. These results may be due to the reported phytotoxicity of acifluor- fen itself on annual grasses such as giant foxtail (88). More difficult to explain, however, is the synergistic interaction between diclofop-methyl and bentazon on yellow foxtail reported by Shurtleff and Buchanan (83). Herbicide interactions such as these reported on diclofop-methyl have also been studied with a number of more resent postemergence grass herbicides. Dortenzio and Norris (26) reported decreased barnyardgrass control with metri- flufen when the herbicide was combined in a tank mixture with desmedipham. Antagonistic trends have also been ob- served with combinations of metriflufen with bentazon or acifluorfen for control of johnsongrass (29). However, no antagonism was observed between metriflufen and bentazon or acifluorfen for control of fall panicum. Shurtleff and 18 Buchanan (83) reported increased control of yellow foxtail, large crabgrass, wild oats [Avena fatua (L.)], and johnson- grass from combinations of metriflufen and dinoseb. This is in conflict with findings of Nalawaja et a1. (61) who reported reduced grass control from combinations of metri- flufen and dinoseb. Hartzler and Foy (38) reported a reduction in large crabgrass control when either bentazon or acifluorfen were combined with sethoxydim. Ritter and Harris (72) also reported on antagonism between sethoxydim and bentazon and between difenopenten and acifluorfen. In a study examining compatability of several postemergence broadleaf herbicides including bentazon and acifluorfen with several postemergence grass herbicides, Nalawaja et al. (60) found that combinations with any of the broadleaf herbicides de- creased yellow foxtail control from difenopenten and CGA-82725. Yellow foxtail control from sethoxydim was reduced only when the herbicide was combined with bentazon or desmedipham. Smith (84) has reported that Dowco 453 is compatible with bentazon and acifluorfen. Although most interactions between postemergence herbicides have been antagonistic, one synergistic interaction has been well documented. Reports indicate that combinations of mefluidide and bentazon are more effective for control of red rice than either compound used alone (103). It is apparent from examining antagonistic herbicide interactions that the rate of the grass herbicide is an important function in the intensity of any interaction. 19 Hartzler and Foy (38) indicated that antagonism between sethoxydim and bentazon or acifluorfen was lessened by increasing the rate of sethoxydim from 0.28 kg/ha to 0.56 kg/ha. In addition, Nalawaja et al. (60) suggested that antagonisms involving sethoxydim may have existed which were not detected due to the rate of sethoxydim used and the sensitivity of the grass being treated. Basis for Antagonisms. Woletatios and Harvey (108) suggested that the antagonism between diclofop-methyl and bentazon may be explained by lower 14C-diclofop-methyl uptake in leaves pretreated with a diclofop-methyl-bentazon mixture. Qureski and VanderBorn (69) reported that uptake of diclofop is reduced in the presence of MCPA. They also reported that MCPA inhibits deesterification of diclofop- methyl to the free acid diclofop, and accelerates the conversion of diclofop to inactive conjugates. In examining the antagonism between diclofop-methyl and 2,4-D, Todd and Stobbe (92) found translocation of 14C to roots and shoot apices of wild oat to be reduced following application of 2,4-D. They suggested that deesterification of diclofop- methyl to the free acid diclofop was inhibited by 2,4-D. They suggested that diclofop-methyl moved acropetally in the apoplast and was responsible for leaf tissue damage while the free acid diclofOp moved basipetally in the symplast and was responsible for inhibition of meristematic activity. 20 ENVIRONMENTAL EFFECTS ON HERBICIDE ACTIVITY The major environmental factors which have been examined include temperature, relative humidity and soil moisture. Nalawaja et a1. (59) reported that diclofop-methyl was more effective at 10C than at 30C for wild cat control, but was more effective at 30C than 20C for yellow foxtail control. McWhorter (52) reported no control of johnsongrass with metriflufen regardless of rate when plants were exposed to post treatment temperature of 16C. Much greater control was observed when the post treatment temperature was 24C or 32C. Young and Wyse (112) found phytotoxicity to quackgrass from 0.56 kg/ha or lower rates of melfuidide to be greater to plants with a post treatment temperature of 30C compared with 17C or 27C. Wills (104) reported a two-fold increase in difenopenten activity at 35C compared to 18C. The effect of relative humidity in conjunction with temperature has been studied by McWhorter (52) . He reported significantly greater johnsongrass control with metriflufen when the post treatment conditions were 24C and 100% relative humidity compared to 40% relative humidity. Wills (104) found sethoxydim to be most toxic on bermudagrass when the post treatment environment was 18C and 100% relative humidity and reported that difenopenten activity was often greater at 100% relative humidity than at 40% relative humidity. 21 In examining the effect of moisture stress on grass control Nalawaja et a1. (59) reported that in general, grass plants under moisture stress after application were more tolerant to diclofop-methyl. West et al. (101) re- ported reduced control of moisture stressed barnyardgrass with diclofop-methyl, especially under cool, slow growing conditions. On several species of annual grasses including yellow foxtail and barnyardgrass, Dortenzio and Norris (27) found a significant reduction in control with diclofop- methyl or metriflufen under a low moisture environment (2 to 3% above permanent wilt point). Norris (64) also found that the reduction in diclofop-methyl activity from moisture stress on wild oat was much less under 85 to 89% relative humidity compared to 30 to 35% relative humidity. Dry condi- tions have been reported to lengthen the time for symptoms to appear on perennial grasses from sethoxydim; however, the end result is the same (51). Ready and Wilkerson (71) reported that both initial control and regrowth control of johnsongrass with fluazifop-butyl was greater with plants grown under adequate moisture. The reduced control of plants under moisture stress may be related to the more developed leaf cuticle that would be expected under those conditions. The effect of rhizome fragmentation on perennial grass control with fluazifop-butyl has been examined by Plowman et al. (68). They reported excellent control of quackgrass and johnsongrass with fluazifop-butyl in a cultivated area where fragmentation of rhizomes had occurred. Also, the authors 22 indicated that higher rates were required to control johnsongrass when rhizomes remained unfragmented. Colby et a1. (21) stated that for effective control of johnson- grass, bermudagrass and quackgrass with 0.28 kg/ha to 0.56 kg/ha of fluazifop-butyl, thorough fragmentation of the rhizomes by tillage was necessary, and higher rates were required for undisturbed perennials. However, Wagner and Letendre (98) reported that additional fragmentation of quackgrass rhizomes by discing or rototilling did not increase control with fluazifop-butyl in field tests plowed the preceding fall. This observation may be confounded with one or more other important factors previously discussed. ADJUVANTS Increased activity from adjuvants have been reported for diclofop-methyl (59,66), metriflufen (52,61), sethoxydim (51,67,95,96,102), difenopenten (60,102), RO-13 8895 (3), CGA-82725 (7,19), fluazifop-butyl (20) and Dowco 453 (84). Most studies indicate that crOp oils or crop oil concentrates give the best results. However, Michieka and Ilnicki (56) found that fall panicum control with metriflufen was greater with a non-ionic surfactant than with crop oils. It is apparent that many factors such as rate and environmental conditions influence the need for an adjuvant. Umeda and Kapusta (95) reported that crop oil concentrate enhanced johnsongrass control with sethoxydim only at rates less than 0.56 kg/ha or when applied to more mature (76 cm) 23 plants. McAvoy (51) suggested that the addition of crop oil concentrate to sethoxydim would compensate for approxi- mately 0.28 kg/ha of the herbicide. Similar results were reported by Veenstra et a1. (96). Addition of surfactants to metriflufen increased johnsongrass phytotoxicity only under low (40%) relative humidity (52). It appears that adjuvants increase herbicidal activity by increasing the penetration of the herbicides into the leaves. Oil con- centrates may also increase activity by solubilizing a portion of the leaf cuticle to aid in penetration. This may be particularly important under dry conditions or with more mature plants where a more impermeable cuticle is expected. ABSORPTION AND TRANSLOCATION Absorption and translocation of diclofop-methyl in several species including barnyardgrass and soybeans have been reported by Boldt and Putnam (11). No difference in absorption or translocation was observed between the two species. Translocation was limited to less than 2% with 98% of the applied l4C remaining in the treated leaf. Campbell and Penner (16) reported that sethoxydim was rapidly absorbed and translocated to all plant parts of both johnsongrass and soybeans. Unlike diclofop-methyl or sethoxydim, 14C- mefluidide absorption and translocation has been reported to be greater in giant foxtail than in soybeans initially after treatment; however, this trend reversed after the first 24 h (8). 24 The length of the absorption period is an important factor to be considered. Absorption of l4C-diclofop-methyl was reported to continue over a 192 h period in green foxtail [Setaria viridis (L.) Beauv.], wild cat, wheat [Triticum aestivum (L.)] and barley [Hordeum vulgare (L.)] (91); however, 14C uptake ended within 48 h after treatment in soybeans (108). Campbell and Penner (16) found that the 14 duration of absorption of C-sethoxydim in quackgrass was 12 h or less with 90% of the applied 14C absorbed. The site of greatest absorption has also been examined. Young and Wyse (111) reported that both penetration and toxicity of diclofop- methyl was greater as the chemical was applied closer to the base of wild cat. Similar results were reported by Walter et al. (100). Wills and McWhorter (105) reported three to four times more distribution of 14C when l4C-mefluidide was applied to the stems compared to the leaves. Limited translocation of diclofop-methyl in both the symplast and the apoplast have been reported (82). Mefluidide translocation has been reported to be primarily in the phloem with movement to areas of high metabolic activity in giant foxtail and soybeans (8). However, McWhorter and 14 Wills (55) reported movement of C from l4C-mefluidide to be primarily acropetal in johnsongrass, soybean, and common cocklebur [Xanthium pensylvanicum (Wallr.)]. Both acropetal and basipetal movement of metriflufen were reported in 14 14 johnsongrass (53). Rapid translocation of C from C- sethoxydim in the phloem with accumulation in the metabolic 25 sinks of quackgrass has been reported (16). Fluazifop-butyl has been reported to be both xylem and phloem mobile (68). Environmental factors. McWhorter and Wills (55) reported that increasing post treatment temperature from 22C to 32C resulted in a two- to three-fold increase in absorption and an eight-fold increase in translocation of 14C from l4C-mefluidide in soybeans. An increase in relative humidity from 40% to 100% resulted in less than a two-fold increase in absorption or translocation. In johnsongrass, when no surfactant was used, an increase in temperature from 22C to 32C resulted in less than a two-fold increase in absorption and affected translocation only at 40% RH. The addition of adjuvants increased absorption and translocation of 14 C-mefluidide in johhsongrass, especially at lower relative humidity (55). McWhorter (53) reported a two- to four-fold increase in translocation of l4C-metriflufen when the post treat- ment temperature was 35C compared to 18C; however, translocation always represented less than 1% of the applied 14C. Relative humidity had little effect on translocation of l4C-metriflufen. Absorption was not greatly influenced by either temperature or relative humidity. Translocation of 14C in soybeans also responded similarly to temperature and relative humidity. More 14C was recovered from soybeans than from johnsongrass (53). Dortenzio and Norris (27) reported that, although soil moisture stress did effect control of several grass species 26 with diclofOp-methyl, no significant differences in absorption or translocation could be detected. However, regrowth data indicate that more rapid translocation of fluazifop-butyl occurred on johnsongrass plants growing under adequate moisture compared to those growing under moisture stress (71). PHYSIOLOGICAL EFFECTS Little is known of the physiological effects of postemergence grass herbicides for broadleaved crops; however, some information has been reported on certain herbicides. Diclofop-methyl has been shown to interfere with both cell division and cell elongation (46). This herbicide has also been reported to disrupt membrane integ- rity and inhibit chlorophyll synthesis (3). In addition, it has been reported that diclofop-methyl acts as a strong auxin antagonist (81). Studies indicate that metriflufen inhibits protein synthesis in corn [(§EE.TEX§ (L.)] and soybean tissue (14) and inhibits electron flow in isolated chloroplasts of corn and peas (l3). Johnsey and Harger (48) reported that following treatment with sethoxydim, johnsongrass plants initially stopped growing with the first symptoms of injury occurring in the meristem of treated plants. Sethoxydim has been shown to reduce photosynthesis and transpiration in corn (34); 27 however, this may be a secondary effect. In corn, inhibition of adventitious root initiation and growth, reduced elonga- tion of root and Shoot, and at low concentrations, inhibited chlorophyll synthesis have been reported (2). Hatzios (39) suggested that sethoxydim may act by modifying the lipid structure of plant membranes. Fluazifop-butyl appears to adversely interfere with ATP production (68). The meristematic area within the susceptible plants are the first to show symptoms of injury. Plant growth typically ceases after treatment with fluazifop- butyl (68). Mefluidide has been shown to act as a plant growth regulator in susceptible plants (54,57). Wilkinson (70) suggested that mefluidide may inhibit production of a precurser to gibberellin and thus suppress gibberellin biosynthesis. MECHANISMS OF SELECTIVITY In examining the mechansim of selectivity of diclofop- methyl, Todd and Stobbe (90) reported that the active form of the herbicide is the free acid diclofop. Shimabukuro et al. (82) reported that both wheat, a tolerant grass, and wild cat, a susceptible grass, converted diclofOp-methyl to diclofop. In wheat, diclofop was irreversibly ring hydroxylated and finally conjugated. However, in wild cat, diclofop was conjugated to a neutral glycol ester which may hydrolyze to reform diclofop. Boldt and Putnam (12) compared 28 metabolism of diclofop-methyl in barnyardgrass, a susceptible grass, wild proso millet [Panicum milliaceum (L.)], a moderately susceptible grass, longspine sandbur [Cenchrus longispinus (Hack.) Fern.], a tolerant grass, soybean and cucumber [Cucumis sativus (L.)], both tolerant broadleaved plants. Both tolerant and susceptible plants converted the herbicide to the free acid diclofop. Tolerant broadleaved plants ring hydroxylated diclofop followed by glucosidic conjugation. In susceptible grasses, diclofop was conjugated on the propionate side chain which was readily reversible. Reports indicate that retention, absorption, translocation or volatility are not selectivity mechanism of diclofop—methy1.(ll). Swisher and Corbin (85) suggested that differences in tolerance to sethoxydim between soybeans and johnsongrass may be related to reduced ability of johnsongrass cells to degrade the herbicide. The selectivity of fluazifop-butyl between grass and broadleaved plants is thought to be due to a rapid degradation followed by conjugate formation in broadleaved plants (68). Bloomberg and Wax (8) suggested that selectivity of mefluidide may be partially explained by differential absorption and translocation in tolerant and susceptible plants. SOIL ASPECTS Significant soil activity has been reported with diclofop-methyl (18,59) metriflufen (73), CGA-82725 (41), RO-13 8895 (44), NCI-96683 (63), Dowco 453 (28) and fluazifop- butyl (47,68). In every case, soil activity is considerably ‘29 less than foliar activity. However, it appears that the soil component may be an important consideration in the use of certain postemergence grass herbicides. Several factors have been examined relating to soil considerations such as persistence and soil mobility. Norris (65) found with the use of vermiculite on the soil surface that soil activity from a postemergence application of diclofop did not contribute to wild oat control. However, Nalawaja et al. (59) reported a 6% reduction in wild cat control when vermiculite covered the soil at time of treat- ment. Diclofop-methyl has been shown to be absorped through both shoots and roots in barnyardgrass (101). Diclofop-methyl residual was reported three weeks after treatment (18), but not eight weeks after treatment (109). Data also indicate dissipation to be more rapid under warm soil conditions (50,109). Soil temperature appears to be more important than moisture. The mobility of diclofop- methyl has been reported to be comparable to trifluralin (109); however, Mulder and Nalawaja (58) reported more 14C-diclofop than 14C-trifluralin. leachability of Rogers et al.(73) reported that 0.28 kg/ha of soil applied metriflufen provided 89% or greater control of a number of annual grasses including barnyardgrass and giant foxtail. A rate of 0.84 kg/ha provided 95% or greater control of johnsongrass. Metriflufen has been shown to provide similar control as trifluralin at the same rates on annual grasses (76). Dekker et al. (23) reported reduction in 30 control from both root and shoot uptake in barnyardgrass and yellow foxtail. More rapid decrease in activity was observed under soil moisture of 15% compared to 5% or 25% (75). The rate of degradation increased as temperature increased from 15C to 25C. Rogers and Talbert (74) found that herbicidal activity from 1.1 kg/ha of metriflufen per- sisted for 40 and 63 days in 1977 and 1978 respectively and suggested that the loss of activity was due primarily to microbial degradation. Mobility of metriflufen in soil was also reported (74). Within a column of silt loam soil, metriflufen moved 7.5 cm and 18.5 cm from 7.5 cm and 10.0 cm of water respectively. Sethoxydim has been found to provide very little herbicidal activity at postemergence use rates when applied to the soil (4,43,67). The soil persistence of sethoxydim is very short (4). NCI-96683 has been reported to have considerable soil activity but is very immobile in the soil and incorporation is necessary for good soil activity (63). Dowco 453 has good soil activity with sufficient soil per- sistence but requires two to four times higher rates than postemergence applications (28). Soil activity from CGA-82725 has been reported to be of little significance (19). FluazifOp- butyl has considerable soil herbicidal activity on annual grasses and will persist for several weeks from recommended rates (47). Useful soil activity can be obtained from rates of 0.56 kg/ha or higher (20). Results indicate an important 31 soil component of activity with fluazifop-butyl (68). The soil component of herbicidal activity appears to be adequate with certain herbicides to justify further examination. 10. ll. 32 LITERATURE CITED American Hoechst Corp. 1976. HOE-23408, technical information bulletin. American Hoechst Corp., Agric. Chem. Dept. Somerville, N.J. pp. 7. Asare-Boaneah, N. K. and R. A. Fletcher. 1982. Phyto- toxicity of sethoxydim on corn seedlings. Abstr. Weed Sci. Soc. Am., p. 90. Bagley, R. W., G. L. Genson, A. R. DeMur and H. D. Woofter 1980. RO-13-8895, a selective postemergence herbicide for grass control. Proc. North Central Weed Control Conf. 35:45. BASF Wyandotte Corp. 1980. Poast, technical information bulletin. 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H., W. F. Meggitt and P. F. Boldt. 1981. Soil herbicidal activity from HOE-29152 and diclofop applied postemergence. Weed Sci. 29:314-316. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 34 Dekker. J. H., W. F. Meggitt, P. F. Boldt and T. Malefyt. 1978. Soil herbicidal activity from postemergence applications of HOE-29152 and diclofop. Proc. North Central Weed Control Conf. 33:115. Doll, J. D. and D. C. Drost. 1977. New herbicides for quackgrass control in soybeans. Proc. North Central Weed Control Conf. 32:52. Dortenzio, W. A. and R. F. Norris. 1979. Antagonistic effects of desmedipham on diclofop activity. Weed Sci. 27:539-544. Dortenzio, W. A. and R. F. Norris. 1980. The influence of soil moisture on the foliar activity of diclofop. Weed Sci. 28:534-539. Dow Chemical Co. 1982. Dowco 453 ME, technical information bulletin. Dow Chemical Co., Midland, MI pp. 4. Downs, J. P. and C. E. Rieck. 1978. The evaluation of HOE 29152 for selective johnsongrass control. Proc. South. Weed Sci. Soc. 31:53 Drew, B. M. 1982. Postemergence fluazifop-butyl for control of grasses in Oilseeds and grain legumes. Abstr. Weed Sci. Soc. Am., p. 113. Fletcher, R. A. and D. M. Drexler. 1980. Interactions of diclofop-methyl and 2,4-D in cultivated oats (Avena sativa). Weed Sci. 28:363-366. Friesen, H. A., P. A. O'Sullivan and W. H. VandenBorn. 1976. HOE-23408, a new selective herbicide for wild oats and green foxtail in wheat and barley. Can. J. Plant Sci. 56:567-578. Gealy, D. R. and F. W. Slife. 1978. KK80-a post- emergence grass herbicide for soybeans. Proc. North Central Weed Control Conf. 33:46-47. Gealy, D. R. and F. W. Slife. 1982. Effect of selective postemergence grass herbicides on intact leaf photo- synthesis and growth of corn and soybeans. Abstr. Weed Sci. Soc. Am., p. 88-89. Glenn, S. and C. E. Rieck. 1977. Selective post- emergence johnsongrass herbicides for soybean production. Proc. North Central Weed Control Conf. 32:30. Glenn, S. and C. E. Rieck. 1977. The activity of mefluidide on johnsongrass and shattercane. Proc. South. Weed Sci. Soc. 30:54. 37. 38. 39. 40. 41. 42. 43. 44. 45. 46. 47. 48. 35 Harger, T. R., R. W. Prince and P. R. Nester. 1982. Comparison of BAS-9052, PP009 and RO-13-8895 for postemergence control of grasses in soybeans. Abstr. Weed Sci. Soc. Am., p. 6-7. Hartzler, R. G. and C. L. Foy. 1982. Evaluation of BAS 9052 OH alone and in combination with acifluorfen or bentazon for control of large crabgrass (Digitaria sanguinalis L.). Abstr. Weed Sci. Soc. Am., p. 5-6. Hatzios, K. K. 1982. Studies on the mode of action of the herbicide BAS 9052 OH. Abstr. Weed Sci. Soc. Am., p. 117. Helms, R. L., W. J. Blackmon and B. D. Reynolds. 1980. Comparisons of BAS 9052, KK-80 and MBR-18337 for the control of johnsongrass and annual grasses in cotton. Proc. South. Weed Sci. Soc. 33:55. Hill, E. R. and J. W. Peek. 1982. CGA-82725--a new grass herbicide for broadleaved crops. Abstr. Weed Sci. Soc. Am., p. 16. Hill, L. V. 1980. KK-80 a topical postemergence herbicide for use in cotton & soybeans. Proc. South. Weed Sci. Soc. 33:338. Himmelstein, F. J. and R. A. Petters, 1982. Non- incorporated herbicides for large crabtrass [Digitaria sanguinalis (L.) Scop.]. Abstr. Weed Sci. Soc. Am., p. 21-22. HLR Sciences,Inc. 1980. RO-l3-8895, technical information bulletin. HLR Sciences Inc., Maag Agro-chemicals Research and Development. Vero Beach, Fla. pp. 4. Hook, B. J. and S. Glenn. 1981. Selected herbicides for johnsongrass control in cropping systems. Proc. Northeast Weed Sci. Soc. 35:64. Hoppe, H. H. 1980. Effect of diclofop-methyl on the growth and development of Zea mays L. seedlings. Weed Research. 20:371-376. ICI Americas Inc. 1981. Fusilade, technical information bulletin. ICI Americas Inc., Agricultural Chemicals Division. Goldsboro, NC. pp. 41. Johnsey, P. S. and T. R. Harger. 1982. Visible and microsc0pic effects of BAS 9052 on johnsongrass [Sor hum halepense (L.) Pers.] and itchgrass (Rottboellia exa tata L.FT). Abstr. Weed Sci. Soc. Am., p. 85-86. 49. 50. 51. 52. 53. 54. 55. 56. 57. 58. 36 Majek, B. A. and W. B. Duke. 1979. Influence of the time of application and plowing of quackgrass [Agropyron repens (L.) Beauvglcontrol with glyphosate and HOE 29152. Proc. Northeast Weed Control Conf. 33:43. Martens, R. 1978. Degradation of the herbicide l4C diclofop-methyl in soil under different conditions. Pestic. Sci. 9:127-134. McAvoy, W. J., J. T. Thompson, W. G. Steinert, J. W. Daniel, J. F. Vesecky, L. W. Hendrick, M. A. Veenstra, W. J. Sciarappa, M. Schroeder and A. Tasker. 1980. Selective postemergence perennial grass control with BAS 9052 OH [2-(N-ethoxybutyrimidoyl)-5-(2-ethylthiopropyl)- 3-hydroxy-2-cyclohexen-1-one] in broadleaf crops. Proc. North Central Weed Control Conf. 28:13. McWhorter, C. G. 1979. The effect of surfactant and environment on the toxicity of metriflufen to soybeans (Glycine max) and johnsongrass (Sorghum halepense). Weed Sci. 27:675-679. McWhorter, C. G. 1981. Effect of tem erature and relative humidity on translocation of 4C-metrif1ufen in johnsongrass (Sorghum halepense) and soybean (Glycine max). Weed Sci. 29:87-93. McWhorter, C. G. and W. L. Barrentine. 1979. Weed control in soybeans (Glycine max) with mefluidide applied postemergence. Weed SCI. 27:42-47. McWhorter, C. G. and G. D. Willis. 1978. Factors affecting the translocation of 14C mefluidide in soybeans (Glycine max), common cocklebur (Xanthium ens lvanicum), and jOhnsongrass (Sorghum halepense). Weed SCl. : 8 -388. Michieka, R. W. and R. D. Illnicki. 1979. Chemical control of fall panicum (Panicum dichotomiflorum Michx.) in soybeans [Glycine max (L.) Merr:]with acifluorfen, HOE-29152 [2,4-(4-trifluoremethyl-phenoxy) phenoxy propanoate]and bentazon in combinations with spray adjuvants. Abstr. Weed Sci. Soc. Am., p. 14. 3M Co. 1980. MBR-12325, technical information bulletin. 3M Co., Agricultural Products, St. Paul, MN pp. 4. Mulder, C. E. G. and J. D. Nalewaja. 1977. Influence of moisture on diclofop applied to the soil. Proc. North Central Weed Control Conf. 32:114. 59. 60. 61. 62. 63. 64. 65. 66. 67. 68. 69. 70. 37 Nalewaja, J. D. K., A. Adamczewski, L. Garcia-Torres, E. Pacholak and S. D. Miller. 1976. Factors affecting HOE-23408 phytotoxicity. Proc. North Central Weed Control Conf. 31:132-134. Nalewaja, J. D., S. D. Miller and A. G. Dexter. 1980. Postemergence herbicide combinations for grass and broadleaf weed control. Proc. North Central Weed Control Conf. 35:43-44. Nalewaja, J. D., E. Pacholak, L. Liu and S. D. Miller. 1976. BAS-9021 and HOE-29152 for grass weed control. Proc. North Central Weed Control Conf. 31:137-140. Nester, P. R. and T. R. Harger. 1980. Postemergence activity of KK-80 on johnsongrass [Sorghum halepense (L.)] and itchgrass [Rottboellia exaltata (L.)] in soybeans. Abstr. Weed Sci. Soc. Am., p. 29. Nissan Chemical Industries, Ltd. 1980. NCI-96683, NCI-96721, technical information bulletin. Nissan Chemical Industries, Ltd. Tokyo, Japan. pp. 2. Norris, R. F. 1977. Influence of soil moisture on activity of diclofop-methyl. Abstr. Weed Sci. Soc. Am., p. 102-103. Oliver, L. R., D. G. Mosier and O. W. Howe. 1982. A comparison of new postemergence herbicides for control of annual grasses. Abstr. Weed Sci. Soc. Am., p. 17. O'Sullivan, P. A., H. A. Friesan and W. H. VandenBorn. 1977. Influence of herbicides for broadleaved weeds and adjuvants with dichlofop-methyl on wild cat control. Can. J. Plant Sci. 57:117-125. Pearson, J. O. 1980. Postemergence graminicide for broadleaf crops. Abstr. Weed Sci. Soc. Am. p. 114. Plowman, R. E., W. C. Stonebridge and J. N. Hawtree. 1980. F1uazifop-butyl--a new selective herbicide for the control of annual and perennial grass weeds. Proc. British Weed Control Conf. 17:29-37. Qureshi, F. A. and W. H. VandenBorn. 1979. Interaction of diclofop-methyl and MCPA on wild oats (Avena fatua). Weed Sci. 27:202-205. Rao, S. R. and T. R. Harger. 1981. Mefluidide-bentazon interactions on soybeans (Glycine max) and red rice (Oryza sativa). Weed Sci. 29:208-212. 71. 72. 73. 74. 75. 76. 77. 78. 79. 80. 81. 82. 38 Ready III, E. L. and J. Wilkerson. 1982. Postemergence control of rhizome johnsongrass [Sorghum halepense (L.) Pers.] with PP009 as effected by drought stress. Abstr. Weed Sci. Soc. Am., p. 15. Ritter, R. L. and T. C. Harris. 1981. Interactions of postemergence soybean herbicides. Proc. Northeast. Weed Sci. Soc. 35:63. Rogers, N. K., L. R. Oliver and R. E. Talbert. 1980. Response of selected grass weeds to metriflufen. Weed Sci. 28:540-542. Rogers, N. K. and R. E. Talbert. 1981. Dissipation and leeching of metriflufen under field and controlled conditions. Weed Sci. 29:561-565. Rogers, N. K., R. E. Talbert and L. R. Oliver. 1980. Conditions influencing the degradation of HOE-29152 [methyl 2-[4-(4-trif1uoromethyl phenoxy)phenoxy] propanoate]. Abstr. Weed Sci. Soc. Am., p. 111. Rogers, N. K., R. E. Talbert and L. R. Oliver. 1981. Johnsongrass (Sorghum halepense) control in soybeans (Glycine max) with metriflufén. Weed Sci. 29:291-296. Rogers, S. A. and J. P. Worthington. 1979. Evaluation of BAS 9052 and 9021 for johnsongrass control in soybeans. Proc. North Central Weed Control Conf. 34:10. Schreiber, M. M. and P. L. Orwick. 1977. Antagonistic action of 2,4-DB of diclofop-methyl. Abstr. Weed Sci. Soc. Am., p. 3. Sciarappa, W. J., Jr. 1979. Postemergence grass control in soybeans with BAS 9052 OH. Proc. Northeast Weed Sci. Soc. 33:10. Scoresby, J. R., L. E. Bendixen and G. L. Jordan. 1979. Control of johnsongrass using post applied experimental herbicides. Proc. North Central Weed Control Conf. 34:10. Shimabukuro, M. A., R. H. Shimabukuro, W. S. Nord and R. A. Hoerauf. 1978. Physiological effects of methyl 2-4(2,4-dichlorophenoxy)phenoxy)propanoate on oat, wild oat and wheat. Pestic. Biochem. Physiol. 8:199-207. Shimabukuro, R. H., W. C. Walsh and R. A. Hoerauf. 1979. Metabolism and selectivity of diclofop-methyl in wild oat and wheat. J. Agric. Food Chem. 27:615-623. 83. 84. 85. 86. 87. 88. 89. 90. 91. 92. 93. 39 Shurtleff, J. L. and G. A. Buchanan. 1979. Diclofop and HOE-29152 interactions with five herbicides. Proc. South. Weed Sci. Soc. 23:65. Smith, L. L. Jr., H. Johnston, B. C. Gerwick and E. A. Egli. 1982. Dowco 453--a new postemergence herbicide for selective annual and perennial grass control in broadleaved crops. Abstr. Weed Sci. Soc. Am., p. 107. Swisher, B. and F. T. Corbin. 1982. The behavior of sethoxydim in soybeans and johnsongrass [Sorghum halepense (L.) Pers.]. Part II. Uptake and metabolISm in cell cultures. Abstr. Weed Sci. Soc. Am., p. 93-94. Swisher, B. A. and G. Kapusta. 1980. Selective postemergence johnsongrass (Sorghum halepense) control in soybeans (Glycine max). Weed Sci. 28:529-534. Terhune, M. E. and R. E. Frans. 1980. Preliminary comparisons of KK-80 and BAS-9052 for overtop control of johnsongrass in cotton and soybeans. Proc. South. Weed Sci. Soc. 33:45. Tillett, T. C. 1978. Postemergence control of Setaria faberi in soybeans with acifluorfen. Proc. North Central Weed Control Conf. 33:67. Todd, B. G. and E. H. Stobbe. 1976. Basis of the antagonistic effect of 2,4-D on diclofop-methyl toxicity in wild oats. Proc. North Central Weed Control Conf. 31:40. Todd, B. G. and E. H. Stobbe. 1976. Selectivity of diclofop-methyl among wheat, barley, wild oats and green foxtail. Proc. North Central Weed Control Conf. 31:140. Todd, B. G. and E. H. Stobbe. 1977. Selectivity of diclofop-methyl among wheat, barley, wild oat (Avena fatua) and green foxtail (Setaria viridis). Weed Sci. 25:382-385. Todd, 8. G. and E. H. Stobbe. 1980. The basis of the antagonistic effect of 2,4-D on diclofop-methyl toxicity to wild oat (Avena fatua). Weed Sci. 28:371-377. Umeda, K. and G. Kapusta. 1979. Mefluidide, BAS 9052 and KK-80 for selective postemergence johnsongrass control in soybeans. Proc. North Central Weed Control Conf. 34:10-11. 94. 95. 96. 97. 98. 99. 100. 101. 102. 103. 40 Umeda, K. and G. Kapusta. 1980. Selective rhizome johnsongrass control in soybeans with soil applied and postemergence herbicides. Proc. North Central Weed Control Conf. 35:21. Umeda, K. and G. Kapusta. 1981. Postemergence rhizome johnsongrass [Sorghum halepense (L.) Pers.] control in soybeans with BAS-9052 [2-(N-ethoxybutrimidoyl)- 5-(20 ethylthiopropyl)-3-hydroxy-2-cyclohexen-l-one], difenopenten and mefluidide. Abstr. Weed Sci. Soc. Am., p. 11. Veenstra, M. A., J. F. Vesecky and L. W. Hendrick. 1978. BAS 9052 OH a new postemergence grass herbicide for soybeans. Proc. North Central Weed Control Conf. 33:69. Vesecky, J. F., L. W. Hendrick, M. A. Veenstra and R. E. Ascheman. 1979. BAS 9052 OH for postemergence control of annual and perennial grasses in field crops. Proc. North Central Weed Control Conf. 34:34. Wagner, V. and G. J. Letendre. 1982. Postemergence quackgrass [Agropyron re ens (L.) Beauv.]control in broadleaf crops with TF 169 (butyl 2-[4-(5-trif1uoro- methyl-Z-pyridyloxy)phenoxy]propionate) in eastern Canada. Abstr. Weed Sci. Soc. Am., p. 18. Waldecker, M. A. and D. L. Wyse. 1980. Quackgrass control in soybeans. Proc. North Central Weed Control Conf. 35:10. Walter, H., W. Koch and F. Muller. 1980. Effect of type of application on the penetration and translocation of diclofop-methy in wild oats (Avena fatua L.). Weed Research 20:325-331. West, L. D., J. H. Dawson and A. P. Appleby. 1980. Factors influencing barnyardgrass (Echinocloa crus- galli) control with diclofop. Weed Sci. 28:366-371. Westra, P. and D. L. Wyse. 1979. Quackgrass control in soybeans with BAS 9052 and KK-80. Proc. North Central Weed Control Conf. 34:34. Wilkinson, R. E. 1982. Mefluidide inhibition of sorghum growth and gibberellin precursor biosynthesis. J. Plant Growth Regulation 1:85-94. 104. 105. 106. 107. 108. 109. 110. 111. 112. 41 Wills, G. D. 1981. Effect of environment on the toxicity of BAS-9052 [2-(N-ethoxybutrimidoyl)-5-(2- ethylthiopropyl)-3-hydroxy-2-cyclohexen-l-one] and KK-80 [ethyl-4-[4-[4-(triflouromethyl)phenoxy]phenoxy]- 2-pentenoate] to common bermudagrass (Cynodon dactylon L.). Abstr. Weed Sci. Soc. Am., p. 9. Wills, G. D. and C. G. McWhorter. 1976. Translocation of MBR-12325 in soybeans and cocklebur. Abstr. Weed Sci. Soc. Am., p. 14. Wilson, H. P. and T. E. Hines. 1980. Postemergence control of annual grasses in soybeans. Proc. Northeast Weed Sci. Soc. 34:6-10. Woldetatios, T. and R. G. Harvey. 1977. Diclofop and bentazon interactions on soybeans and annual weeds. Proc. North Central Weed Control Conf. 32:42-43. Woldetatios, T. and R. G. Harvey. 1980. Effects of bentazon, diclofop and bentazon plus diclofop on the uptake of l4C-bentazon and 14C-diclofop in corn, giant foxtail (Setaria faberi Herrm.) and soybeans. Abstr. Weed Sci. Soc. Am., p. 102. Wu, C. H. and P. W. Santelman. 1976. Phytotoxicity and soil activity of HOE-23408. Weed Sci. 24:601-604. Wyse, D. L. 1976. Quackgrass control in soybeans with postemergence herbicides. Proc. North Central Weed Control Conf. 31:92-93. Young, F. L. and D. L. Wyse. 1977. Evaluation of HOE- 21952 for quackgrass control in soybeans. Proc. North Central Weed Control Conf. 32:32-33. Young, F. L. and D. L. Wyse. 1980. Control of quack- grass (Agropyron repens) in soybeans (Glycine max) with HOE-29152. Weed SCI. 28:493-498. CHAPTER 2 SELECTIVE POSTEMERGENCE GRASS CONTROL IN SOYBEANS [Glycine max (L.) Merr.] ABSTRACT Several selective postemergence herbicides provided excellent midseason quackgrass [Agropyron repens (L.) Beauv.]control in 1980 and 1981. Control of quackgrass regrowth 10 months after application was observed in 1980 and 1981. Greatest regrowth control in 1980 was observed with sethoxydim {2-[l-(ethyloxyimino)butyl]-5-[2-(ethylthio) propyl]-3-hydroxy-2-cyclohenen-l-one}, RO-13 8895 {acetone O-[D-[Z-[p-(a,a,a-trifluoro-p-tolyl)oxy] phenoxy]prOpionyl] oxime}, and NCI-96683 (Nissan Chemical Ind., LTD.). Greatest quackgrass regrowth control in 1981 occurred with NCI-96683 and Dowco 453 {methyl 2-[4-[[3-chloro-5-(trifluoromethyl)- 2-pyridinyl]oxy]phenoxy]propanoate}. Early treatments applied to 7- to 9-cm tall quackgrass in 1980 were less effective than late treatments applied to 16- to 22-cm tall plants with each herbicide except NCI-96683 and NCI-96721 (Nissan Chemical Ind., LTD.). In 1981, early treatments applied to 9- to 13-cm tall plants provided similar midseason control as late treatments applied to 18- to 22-cm tall plants with each compound tested except RO-13 8895; however, 42 43 late treatments provided less control of quackgrass regrowth. In both years, sequential applications provided equivalent and in many cases greater midseason quackgrass control and regrowth control than single applications of the same rate for each of the herbicides evaluated. Several antag- onistic herbicide interactions resulted from grass herbicide applications in combination with acifluorfen {sodium 5- [2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoate} or bentazon [3-isopropyl-lH-2,1,3-benzothiadiazin-4(3H)- one 2,2, dioxide]. These antagonisms were partially overcome in 1981 by increasing the rate of the grass herbi- cide. Excellent postemergence control of annual grasses was observed with each of the herbicides examined in 1980 and 1981. Each of the herbicides evaluated in 1981 except diclofop-methyl {methyl 2-[4-(2',4'-dichlorophenoxy)phenoxy] propanoate}provided 90% or greater control of barnyardgrass [Echinochloa crusgalli (L.) Beauv.] and giant foxtail (Setaria faberi Herrm.) at rates of application of 0.14 kg/ha. Loss of control from herbicide combinations with acifluorfen or bentazon were less apparent on annual grasses. Field results indicate flexibility in time of application for annual grass control with each of the herbicides evalu- ated except diclofop-methyl. In each field study soybean [Glycine max (L.) Merr.] injury was significantly greater for each treatment where acifluorfen was included in the spray mixture. Soybean injury did not decrease soybean yield 44 compared to the hand weeded control. Soil applications of fluazifop-butyl ‘K:)-butyl 2-[4-[[5-(trif1uoromethyl)-2- pyridinyl]oxy]phenoxy]propanoate} at 0.28 kg/ha or higher provided 90% or greater control of barnyardgrass seed and quackgrass rhizomes. Herbicidal activity in the soil following application of fluazifop-butyl ranged from 10 days to 40 days with rates of application of 0.28 to 2.24 kg/ha, respectively. Results indicate that activity in the soil contributed to control of 4- to 6-cm tall barnyardgrass plants following postemergence applications of fluazifop-butyl. 45 INTRODUCTION Soybeans have become an important component of agricultural production in the United States and else- where. Maximum soybean production is often limited by interference from weeds including annual and perennial grasses. Quackgrass, an aggressive perennial grass, is a particularly serious problem in the northern United States and Southern Canada (10). Several annual grass species may also create barriers to maximum soybean yields. Several herbicides are available for soil treatments to control annual grasses in soybeans; however, diclofop-methyl is currently the only herbicide fully registered for selective postemergence grass control in soybeans. Diclofop- methyl has little activity on quackgrass (l). Foliar appli- cations of glyphosate [N-(phosphonomethyl)glycine] can provide excellent quackgrass control (2); however, this her- bicide is non-selective and cannot be applied as a broadcast treatment after the crop has emerged. Several experimental herbicides have been evaluated for selective postemergence grass control in soybeans. Many have been shown to be effective for control of both annual and perennial grasses with little crop injury (5,12). Grass control with diclofop-methyl was reduced when application was made to larger plants (16,18,21)- Sequential applications of sethoxydim (17,19) or difenopenten {ethyl 4-[4-[4-(trifluoromethyl)phenoxy]phenoxy]-2-pentenoate} (19) have been shown to be the most effective for quackgrass control. 46 Postemergence applications of a grass control herbicide in combination with a broadleaved weed control herbicide such as acifluorfen or bentazon is desirable since it would increase the weed spectrum controlled. However, reduced grass control has been reported when bentazon was added to Spray mixtures with diclofop-methyl (3,4,14,20), metriflufen {methyl 2-[4-(4'-trifluoromethyl phenoxy) phenoxy]propanoate} (6), or sethoxydim (7,14). Similar antagonisms were observed between acifluorfen and sethoxydim (7) or difenopenten (14). Previous studies have shown herbicidal activity in the soil with several herbicides including diclofop-methyl (11) and metriflufen (15). The objectives of this study were to: (a) evaluate the efficacy and soybean tolerance of several selective postemergence herbicides for quackgrass and annual grass control; (b) examine the influence of plant growth stage and sequential applications on control; (c) examine the effect of herbicide combinations with acifluorfen and bentazon on grass control and soybean tolerance; (d) examine the soil activity and persistence of fluazifop-butyl. MATERIALS AND METHODS Field studies on grass control in soybean with several selective postemergence herbicides were conducted during the summer of 1980 and 1981. Greenhouse studies on the herbicidal activity of fluazifOp-butyl were conducted in 1981 and 1982. 47 General procedures for field studies. Field trials were conducted in East Lansing, Michigan to evaluate the efficacy of several herbicides for selective postemergence control of annual grasses and quackgrass. All treatments were applied with a compressed air tractor sprayer using 730308l flat fan nozzles. The spray volume was 253 L/ha and the spray pressure was 324 kPa. All herbicide treatments except those involving acifluorfen or fluazifop-butyl were applied with an oil concentrate added to the spray mixture at 2.34 L/ha. FluazifOp-butyl treatments were applied with X-772 surfactant added to the spray mixture at 0.5% (v/v). With treatments involving herbicide combinations, the rate of application was 0.56 kg/ha for acifluorfen and 0.84 kg/ha for bentazon. Applications with bentazon always included oil concentrate at 2.34 L/ha. Plot size was four 75 cm wide rows by 9 m long. Quackgrass control and soybean injury were determined by visual observations. Certain studies were harvested and soybean yields were adjustedtx313.0% moisture. All trials were designed as a randomized complete block containing three or four replications. Visual evaluations and soybean yields were subjected to analsis of variance and treatment mean comparisons were made using Duncan's multiple range test. lSpraying Systems Co., Wheaton, IL. 2X-77 is a non ionic surfactant composed of a mixture of alkylaryl-polyoxyethylene glycols, free fatty acids, and isopropanol produced by Chevron Chem. Co., San Francisco, CA. 48 Quackgrass control field studies. In 1980, a quackgrass control study was conducted on a Colwood-Brookston loam in an area of high quackgrass density that had been undisturbed for 2 years. The study was moldboard plowed in April and was disked once and field cultivated twice on May 30, 1980. 'Harcor' and 'Weber' soybeans were planted immediately after final til- lage. Early postemergence (EP) treatments of sethoxydim, difenopenten, RO-13 8895, CGA 82725 {2-propynyl 2-[4-[(3.5- dichloro-Z-pyridinyl)oxy]phenoxy]propanoate}, NCI-96683, NCI- 96721 and herbicide combinations with acifluorfen or bentazon were applied on June 16, 1980 when quackgrass was 7 to 13 cm in height and soybeans were in unifoliolate growth stage. Late postemergence (LP) treatments of the same individual herbicides were applied on June 30, 1980. Quackgrass was 16 to 22 cm in height and soybeans were in one- to two-trifoliolate growth stage. Additional areas were treated on both June 16 and June 30, 1980. Soybean injury from early and late applica- tions were evaluated 10 days after treatment on June 27 and July 11, 1980, respectively. Midseason quackgrass control was evaluated 4 weeks after the late (LP) treatments on July 26, 1980. Soybeans were harvested and yields determined. Quackgrass regrowth control the following season was evaluated 10 months after treatment on April 30, 1981. The site of the 1981 quackgrass control study was on a Colwood-Brookston loam in an area with dense quackgrass. The area had been undisturbed for 7 years. The study area was moldboard plowed in the fall of 1980 and was disked 49 twice and field cultivated twice on May 21, 1981. 'Harcor' and 'Corsoy' soybeans were planted immediately after final tillage. Early and late postemergence application of sethoxydim, RO-l3 8895, fluazifop-butyl, NCI-96683, Dowco 453 and herbicide combinations with acifluorfen and bentazon were made on June 11 and June 25, 1981. Additional areas were treated on both June 11 and June 25. Corresponding quackgrass height at time of treatment was 9 to 13 cm and 18 to 22 cm for early (EP) and late (LP) treatments, respec- tively. Soybean growth stage for early postemergence (EP) treatments was one- to two-trifoliolate. On June 19, 1981 the study area was treated with a broadcast application of 2,4-D at 0.56 kg/ha to control broadleaved weeds. Soybean injury following the early treatments was evaluated 7 days after treatment on June 18, 1981. Midseason quackgrass control was evaluated 4 weeks after the late (LP) treatments on July 23, 1981. Quackgrass regrowth control the following season was evaluated 10 months after treatment on April 28, 1982. Annual grass control field studies. In 1980, an annual grass control study was conducted on a Marlette loam in an area of predominantly barnyardgrass and yellow foxtail [Setaria lutescens (Weigel) Hubb.]. 'Corsoy' and 'Weber' soybeans were planted on June 13, 1980. Postemergence treatments of sethoxydim, difenopenten, RO-l3 8895, CGA 82725, NCI-96683, NCI-96721, diclofop-methyl and herbicide combinations with acifluorfen or bentazon were applied on July 8, 1980 when the 50 grasses were 7 to 9 cm in height and soybeans were in two-trifoliate growth stage. Soybean injury and grass control were evaluated on July 18 and August 1, 1980, respectively. The 1981 annual grass control study was conducted on a Capac loam in an area of predominantly barnyardgrass and giant foxtail. 'Harcor' and 'Corsoy' soybeans were planted on May 29, 1981. Early postemergence (EP) treatments with sethoxydim, RO-13 8895, fluazifop-butyl, NCI-96683, CGA 82725, Dowco 453, diclofOp-methyl and herbicide combinations with acifluorfen or bentazon were applied on June 19, 1981 when grasses were 7 to 9 cm in height and soybeans were in two- to three-trifoliolate growth stage. Late postemergence (LP) treatments were applied on July 1, 1981 when grasses were 17 to 22 cm in height and soybeans were in five to six- trifoliolate growth stage. Soybean injury from early and late applications were evaluated 7 days after treatment on June 26 and July 7, 1981, respectively. Grass control was evaluated 3 weeks after the late (LP) treatments on July 21, 1981. Soybeans were harvested and yields were determined. General_procedures for greenhouse studies. Experiments were conducted to examine grass control with fluazifop- butyl. Grass species evaluated were barnyardgrass and quackgrass. Studies were conducted in the greenhouse under temperatures of approximately 25 C-day/20 C-night. Natural light was supplemented with metal halide lighting, with a l6-h photoperiod at an average photosynthetic photon 51 flux density of 280uE-m-2-s-l. Relative humidity ranged from 30 to 60%. A11 plants were surface irrigated with water to maintain the moisture level at or near field capacity. On a weekly basis, 50 ml of a soluble fertilizer solution (22.5%N - 22.5%P O5 - 22.5%K O, Zg/l) was added to 2 2 each pot. Herbicide application was made using a moving belt sprayer delivering 355 L/ha at a pressure of 206 kPa. Grass control was determined by visual observation 2 weeks after barnyardgrass treatments and 4 weeks after quackgrass treatments. All experiments were designed as a randomized complete block with four replications and were repeated. All values are the means of two experiments. Visual evalua- tions were subjected to analysis of variance and treatment means comparisons were made using Duncan's multiple range test. Quackgrass rhizome sections were planted and grown in lO-cm diamater plastic pots filled with greenhouse potting soil (1:1:1 soil, sand, peat). Applications were made to 9- to l3-cm tall quackgrass plants. Herbicide treatments consisted of fluazifop-butyl at rates of application ranging from 0.14 to 0.56 kg/ha in combinations with oil concentrate at 2.34 L/ha or X-77 surfactant at 0.5% (v/v). Treatments also included fluazifop-butyl in combinations with acifluorfen at 0.56 kg/ha or bentazon plus oil concentrate at 0.84 kg/ha and 2.34 L/ha, respectively. Quackgrass control was evaluated 4 weeks after treatment. Barnyardgrass was grown from seed in lO-cm diameter plastic pots containing a sandy loam soil with 75% sand, 52 12% silt, 13% clay, 0.8% organic matter, and a pH of 7.8. After emergence, 10 uniform and equally spaced plants were selected in each pot. Herbicide treatments were applied when plants were 4 to 6 cm, 8 to 10 cm, 13 to 15 cm or 17 to 19 cm tall. Herbicide treatments consisted of fluazifop- butyl at application rates of 0.07 to 0.56 kg/ha in combina- tion with oil concentrate at 2.34 L/ha. Herbicide treatments to 4- to 6-cm tall plants also included fluazifop-butyl in combination with X-77 surfactant at 0.5% (v/v), acifluorfen at 0.56 kg/ha, or bentazon plus oil concentrate at 0.84 kg/ha and 2.34 L/ha, respectively. Plants were evaluated for phytotoxicity 2 weeks after treatment. Soil activity and persistence studies. Barnyardgrass seeds were planted in lO-cm diamater plastic pots filled with a sandy loam soil with 75% sand, 12% silt, 13% clay, 0.8% organic matter, and a pH of 7.8. Seeds were planted at a rate of 20 seeds/pot. Immediately after planting, the pots were treated with soil applications of fluazifop-butyl at rates of 0.07 to 1.12 kg/ha in combination with X-77 surfactant at 0.5% (v/v) and were placed in the greenhouse under similar conditions as previously described. Barnyard- grass plants were harvested 10 days after planting and percent emergence and total shoot dry matter accumulation were determined. Reduction in emergence and dry matter accumula- tion compared to the untreated control were calculated. Immediately following harvest, the pots were replanted with barnyardgrass by inserting the seeds into the soil with a 53 2-mm diameter glass probe with as little disturbance of the soil surface as possible. This procedure was repeated every 10 days until six plantings and six harvestsluuibeen completed. In another study, barnyardgrass seeds were planted and grown in lO-cm diamater plastic pots filled with a sandy loam soil previously described. Plant densities were established at 3 plants/pot anui 50 plants/pot. To intercept the herbicide, vermiculite was added to the soil surface of one-half of the pots in the study prior to treatment and was removed imme- diately after treatment. Foliar spray treatments of fluazifop- butyl at rates of 0.07 and 0.14 kg/ha in combination with oil concentrate at 2.34 L/ha were applied to 4- to 6-cm tall barnyardgrass plants in pots with and without vermiculite on the soil surface. Barnyardgrass Control was evaluated 2 weeks after treatment. To evaluate herbicidal activity on quackgrass from soil applications of fluazifop-butyl, quackgrass rhizome sections were planted in 10-cm diamater plastic pots filled with a sandy loam soil previously described. Immediately after planting, soil applications of fluazifop-butyl were made at rates of 0.14 to 2.24 kg/ha in combination with X-77 surfac- tant at 0.5% (v/v). Quackgrass control was determined by visual evaluation and Shoot emergence was counted 15 and 45 days after treatment. 54 RESULTS AND DISCUSSION Quackgrass control. In 1980, late postemergence (LP) applications of sethoxydim, difenopenten, and RO-13 8895 at 1.12 kg/ha provided 76% or greater midseason control of 16- to 22-cm tall quackgrass (Table 1). Late postemergence (LP) and sequential (EP + LP) application of sethoxydim, difenopenten, RO-l3 8895 or CGA-82725 gave significantly greater midseason quackgrass control than the same rates applied early (EP) to plants 7 to 13 cm tall. Sethoxydim and RO-l3 8895 at rates of 1.12 kg/ha and NCI-96683 at 2.24 kg/ha provided 85% or greater control of quackgrass regrowth the following spring, regardless of time of application. Quackgrass regrowth control from difenopenten at 1.68 kg/ha was significantly lower from early (EP) treatments than from late (LP) or sequential (EP + LP) treatments at the same rate. CGA-82725 did not provide adequate midseason quack- grass control or quackgrass regrowth control in 1980 regardless of rate or time of application. All treatments significantly increased soybean injury compared to the uncultivated control. Greatest soybean injury was observed with late postemergence (LP) treatments of NCI-96683 and NCI-96721 with injury visually evaluated as high as 38%. However, this injury did not result in a significant yield reduction compared to the hand weeded control (Table 1). In 1981, late postemergence (LP) treatments of sethoxydim, RO-13 8895, fluazifop-butyl, NCI-96683 and Dwoco 453 at 1.12 55 .ucofiuoouu amcww Houun what om sawumnam>o Acsmfl>m .Aammu .on Haum¢. newammn one: manoeummuu Ann. cued on» nouuc m:»:0& ca :ofiuosam>o Acsmw>u .Aomma .on aasn. newammu who: mucosucouu Amqv mama any “mama mxoo3 v newumnam>0 acsmw>o .Aomma .om Danny uncommon oumHOAHONMuuno3u ou loco can wucumxoosu Hana EUINN ou nod Ou vagamom mum: mucosucouu and. oocomuoeoumoa mango .Aomma .oa econ. mcmon>0m oum~0wH0wacs can mucuoxocsv Hana Sound 0» up 0» emaadmu who: mucoaucouu .mm. oucouH060umom auucmo .c:\q vn.~ an cumuucoocoo HMO COCDHOCA nuccsunwuu ova0wnuo: Adda .umou «mama memwuaae m.:co:=n Ou madcuooom xuwaflnwn0um.wo HO>OH mm may um acououuflp muucmofiuwcmfim no: out nouuo~ COEEoo c >n 0030~H0u :0wua9~m>o cc cwcuw3 mucosa namm nonn nmnn mo «a «a 066mm 066mm 660mm wood wood wood Houunoo venom: came 6mg can cod no as no No no «o 2o as 2o Houucoo 00...- m>wu ASUCD onmmm onmdm unamm uuao~ can n-6mH clams o-n~m «66mm noes oases 6-8mm on.n H~noalHoz namm mlnmw nmumm «-uam we.” HueomuHoz onmmm onmmm numm ciaam noun «an «we was «as oanm enema uuaae v~.~ anaemiuoz comm enema com nummm ~H.H mmoeaunoz onaom onmw chasm u-am~ «Imam mso- ammN Agnew Armo~ «nude “wean Hxn~ NH.” m~e~mucoo cream numoa «smcw ANN om.o mmh~oucuo amen unmom onaan nuoma uuaow were sea was com u-unm cacao Hxflon -.H mama manom namm onmdm uuoma alum mom was mine» axon om.o mama nduom onaan onmw ono~m a-noa munm~ “noma amumm :munm an enema «undo Hxflen SG.H couemaoeouao onmnm canon “lead “lama amen fic~a «numm Hmw -.H couaodocmuao canon puma been “long enema filmed ova mm» «mm Human wince gage. -.H aacaxonumm «mm 6mm ona~n flnu~fl “ink“ «iced na~o muoNv canoe elude human «nave om.c aacsxonuom .ooa x mn\mx. 1w. .mnxmx. mq+mm 3 mm Ban 3 mm STE .3 mm “3+?“ 03 0mm muom onwoflnumz upamaa coonamm mwuamcw cmonaom Houucoo :u30umou OHORucoo mmmumxomsu u nmflumxnufla :Ommwmfldx 6.0mma .cconaom can mmoumxomzv :o huw>wuoc accuaammu on» can mcoHucoAammm acaucwsoom onwpaao:w nusmao: mmcumxooso can amumu Huum>om um cowaamo moowownuo: monomHOEOumom o>wuom~om .H canoe 56 kg/ha provided 75% or greater midseason control of 18- to 22-cm tall quackgrass (Table 2). Greatest soybean injury occurred with NCI-96683 at 1.12 kg/ha with injury visually evaluated at 40%. Unlike the 1980 study, time of treatment or sequential applications did not influence midseason quackgrass control with any of the herbicides examined in 1981, except RO-13 8895. Late postemergence applications of RO-l3 8895 at rates of 0.56 and 1.12 kg/ha provided significantly greater midseason quackgrass control than the same rates applied early (EP) to plants 9 to 13 cm in height. Quackgrass regrowth control with sethoxydim and fluazifop- butyl at 0.56 kg/ha and with NCI-96683 and Dowco 453 at 0.28 kg/ha was significantly lower when the herbicides were applied late (LP) compared to early (EP) or sequential (EP + LP) applications at the same rate. This suggests that basipetal translocation to the quackgrass rhizome was lower for the late (LP) treatments. Differences in the effect of time of application and sequential treatments on midseason quackgrass control and quackgrass regrowth control between 1980 and 1981 may be partially related to environmental differences. These results also indicate that a window of greatest quackgrass control exists in terms of plant growth stage such that treatments earlier or later are less effective. For example, early postemergence (EP) treatments in 1980 applied to 7- to l3-cm tall quackgrass may have been applied before the plants reached optimum maturity for basipetal translocation 57 .Aamma .oH mean. unofiummuu nouwm mxmp h :oflumsam>m Husmw>u .Amwma .ow dwumcv camammc mums mucoaucouu AAA. wand 0:» Houum nausea OH scapusac>o Hmsmfl> u .Aawma .MN handy pawammm «H03 mucoEumouu and. muma on» Hound mxoo3 v :oflucsam>o Hmnmfi>o .Aamma .mN ocsuv nmmuoxomso Hana Eelwwxxuimu o» cowammn who: mucoEumouu AAA. cocmmuosoumom mung c .Admma .HH canny acmonhom mumHOAHOHAHuuozu ou loco can mmoumxomsv Ham» sound ou la 0» oofiammc mum3 mucoEummuu Ana. monomumeoumom aaummo ..>\>c am.c um usauoauusn naux can: coeaddu no: HananumouenmSHm .mg\q cm.~ an mumuucmocoo Hwo coosaocw HauSAIQOMHNasau maw>ao>cw omosu umooxw manoeumouu opwoaauon HH< n .umou omcmu oamwuasa m.:uo:=a on mcflouoooc auaawncnoum uo Ho>oa am on» an accumuufip SHH:COAMH:mwm no: can umuuma cosaoo a An CO3OHHOH co«ams~m>o an cwnuw3 mucosa no Ra Re so as me me Houuaoo omuu>auasuca «coma piano ounce Anna cacao NH.H mmv 00300 mocha mvh «anon cacao mam Carma piano om.o mmv oozoo clown xuoom amp muons promo mu.o mmv 00300 rev oicmm cicmw anew mmm carom cummm ~H.H mooomiHoz oncwm onuvo xnpom onwhm nomm oncmm clamp om.c mmowannoz nonm~ ximna Olmmm curmw clash mN.o nmommiHUz onnwm ans «lawn «loam chm pnmmo onmcm NH.H AxuSQIQOHANcSHm «one ouumm xm mnemm 6mm mucus Gamma om.o AxuSQIQOMHnmSHm owe nuoem gm xuumw canes mua~h ounce m~.o Hananudouennaam comm ounce xenoa anamv picam 6mm cinho NH.H mmmoioHlom canwm oncoc xlnma xlwaw oicmm carom unomm mm.o mamminalom Henna xnm xiomw cacao Olmwh o~.o mama male“ we mica. xlgma xipcm ncmm crumb promo ~H.H Bfip>xosuom we xucom :mwm nlohm Clamp mucom clump om.o Sfipaxonuom no xflae Ewan wen uummm m~.o shesxonumm 1a. inexmx. mm m4+mm mg mm mq+mm can can Guam onwownuo: onusflca Houusoo auscumcu Houucoo mmmumxomsm cmonaom u mmmumxooso acmmmmcfi: m.amma .cmonaom can amoumxomso :o >ua>wuom uncuasmou mzu can unawucowammu Howuaonvom mcficsaocw mucmflon mmmumxomzv can moucu acum>mm an omaaomn nonwownuon oucomumfiwumom o>wuooHom .~ manna 58 of the herbicide. In addition, some quackgrass shoots may have emerged after treatment. This window of greatest control appears to be wider for certain herbicides with the greatest flexibility in time of application observed with NCI-96683 and NCI-96721 in 1980 and with NCI-96683 and Dowco 453 in 1981 (Tables 1, 2). In both 1980 and 1981, sequential applications were as effective or more effective than a single application of the same rate for each of the herbicides evaluated (Tables 1, 2). This agrees with results reported by Westra and Wyse (19). The addition of acifluorfen to a tank mixture with RO-l3 8895 at 0.56 kg/ha resulted in a significant reduction in midseason quackgrass control in 1980 (Table 3). In addition, quackgrass regrowth control was significantly reduced when either acifluorfen or bentazon was added to a spray mixture with sethoxydim at 0.84 kg/ha or RO-13 8895 at 0.56 kg/ha. Herbicide combinations with acifluorfen significantly increased soybean injury with all treatments with injury ranging from 50 to 58%. In addition, acifluorfen added to a spray mixture with difenopenten at 1.12 kg/ha significantly reduced soybean yield; however, this did not occur with sethoxydim or RO-13 8895 at the rates tested. In 1981, herbicide combinations with acifluorfen resulted in reduced midseason quackgrass control and quackgrass regrowth control with sethoxydim, RO-l3 8895 and fluazifOp- butyl at 0.56 kg/ha (Table 4). Acifluorfen in combination with NCI-96683 at 0.56 or 1.12 kg/ha did not reduce midseason 59 .Acmaa .hm 0:55. unoEumouu Houmw mast ca moms mm: :owumsam>m HMDMfi>n .Aamma .om Hflumdv unmeummuu Hmumm mnucos on moms mmz cofiumoam>m Hmsmw>m .Aomma .m~ haznv acmEucouu Hmumm mxooz 0 come mmz sewumsac>o Hmsmw> m .>Ho>fluoommou .mn\q vm.~ pom m£\mx vm.c um ousuxwe momma may on cocoa mno3 oucuucoocoo Hao can conucmmo mccon>om mucflaowwca can mucmam mmmumxomso Ham» EOIMH 0» In on oceammc muo3 mucmaummuu unfiownum: Hae .m£\mx om.o um ousuxwe hmumm 0:» on cocoa mc3 ammuosH0fio< v .mn\g vm.~ um musuxae human on» o» cocoa mm: ounuucmocoo Haoo .Aomma .oa 0G§bv n .ummu conch mamfluaae m.:monzn o» meflpuooom auwaflnonoum mo Ho>ma mm on» um acou000flp wauccowwficmflm Do: our HouuoH COEEoo m an to3oHHow :ofiumoam>o cc cwnufia m:mo£c amm mmm mmm oo oo oo nmm new ham Econ mood mood Houucoo 606003 0203 Ema an has no oo no no no no so we mo Houuaoo UOUM>HHHSOGD new new mam om Man an noom can use conmm mum minom om.o mama manom mam no~ mom paw Mam onma cowu cuma ou- Snood mumNH muomm ~H.H amucmdocmuao mum «on Man onma mom one oh~ Hana hues unnmu onmm am. «m.o aacxsoaumm load x ms\mx. lac .mn\mxc can our 60 can “cc co :mm Soc 60 com “cm 600 mama mcaoanumm moamfiw cmonxom nausflcw cmonaom Houucoo nu3ommmu Houucoo mmmumxomnm mmmumxomso acommomon ucmuasmou onu one nonwownum: m.omaH .comnaom can mmcumxomzo so >uw>fiuoo macho can womaocoun oozomuofioumom o>wuooHom mo meowumcwneoo .m wanna 60 .>Hm>fiuoommou .mn\q vm.~ can mn\mx cm.o um ousuxwe amumm on» on cocoa who: muouucoocoo HMO can acnmucom oucaoflaowwuuno3u ou loco can muccam mmmumxocso Hana Sound 0» Im on newsman mums mucosumouu ocwofinuon HH< .AHmmH .mH 0C5Uv UCQEHMQH“ Hmumfl mfiflc h 0005 m03 COfiHMDHM>U Hflfimfi> : .Ammma .mN kumo Hcsmw>m .Ammma .mm mazhv unusumouu umuuc mxooz o more no: newumsac>o Hmsmw> .mn\mx mm.o um musuxwfi human on» on cocoa mus commonawwo< .m:\A wm.~ um musuxfifi human 0:» o» cocoa mc3 cumuucmocoo Hwo u o c o .Aamma .HH mash. m:mona0m n .umou cocoa mamwuaos m.:mocso Cu onwpuoooc xuflaancnoum mo Ho>oH mm mnu um accumuwflo haucmowwflcmwm yo: who HmuuoH 205500 c an po3oHHOM :oHucoam>m an casua3 mccozm xo xo xo no no no no he no Homecoo omum>uuaaoca anmmm name “SSH clove ounce name Gimme canes name em.o mm. oozoa acumm mmm memos Linen siomm mop unamo camps 8mm NH.H mmommuHoz umom nape aroma close glued chasm muo~m mines onmme mm.o mmoomuHoz mmom name xflm nuomm no unavm «name “comm some om.o Hausnuaomaumsam momma venue Rm» slaw no gleam slows an enema m~.o asusnudouaumsdm onmme corms emmm rump aimed clams muons armmm Guano ~H.H mama manom mcmm onmme fluzmm aucNN no asefl~ munnm flared muomm em.o mama mauom roman amom xo anon anon gloom momma Anmmm ammo ~H.H sfiosxonumm Assam 66mm Re no so mnnem an “lama clamp Gm.o auosxonuom lmvllllllu lac .mnxmxv cam Goa oo cmm uo< oo mama choc ooo mums moHoAnumz c xuoncfi cmonaom odouucoo £u3oumou mucumxomso Houucoo mmcumxomsm m Gommmmoflz ucmuasmou ecu can nonwoflnuo: mmmum can woodcmoun mocmmuoEoumom o>fiuomacm uo mcoflumcwneou c.amma .cmwnhom can mmmumxooso :o >uw>fluom .4 manna 61 control but did reduce regrowth control. Herbicide combinations with bentazon resulted in reduced quackgrass control with sethoxydim at 0.56 and 1.12 kg/ha and with fluazifop-butyl at 0.28 kg/ha. In addition, reduced quack- grass regrowth control occurred with herbicide combinations of bentazon with sethoxydim at 0.56 kg/ha and with RO-13 8895 and NCI-96683 at 1.12 kg/ha. No loss of activity was observed from herbicide combinations with Dowco 453 at 0.56 kg/ha, the only rate tested. Similar to the 1980 results, soybean injury was significantly increased with each treat- ment where acifluorfen was added to the spray mixture. Midseason quackgrass control ratings in 1981 indicate that antagonistic herbicide interactions with acifluorfen or bentazon were partially overcome when the rate of the grass herbicide was increased (Table 4). For example, quackgrass control with sethoxydim in combination with bentazon was increased from 3% to 45% when the rate of sethoxydim was increased from 0.56 to 1.12 kg/ha. Similar increases in control were observed with fluazifop-butyl at rates of 0.28 and 0.56 kg/ha in combination with acifluorfen or bentazon. Similar results have been reported with sethoxydim (7). This response may explain why fewer antagonistic interactions were observed in 1980 where, in general, higher rates of the herbicides were used (Table 3). For this reason it is pos- sible that antagonistic interactions between Dowco 453 and acifluorfen or bentazon may occur at rates of Dowco 453 lower than 0.56 kg/ha. Quackgrass control with fluazifop-butyl 62 at rates of 0.14 to 0.56 kg/ha in the greenhouse was not reduced by addition of acifluorfen or bentazon to the spray mixture (Table 5). The lack of antagonisms with fluazifop- butyl may be related to different environmental conditions in the greenhouse. No significant differences in phytotoxicity on quackgrass with fluazifop-butyl were observed between X-77 surfactant and oil concentrate as herbicide additives in the greenhouse (Table 5). Quackgrass control with fluazifop-butyl in the greenhouse was lower than observed in the field in 1981 from equivalent rates (Table 2, 5). For example, fluazifop-butyl at 0.28 kg/ha with 0.5% X-77 surfactant provided 78% and 35% control of 9- to 13-cm tall quackgrass in the field and greenhouse, respectively. This may be due to reduced soil herbicidal activity in the greenhouse potting soil (7.8% organic matter). Annual grass control. Postemergence applications of sethoxydim, difenopenten, RO-l3 8895, CGA-82725, and NCI- 96683 at rates of 0.56 kg/ha provided 96% or greater control of 7- to 9-cm tall barnyardgrass and yellow foxtail in 1980 (Table 6). In addition, sethoxydim and RO-13 8895 were evaluated at rates of 0.14 kg/ha and were found to provide 91% or better control. NCI-96721 required a rate of 1.12 kg/ha to obtain 99% control. Diclofop-methyl provided 83% control at 1.12 kg/ha, the only rate tested (Table 6). 63 Table 5. Phytotoxicity on quackgrass in the greenhouse from fluazifop-butyl in combination with X-77, oil concentrate, acifluorfen, or bentazon.a Quackgrass controlg FluazifOp-butyl Rateb x-77c OCd Acie Benf (kg/ha) (%) 0 0e 0e 0e 0e 0.14 28d 25d 0.28 35cd SObC 43cd 40cd 0.56 75a 85a 68ab 68ab aMeans followed by a common letter are not significantly different at the 5% level of probability according to Duncan's multiple range test. bAll herbicide treatments were applied to 9- to l3-cm tall quackgrass. cX-77 surfactant was added to the spray mixture at 5% (v/v). dOil concentrate was addedtxathe spray mixture at 2.34 L/ha. eAcifluorfen was added to the spray mixture at 0.56 kg/ha. fBentazon and oil concentrate were added to the spray mixture at 0.84 kg/ha and 2.34 L/ha, respectively. gVisual evaluations were made 4 weeks after treatment. 64 Table 6. Barnyardgrass and yellow foxtail control from selective postemergence herbicides as affected by rate and herbicide combinations with acifluorfen and bentazon, 1980.6 Annual grass controlf Soybean injuryg Herbicide Rate 0Cc Acid Bene 0C Aci Ben (kg/ha) (%) Sethoxydim 0.14 100a 9e-h Sethoxydim 0.28 100a Slab 94ab 3gb 44a 24de Sethoxydim 0.56 100a 8e-h Difenopenten 0.56 96a 8e-h Difenopenten 1.12 96a l4c-h RO-l3 8895 0.14 91ab 4fgh RO-l3 8895 0.28 97a 56c 93ab 3fgh 46a 17c-g RO-l3-8895 0.56 100a lZd-h CGA-82725 0.28 95ab lld-h CGA-82725 0.56 99a ch-f NCI-96683 0.28 100a 20cde NCI-96683 0.56 100a 100a 29b 28bc NCI-96721 0.56 75bc lld-h NCI-96721 1.12 99a l4c-h Diclofop-methyl 1.12 83ab 21cde Uncultivated control 0d 0d 0d Oh Oh Oh aMeans within an evaluation followed by a common letter are not significantly different at the 5% level of probability according to Duncan's multiple range test. b soybeans (July 8, 1980). All treatments were applied to 7- to 9-cm tall grasses and two-trifoliolate cOil concentrate was added to the spray mixture at 2.34 L/ha. d Acifluorfen was added to the spray mixture at 0.56 kg/ha. aBentazon and oil concentrate were added to the spray mixture at 0.84 kg/ha and 2.34 L/ha, respectively. f Visual evaluations were made 3 weeks after treatment (August 1, 1980). 9Visual evaluations were made 10 days after treatment (July 18, 1980). 65 In 1981, early postemergence (EP) applications of sethoxydim, RO-13 8895, fluazifop-butyl, NCI-96683, CGA- 82725, and Dowco 453 at 0.14 kg/ha provided 90% or greater control of 4- to 6-cm tall barnyardgrass and giant foxtail (Table 7). DiclofOp-methyl at the same rate provided only limited control. The relative herbicidal activity of diclofop-methyl was significantly lower than each of the other herbicides examined. Late postemergence (LP) applications to l7- to 22-cm tall plants of 0.28 kg/ha of each of the herbicides tested except diclofop-methyl provided equivalent grass control as the same rate applied early (EP) (Table 7). This indicates considerable flexibility in the time of application for annual grass control with each of the herbicides tested except diclofop-methyl. Phytotoxicity on barnyardgrass in the greenhouse with fluazifop-butyl at rates of 0.14 and 0.28 kg/ha was reduced when the grass height at application was 13 to 15 cm compared to 3 to 6 cm (Table 8). However, greater phytotoxicity with fluazifop-butyl at rates of 0.07 to 0.28 was observed when application was made to 17- to 19-cm tall plants compared to 13- to 15-cm tall plants. This was especially apparent at the 0.07 kg/ha rate. This observation may be a result of greater spray retention by the larger plants. Herbicide combinations with acifluorfen and bentazon were examined with sethoxydim and RO-l3 8895 at 0.28 kg/ha in 1980. NCI-96683 at 0.56 kg/ha was also examined in combination with bentazon. The addition of acifluorfen to a Spray mixture (56 Table 7. Selective postemergence herbicides applied at several rates and plant heights and the resultant activity on barnyardgrass and giant foxtail, 1981. Annual ggass control Soybean injuryf Soybean yields Herbicide Rate EPC LPd 29 LP spb ch (kg/ha) (%) (kg/ha x 100) Sethoxydim 0.14 93ab lOdef 25ab Sethoxydim 0.28 90ab 97a 7def 7def 23ab 24ab RO-l3 8895 0.14 90ab 19bcd 23ab RO-l3 8895 0.28 96a 93ab 12def lOdef 27ab 25ab Fluazifop-butyl 0.14 95ab lOdef 25ab Fluazifop-butyl 0.28 92ab 84b 18de lOdef 24ab 27ab NCI-96683 0.14 98a 25bc 27ab NCI-96683 0.28 99a 100a 38a 30ab 27ab 27ab CGA-82725 0.14 96a 7def 31a CGA-82725 0.28 93ab 90ab 3h lOdef 23ab 25ab Dowco 453 0.07 94ab 25ab Dowco 453 0.14 98a lOdef 22ab Dowco 453 0.28 95ab 95ab l7cde 7def 23ab 30a Diclofop-methyl 0.14 35d Of 21ab Diclofop-methyl 0.28 57c 43d 5 ef 7def 21ab 20b Diclofop-methyl 0.56 100a 27abc 23ab Uncultivated control 0e 0e 0f 0f 21ab 21ab Hand weeded control 100a 100a 0f 0f 7c 7c aMeans within an evaluation followed by a common letter are not significantly different at the 5% level of probability according to Duncan's multiple range test. b All herbicide treatments except those involving fluazifop-butyl included oil concentrate at 2.34 L/ha. Fluazifop-butyl was applied with X-77 at 0.5% (v/v). cEarly postemergence (EP) treatments were applied to 7- to 9-cm grasses and two- to three- trifoliolate soybeans (June 19, d 1981). Late postemergence (LP) treatments were applied to 17- to 22-cm grasses and five- to six- trifoliolate soybeans (July 1, 1981). 6Visual evaluations were made 3 weeks after the late (LP) treatments were applied (July 21, 1981). f Visual evaluations were made 7 days after treatment. 67 Table 8. Phototoxicity on barnyardgrass in the greenhouse from fluazifop-butyl applied at several rates and plant heights. Barnyardgrass controld Fluazifop-butyl rateb 4-6 cmC 8-10 cm 13-15 cm 17-19 cm (kg/ha) * (%) 0 0f 0f 0f 0f 0.07 188 l4e 186 40d 0.14 78b 63C 40d 63C 0.28 94a 87ab 65C 78b 0.56 930 aMeans followed by a common letter are not significantly different at the 5% level of probability according to Duncan's multiple range test. bAll herbicide treatments included oil concentrate at 2.34 L/ha. cBarnyardgrass height at the time of application. dVisual evaluations were made 2 weeks after treatment. 68 with RO-l3 8895 reduced 4- to 6-cm tall barnyardgrass and yellow foxtail control from 99 to 56% (Table 6). No other antagonisms were observed in 1980. In 1981, no reduction in control of 4- to 6-cm tall barnyardgrass and giant foxtail was observed when either acifluorfen or bentazon was added to 0.28 kg/ha rates of each of the herbicides tested except diclofop-methyl (Table 9). The addition of acifluorfen or bentazon to spray mixtures with diclofop-methyl at 0.28 kg/ha resulted in a 21 and 51% reduction in grass control, respectively (Table 9). This antagonistic interaction with bentazon has been reported by several researchers (3,4,14,20). Addition of bentazon to spray mixtures with 0.14 kg/ha of fluazifop-butyl significantly reduced phytotoxicity on 4- to 6-cm tall barnyardgrass in the greenhouse. However, when the rate of fluazifop-butyl was increased to 0.28 kg/ha no reduction in control was observed. This observation is consistent with the results on quackgrass control in 1981 (Table 4) and further demonstrates that antagonistic herbicide interactions may be overcome, at least in part, by increasing the rate of the grass herbicide. This may also explain why no antagonistic interactions were observed on barnyardgrass and giant foxtail in 1981 (Table 9). Phytotoxicity on 4- to 6-cm tall barnyardgrass in the greenhouse with 0.07 kg/ha of fluazifop-butyl was increased by the addition of acifluorfen to the spray mixture (Table 10). 69 .uceeumeuu Heumm when 5 ends ewe: mcoflumsam>e Hesmfl>m .Aaema .HN wasee uceEueeuu ueume exee3 q eves euez ucoHumsHm>e Hesuw>w .>He>auoemmeu .ec\A qm.~ can mc\mx ve.e um ensust heumm ecu ou pence euez eumuuceocoo Hwo one conuceme .mc\mx em.e um ensuxwe aeumm ecu ou pence mm: cemuosamwom n .mc\n vm.m um enquME henna ecu ou mecca um3 eueuuceocoo uwou .xumau .mu ensue memenaom eumHOAHoMuuu ueeucu ou io3u one memmeum Hamu scum ou uh ou neuflmdm euez musesumeuu eCAOficuec HaeH mm ecu um uceueumflc xauceOflwwcmflm uoc eum Heuuea COEEoo m an pesoHHow cofiumsam>e cm cacuws annexe on be on we we we we we we douucoo cepees one: cmam ceHN cmHN go we Me meea meeH neeH Houunoo peue>wuasoca ceH cmvm cuam even 0me wcm eem me ohm e~.e HacueEIQOMOHowo new ceeN comm uehw nee cmuha coca name came eN.e mmq ooson comm cem~ comm enmm ans «m cube nee comm e~.e mwhmeicoo new neN chm one case even see cuee nee em.e meeemiauz comm new covm oee cub emea cuem nee comm e~.e HausQIQOMANesHm new comm new even ones wcmNH cuem cme comm e~.e meme maiom new new cem~ meem open acme comm comm seem eN.e Euohxocuem lilacs x uc\mxell awe .mcxmxe cem Mod 00 cem five 00 ecem cwoc coo euem netwowcue: mpaewx :mecaom lNusflcfi cmemxom Houucoo mmmum Hmsc:< w w m.HeeH .cmec>0m can .Humuxom undue .mmmumcum>cumc co aufi>auoe uceuasmeu ecu can mepflowcuec wanna use «meacmouc eonemuefieumom e>wuoeaeu mo mGOAumcchou .m eacea 70 Table 10. Phytotoxicity ontarnyardgrass in the greenhouse from fluazifop-butyl in combination with X-77, oil concentrate, acifluorfen, or bentazona. Barnyardgrass controlg Herbicided Rate X-77C OCd Acie Benf (kg/ha) (%) Fluazifop-butyl 0.07 28e 18ef 77cd 18ef Fluazifop-butyl 0.14 87abc 78c 86bc 66d Fluazifop-butyl 0.28 99a 94ab 94ab 92ab None 73cd 8fg Untreated control 09 Og 09 0g aMeans followed by a common letter are not significantly different at the 5% level of probability according to Duncan's multiple range test. bAll herbicide treatments were applied to barnyardgrass plants 7 to 9 cm in height. CX-77 surfactant was added to the Spray mixture at 5% (v/v). dOil concentrate was added to the spray mixture at 2.34 L/ha. eAcifluorfen was added to the spray mixture at 0.56 kg/ha. fBentazon and oil concentrate were added to the spray mixture at 0.84 kg/ha and 2.34 L/ha, respectively. gVisual evaluations were made 2 weeks after treatment. 71 This is explained by the observation that acifluorfen provided 73% barnyardgrass control when applied alone (Table 10). Similar to results on quackgrass control in the greenhouse, no significant difference in phytotoxicity on barnyardgrass with fluazifop-butyl was observed between x-77 surfactant and oil concentrate as additives (Table 5, 10). In both 1980 and 1981, addition of acifluorfen to herbicide mixtures with each grass herbicide tested resulted in signi- ficantly greater soybean injury (Tables 6, 9). In addition, herbicide combinations with bentazon in 1981 resulted in significantly greater soybean injury with all herbicides examined except fluazifop-butyl and Dow 453 (Table 9). Soybean injury was observed from herbicide combinations with acifluorfen in 1981; however, this injury did not result in any reduction in yield as compared to the hand weeded control and all treatments provided significantly greater soybean yields than the uncultivated control (Table 9). This observation and similar results in the 1980 quackgrass control study (Table 1) indicate that soybeans have a high capacity to compensate for damaged tissue from foliar applications of these herbicides. These results also sug- gest that complete eradication of annual grasses or quackgrass may not be necessary to eliminate interference with the soybean crop. However, complete eradication may be important to eliminate seed production with annual grasses and to eliminate quackgrass regrowth in subsequent cropping systems. 72 Soil activity and persistence studies. Herbicidal activity and persistence of activity was observed on germinating barnyardgrass seeds from soil applications of fluazifop-butyl (Figure 1). This observation is con- sistent with reports by Plowman et al. (13). Soil application of 0.07 kg/ha of fluazifop-butyl reduced barnyardgrass dry matter accumulation by 43% compared to the untreated control. FluazifOp-butyl applied to the soil at rates of 0.28 kg/ha or higher, resulted in 90% or greater reduction in barnyard- grass dry matter accumulation. Results also indicate persistence of activity from fluazifop-butyl in the soil. Application rates of 0.56 kg/ha provided 90% or greater control for 10 days after treatment (DAT) with no activity apparent at 30 DAT. Fluazifop-butyl applied to the soil at rates of 1.12 and 2.24 kg/ha provided 90% or greater control of germinating barnyardgrass seeds for 20 DAT and 30 DAT, respectively. No herbicidal activity from soil applications of fluazifop-butyl at rates of 2.24 kg/ha or lower was apparent 50 DAT (Figure 1). Soil herbicidal activity was also examined on established barnyardgrass plants. The addition of vermiculite to the soil surface prior to herbicide application significantly reduced control of 4- to 6-cm tall barnyardgrass with fluazifop-butyl at rates of 0.07 and 0.14 kg/ha (Table 11). This response occurred under plant populations of both 3 plants/pot and 50 plants/pot. This indicates that herbi- cidal activity in the soil may contribute to barnyardgrass 73 Figure l. Herbicidal activity and persistence of fluazifop- -butyl following application to a sandy loam soil. The indicator was barnyardgrass planted and harvested at 10 day intervals. Herbicidal activity is reported as a reduction in dry matter accumulation compared to the untreated control. 74 hzuihiuch muhh< m>0m mu._.h_< mBDO: 9v 0" 0383A0338 :IO NOIlVOO'ISNVIM. % Figure 2. 92 Translocation of 14C following application of fluazifop-butyl to quackgrass and soybeans. 14 C- 93 . hzuEh0m a— 3." GBHSAOOBH J0 NOILVOO'ISNVIJ. % 94 basipetal translocation in both Species 6 h after treatment (Figures 3, 4). After 144 h the radiolabel was distributed throughout all plant parts of both species, including the adjacent Shoot in quackgrass. Radioautographs also indi- cate accumulation of 14C in meristematic areas of both plants (Figures 3, 4). These data indicate that absorption and translocation are not selectivity mechanism for fluazifop- butyl between quackgrass and soybeans. 14 14 Recovery of C following application of C-fluazifOp- butyl decreased over time in both species (Figure 5). Recovery of applied 14C 144 h after treatment was signifi- cantly greater:hisoybeans compared to quackgrass with 79.2% and 66.2% recovery, respectively. This observation may be related to the more rapid rate of absorption by soybeans (Figure l) . Comparison of quackgrass growth stages. In the greenhouse, quackgrass control with 0.56 kg/ha fluazifOp- butyl was significantly greater when treatments were applied to plants in the two- to three-leaf stage compared to plants in the five- to Six-leaf stage (Table l). Quackgrass plants 14 treated with C-fluazifop-butyl at the two- to three-leaf 14c 144 h after stage translocated 12.4% of the applied treatment compared to 10.0% translocation in plants at the five- to six-leaf stage; however, this difference was not significant (Table 2). Significantly more 14C was removed in the leaf wash from treated leaves of the plants at the five- to six-leaf stage. This indicates a difference in Figure 3. 95 Translocation and distribution of l4C-fluazifop- butyl in quackgrass. Plant and corresponding radioautograph following harvest 6 h after treatment (A) and 144 h after treatment (B). Plant left, radioautograph right. The treated portion of the treated leaf is marked with an arrow. 97 Translocation and distribution of l4C-fluazifop- butyl in soybeans. Plant and corresponding radioautograph following harvest 6 h after treatment (A) and 144 h after treatment (B). Plant left, radioautograph right. The treated portion of the treated leaf is marked with an arrow. Figure 4. 98 99 Figure 5. Recovery of 14C following application of 14C- fluazifop-butyl to quackgrass and soybeans. 100 #52235. mute. £50: 3.. 3 o mm<¢0¥u<30 1 0e mzfigom O." 03l'lddV :IO AHSAOOEH % 101 Table l. The effect of time of treatment and sequential applications on quackgrass phytotoxicity with fluazifop-butyl in the greenhouse 4 weeks after treatment.a Quackgrass control Fluazifop-butyl rateb EPC LP EP + LP (kg/ha) (%) 0 0f 0f 0f 0.14 28e 25e 0.28 35de 35de 40de 0.56 75ab 53cd 63bc 1.12 80ab 65bc 88a aMeans followed by a common letter are not significantly different at the 5% level of probability according to Duncan's multiple range test. bAll herbicide treatments included X-77 surfactant at 0.5% (v/v). cEarly postemergence (EP) and late postemergence (LP) treatments were applied to quackgrass plants in the two- to three-leaf and five- to six-leaf stage, respectively. 102 the characteristics of the cuticle with different maturities of quackgrass. No differences in recovery or translocation were observed (Table 2). Radioautographs of treated plants suggest that, although total translocation was similar, distribution throughout the plant was more extensive in plants in the two- to three-leaf stage with much of the translocated 14 C in the plants at the five- to Six-leaf stage remaining in the proximal untreated portion of the treated leaf (Figure 6). These differences may partially explain the loss of control with fluazifop-butyl observed in the greenhouse when applied to plants at the five- to six-leaf stage. Effect of temperature. Significantly greater quackgrass phytotoxicity with 0.28 kg/ha fluazifop-butyl was observed with plants under 30 C compared to 20 C (Table 3). However, this response was not observed when the application rate was increased to 0.56 kg/ha. With quackgrass plants treated with l4C-fluazifop-butyl, no significant difference in trans- location was observed bewteen 20 C and 30 C (Table 2). However, absorption was significantly greater at 30 C with 71.4% absorption of the applied l4C compared to 45.3% absorption at 20 C. In addition, leaf washes removed more than six times more 14 C from plants at 20 C compared to 30 C. No quantitative differences in translocation or recovery were observed (Table 2). Although no quantitative difference in total translocation occurred, radioautographs indicate more extensive distribution of 14C in plants under 103 Table 2. The effect of plant growth stage, temperature, light, and moisture stress on absorption, translocation, and recovery of l4C-fluazifop- butyl in quackgrass 144 h after treatment.a % of Applied l4C Leaf Variable Recovered wash Absorbed Translocated (%) Growth Stage 5 to 6 leaf 68.8a 9.3a 59.5a 10.0a 2 to 3 leaf 71.8a 4.4b 67.4a 12.4a Temperature 20C 74.8a 29.5a 45.3b 8.8a 30C 75.7a 4.3b 71.4a 8.4a Illuminanceb Light 73.4a 6.1a 67.3a 17.9a Shade 67.9a 6.0a 61.9a 14.1b Moisture Stressc Moist soil 73.7a 3.0a 70.7a 18.4a Dry soil 68.1a 4.9a 63.2a 14.3a aMeans within a variable and column followed by a common letter are not significantly different at the 5% level of probability. bIrradiance in light and shade was ZBOUE-m-2°S 53pE-m'2-S'1, respectively. -1 and cSoil moisture was field capacity [21% (w/w)] for moist soil and 6 to 10% (w/w) for dry soil. Figure 6. 104 The influence of quackgrass growth stage on trans- location and distribution of l4C-fluazifop-butyl in quackgrass. Plant and corresponding radio- autograph of quackgrass plants in the two- to three-leaf stage (A) and the five- to Six-leaf stage (B). Plant left, radioautograph right. The treated portion of the treated leaf is marked with an arrow. 105 \ 106 .aae>fiuoemmeu . 0. 8.0:mm 0:0 0. 5.0:eem 003 000cm 0:0 ucmaa cu eoc0w00uuH .eusumuoe A3\3e wed 0:0 0 cee3uec oecu0ucw0e 003 Hu00 aha M .HA3\3V waa. xuuo0m0o oflewm u0e: H0 u0 oecfi0ucw0s 003 Huom umuoze .0c\A vm.m u0 ensuxue >0um0 ecu ou 00000 003 eu0uuceocoo Hwo 0 .A>\>e wm.e u0 eusuxua >0u00 ecu ou 00000 003 uc0uommusm hhlxo HI NI HI NI 0 .u0eu emc0u eaduuase 0.00ocsa ou ecuouoooo auuawc0coum mo He>eH am ecu u0 uceueuwuo xauc00www00u0 uoc eu0 ueuuea 005500 0 kc 0e30HH00 uouo0m H0uceacouw>ce :0 cacuu3 000020 ocmv 0ve 00mm c0vm 0eea 0mm 0em c0ee 0mm 0mm em.e 0H~ 00H 0ma poem Dav comp ocmm oem own One e~.e ee 0e 0e ee 0e 0e 0e 0e 0e to e 2: 8&9: qum and H000 umuoz uqum and euuom umuoz 000cm ucmuo 000cm ucmuo oom ecu mumz 0.0.0 unhnx 000cm cucmfin ensu0uemEeB Houucoo 000mmx0050 0.u:eEueeuu Heuu0 03003 v H>u301000u00sam cufl3 >uu0uxouou>cm 000umx00sv co 00euu0 eusueuos 0:0 .ucmua .eusuouemeeu mo eocesumcw eca .m eHc0a 107 30 C compared to 20 C (Figure 7). Increased absorption and more extensive distribution in plants under 30 C com- pared to 20 C may partially explain the lower phytotoxicity of fluazifop-butyl on quackgrass plants exposed to 20 C. Effect of light. No Significant difference in herbicidal activity from fluazifop-butyl at 0.28 kg/ha was observed between quackgrass plants maintained in constant shade or full light (Table 3). However, greatest control was observed on plants exposed to shade for 48 h prior to treatment and to full light following treatment. In addi- tion, early evaluations of treated plants indicate that phytotoxicity occurred more rapidly with plants exposed to shade before treatment and full light after treatment. The effect of light was overcome by increasing the rate of fluazifop-butyl to 0.56 kg/ha (Table 3). Translocation of 14C in quackgrass following application of l4C-fluazifop- butyl was significantly greater under full light compared to shade (Table 2). Plants exposed to full light translocated 17.9% of the applied l4C compared to 14.1% translocation under shaded conditions. No significant differences in absorption or recovery were observed (Table 2). Radioauto- graphs of treated plants indicate no difference in distribution of 14C between plants in full light and plants in shade. l4C-fluazifop- (Figure 8). Data suggest that translocation of butyl is influenced by photosynthate movement in the phloem. Reduced translocation under lower irradiance may influence herbicidal activity of fluazifop-butyl under certain conditions. Figure 7. 108 The influence of tem erature on translocation and distribution of 4C-fluazifop-butyl. Plant and corresponding radioautograph of quackgrass maintained at 20 C (A) and 30 C (B). Plant left, radioautograph right. The treated portion of the treated leaf is marked with an arrow. 109 a. ' e. ‘G-ng‘4‘3 El , 7' .9 Figure 8. 110 The influence of irradiance on translocation and distribution of l4C-fluazifop-butyl in quackgrass. Plant and corresponding radioautograph of quack- grass maintained under light irradiance of 280qum'2-s‘1 (A) and 53uE-m"2-s'l (B). Plant left, radioautograph right. The treated portion of the treated leaf is marked with an arrow. 111 112 Effect of moisture stress. Herbicidal activity of fluazifop-butyl at 0.56 kg/ha was significantly greater when application was made to plants maintained under adequate moisture compared to plants under moisture stress (Table 3). This observation agrees with findings on johnsongrass reported by Ready and Wilkerson (11). This response was observed when either X-77 at 0.5% (v/v) or oil concentrate at 2.34 L/ha were included in the spray mixture. No significant difference in control with fluazifop-butyl was observed between X-77 and oil concentrate as spray additives (Table 3). Translocation of 14C in quackgrass following application of 14 C-fluazifop-butyl was 18.4% in plants under adequate moisture compared to 14.3% in plants under moisture stress; however, this difference was not signifi- cant (Table 2). No significant differences in absorption or recovery were observed. However, radioautographs of treated plants suggest that more extensive distribution 14 of C occurred in plants grown under adequate moisture (Figure 9). In another study, absorption of 14C 144 h after treatment was significantly greater when a foliar application prior to treatment with the radiolabel included oil concentrate at 2.34 L/ha compared to 0.5% (v/v) X-77 surfactant as is shown in Table l of the appendix. No significant differences in absorption or translocation were observed with spray mixtures of fluazifop-butyl with bentazon [3-isopropy1-1H- 2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] or acifluorfen [sodium 5-2-chloro-4-(trifluoromethyl)-phenxoy-2-nitrobenzoate]. . ""3“? Figure 9. 113 The influence of soil moisture on translocation and distribution of 14C-f1uazifop-butyl. Plant and corresponding radioautograph of quackgrass maintained at 6 to 10% (w/w) soil moisture (A) and 21% (w/w) soil moisture (B). Plant left, radioautograph right. The treated portion of the treated leaf is marked with an arrow. 115 Herbicidal activity of fluazifop-butyl on quackgrass is influenced by several variables including plant growth stage, temperature, light, and moisture stress. The effect of these variables on absorption, translocation and dis- tribution of fluazifop-butyl in quackgrass may partially explain the influence of these variables on herbicidal activity. 10. 11. 12. 116 LITERATURE CITED Boldt, P. F. and A. R. Putnam. 1980. Selectivity mechanisms for foliar application of diclofop-methyl. I Retention, absorption, translocation and volatility. Weed Sci. 28:474-477. Campbell, J. R. and D. Penner. 1981. Absorption and translocation of BAS-9052 OH (2-[1-(ethoxyimino)-butyl]- 5-[2-(ethylthio)-propyl]-3-hydroxy-2-cyclohexen-l-one). Abstr. Weed Sci. Soc. Am., p. 13. Colby, S. R., J. R. Bone and A. A. Akhavein. 1982. PP009,:13elective herbicide for control of perennial and annual grasses. Abstr. Weed Sci. Soc. Am., p. l4-15. Crafts, A. S. and S. Yamaguchi. 1964. The autoradio- graphy of plant materials. California Agric. Exp. Sta. Manual 35. 143 pp. Hoagland, D. R. and D. I. Arnon. 1950. The water culture method for growing plants without soil. California Agric. Exp. Sta. Circ. 347. 32 pp. Holm, L. G., D. L. Plucknett, J. V. Poncho, and J. P. Herberger. 1977. The World's Worst Weeds. University Press of Hawaii, Honolulu, Hawaii. 609 pp. Kells, J. J. and C. E. Rieck. 1979. Effect of illuminance and time on accumulation of glyphosate in johnsongrass. Weed Sci. 27:235-237. Linscott, D. L. 1970. The ten worst weeds in field crops. Quackgrass. Crops and Soils 23:-8-9. McWhorter, C. G. 1981. The effect of temperature and relative humidity on translocation of 14C-metriflufen in johnsongrass (Sor hum halepense) and soybean (Glycine max). Weed Sci. 27:42-47. Plowman, R. E., W. C. Stonebridge and J. N. Hawtree. 1980. F1uazifop-butyl--a new selective herbicide for the control of annual and perennial grass weeds. Proc. British Weed Control Conf. 17:29-37. Ready III, E. L. and J. Wilkerson. 1982. Postemergence control of rhizome johnsongrass [Sorghum halepense (L.) Pers.] with PP009 as effected by drought stress. Abstr. Weed Sci. Soc. Am., p. 15. Sprankle, P., W. F. Meggitt, and D. Penner. 1975. Absorption, action, and translocation of glyphosate. Weed Sci. 23:235-240. CHAPTER 4 SUMMARY AND CONCLUSIONS Studies were conducted in the field to evaluate the efficacy of several selective postemergence grass herbicides in soybeans and to examine factors influencing grass control with these herbicides. Greenhouse and laboratory studies were conducted to examine factors affecting absorption, translocation, and herbicidal activity of fluazifop-butyl. Several herbicides were found to provide excellent control of quackgrass and annual grasses with little injury to soybeans. In all cases the rate necessary for annual grass control was less than for quackgrass. For control of quackgrass the time of application was an important factor with each of the compounds tested. In 1980, late treatments applied to 16- to 22-cm tall quackgrass provided greater midseason quackgrass control and regrowth control than early treatments applied to 7- to 13-cm tall plants with most of the herbicides tested. In 1981, no differences in control were observed between early and late treatments; however, quackgrass regrowth control the following spring was greater from early treatments with most of the herbicides tested. This indicates less translocation to the perennial 117 118 tissue of the larger plants. Data indicate that a window of maximum control exists in terms of quackgrass growth stage. The time of application was more critical for certain herbicides than others. For example, quackgrass control with RO-l3 8895 appeared to be the most sensitive to plant growth stage while control with NCI-96683 and Dowco 453 was influenced much less by plant growth stage. Soil herbicidal activity may explain in part the reduced influence of plant growth stage on quackgrass control with NCI-96683 and Dowco 453. Sequential applications of each of the herbicides tested provided equal or greater quack- grass control and regrowth control than single applications of the same total rate regardless of the time of application. From a practical standpoint the optimum time of application may not be a critical issue since it is likely that these herbicides will be applied in sequential applications for quackgrass control. Plant growth stage was much less critical for annual grass control in the field compared to quackgrass. Herbicide antagonisms on annual grasses were consistently observed only with diclofop-methyl. Quackgrass control with several postemergence grass herbicides was significantly reduced when acifluorfen or bentazon was added to the spray mixture. The intensity of these antagonisms varied between compounds and could be overcome in part by increasing the rate of the grass herbicide. Greenhouse and laboratory data indicate that the antagonism between fluazifop-butyl and bentazon is not related to absorption or translocation 119 of fluazifop-butyl. An understanding of these antagonisms by herbicide applicators is important in order to avoid loss of control with certain herbicide combinations. Herbicide injury to soybeans from each of the compounds tested was minimal with the greatest injury observed with NCI-96683 and NCI-96721. Injury was always significantly greater when acifluorfen was included in the spray mixture. However, herbicide injury was not persistent and plants were able to recover. Data indicate that herbicide injury did not result in a Significant yield reduction. Yield data also indicate that complete eradication of grasses may not be necessary in order to eliminate competition with the crop. Greenhouse studies with fluazifop-butyl indicate herbicidal activity on barnyardgrass and quackgrass from applications to the soil. Herbicidal activity from fluazifop- butyl applied to the soil at 1.12 kg/ha persisted for 30 days after treatment. Soil herbicidal activity contributed to control of 4- to 6-cm tall barnyardgrass from foliar applications of fluazifop-butyl in the greenhouse. Activity and persistence of fluazifop-butyl in the soil may be an important factor in effective control, especially in control of grasses that germinate after treatment. Greenhouse and laboratory experiments with 14 C-fluazifop- butyl indicate that the herbicide is absorbed, translocated, and distributed throughout the plant in both quackgrass and soybeans. Absorption occurred more rapidly in soybeans, a 120 tolerant species. These results indicate that absorption and translocation are not selectivity mechanisms for fluazifop-butyl. Several environmental factors affected absorption, translocation of herbicidal activity of fluazifop-butyl in the greenhouse. Data suggest that greater herbicidal activity on quackgrass plants at the two- to three-leaf stage compared to those at the five- to six-leaf stage may be related to greater absorption and distribution in the younger plants. Greater herbicidal activity was observed with quackgrass plants maintained at 30 C compared to 20 C. This may be related to much greater absorption and more complete distribution of the radiolabel at 30 C compared to 20 C. Significantly greater translocation of 14C 14 following application of C-fluazifop-butyl occurred in quackgrass plants exposed to light irradiance of 28011E-m-2-s-l compared to 53uE-m-2-s-1. This suggests that light may influence quackgrass control in the field with fluazifop- butyl, especially when minimal rates are used. Herbicidal activity of fluazifOp-butyl was significantly reduced with plants grown under moisture stress. However, no significant differences in absorption or translocation were observed. The chemistry of herbicides examined in this study offer some interesting comparisons. Each of the herbicides with known chemistry except sethoxydim are either diphenyl- ether structures or are closely related to diphenyl-ethers. General herbicidal activity of each of the compounds is 121 similar. Diclofop-methyl, metriflufen, difenopenten, and RO-13 8895 are diphenyl-ethers. Of these four herbicides, diclofop-methyl is the only compound that lacks herbicidal activity on quackgrass. It is also the only compound that does not have a trifluoromethyl group in its structure. In addition development of each of the four herbicides except diclofop-methyl has been discontinued by the respective companies. CGA 82725, fluazifop-butyl, and Dowco 453 are each (2-pyrindinyl)oxy-phenoxy-propanoate herbicides. Of these three herbicides, CGA-82725 has much less herbi- cidal activity on quackgrass and is the only herbicide of this group which does not have a trifluoromethyl group in its structure. The only compound evaluated with known chemistry which has herbicidal activity on quackgrass and does not contain a trifluoromethyl group is sethoxydim. In conclusion, selective postemergence grass control in broadleaved crops represents a new concept in chemical weed control. Herbicides in this class are expected to provide a valuable mechanism for quackgrass control in broadleaved crOps such as soybeans. In addition, these herbicides provide considerable flexibility in postemer- gence control of annual grasses. The role that each of these herbicides will fill in a weed control program will be dependent upon several factors including the cropping rotation, the spectrum of weeds present, and the cost of the herbicides to the producer. APPENDIX 122 Table 1. Absorption, translocation, and recovery of l4C-fluazifOp-butyl in quackgrass 144 h after treatment as affected by pretreatment with herbicide additives and herbicide combinations. % of applied l4C Herbicide Pretreatment Recovered Leaf wash Absorbed Translocated - (%) Fluazifop-butyl+ X-77 7l.8c 4.4b 67.40 12.4a Fluazifop-butyl+ O.C. 85.5a 8.6a 76.9a 12.8a Fluazifop-butyl+ acifluorfen 72.7c 10.0a 62.7bc 10.8a F1uazifop-butyl+ bentazon+O.C. 79.7b 5.9b 73.8ab 12.8a aMeans within a column followed by a common letter are not significantly different at the 5% level of probability according to Duncan's multiple range test. bFluazifop-butyl, X-77 surfactant, oil concentrate (0C), acifluorfen, and bentazon were applied at 0.56 kg/ha, 0.5% (v/v), 2.34 L/ha, 0.56 kg/ha, and 0.84 kg/ha, respectively. "11111111171111.1113