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(“L {-‘x. has been accepted towards fulfillment of the requirements for fl’fl 3; 1‘3 f' 3- degree in #16:.) r fit u ( f 'J ft: Major professor Date [9/ 2(0! (78% 0-7639 MS U is an Affirmative Action/Equal Opportunity Institution MSU LIBRARIES -_ RETURNING 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. INFLUENCE OF ENVIRONMENTAL AND APPLICATION FACTORS ON THE GRAMINICIDAL ACTIVITY OF FLUAZIFOP-BUTYL By Reid J. Smeda A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTERS OF SCIENCE Department of Horticulture I984 ABSTRACT INFLUENCE OF ENVIRONMENTAL AND APPLICATION FACTORS ON THE GRAMINICIDAL ACTIVITY OF FLUAZIFOP-BUTYL By Reid J. Smeda Field studies with fluazifop-butyl ((:)-butyl 2- [4-(I5- ltrifluoromethyl)-2-pyridinyl] oxy) phenoxy] propanoate) indicated a differential response among annual grass species and small grains, with decreased sensitivity with increasing plant age. A general dscending order of tolerance was: green foxtail > large crabgrass > yellow foxtail > giant foxtail 3_Japaneselnillet. Oats and rye were more tolerant than wheat and sorghum. Increasing ambient temperature from l8 to 30 C reduced toxicity on green foxtail, but not Japaneselnillet. Although activity was affected by time of day of application, no consistent pattern was observed. Simulated rainfall within two hours of herbicide application reduced control of green foxtail and Japanese millet. Toxicity of fluazifop- butyl to large crabgrass in the greenhouse was significantly increased as carrier volumes were reduced from 374 to 47 L/ha, or as adjuvant concentrations were increased from 0.625 to 5% v/v. Reduced activity from less than optimal carrier volumes and adjuvant concentrations or from rainfall after application, were generally alleviated by increasing the herbicide rates. ACKNOWLEDGEMENTS This research could not have been done without the help of many student workers and the technical assistance of Mr. Bill Chase. Thank you for your patience through many hours of "weed harvests" and other tedious work. Thanks also to my fellow graduate students who added encouragement and constructive criticism, making sure that I would finish this project, instead of setting up that 998th experiment. Appreciation is given to Drs. James J. Kells and Bernard H. Zandstra for serving on my guidance committee. Special thanks to Dr. Alan R. Putnam for his guidance, time and knowledge, which will benefit me throughout my career. To Jackie, many thanks Your clerical assistance prevented many gray hairs and saved months of my life. To my wife, Corinne, words cannot express my gratitude for your devotion and encouragement throughout this project. Finally, and most importantly, to Him who strengthens me, may this work praise Your Name. ii TABLE OF CONTENTS Page INTRODUCTION ............................ l CHAPTER I - REVIEW OF LITERATURE .................. 3 Overview of Postemergence Graminicides ............. 3 Tolerant Species and Potential Uses ............. 4 Annual Grass Susceptibility ................. l2 Perennial Grass Susceptibility ................ 16 Environmental Factors Influencing Efficacy ........... l9 Application Factors Affecting Efficacy ............. 22 Spray Volume ......................... 22 Adjuvants .......................... 24 Herbicide Interactions .................... 26 Herbicidal Activity in Soil ................... 30 Fate In Plants ......................... 35 Absorption .......................... 35 Translocation ........................ 38 Metabolism .......................... 4] Mode of Action ........................ 44 LITERATURE CITED .......................... 47 Page CHAPTER 2 - RESPONSE OF SELECTED ANNUAL GRASSES AND CEREAL CROPS T0 FOLIAR APPLICATIONS OF FLUAZIFOP-BUTYL ............. 73 ABSTRACT .............................. 73 INTRODUCTION ............................ 74 MATERIALS AND METHODS ....................... 75 Greenhouse Investigations .................... 75 Field Investigations ...................... 76 General Procedures for Annual Grass Studies ......... 76 Grass Study, 1983 ...................... 77 Grass Study, l984 ...................... 80 Grain Crop Study ....................... 80 RESULTS AND DISCUSSION ....................... 8] Greenhouse Investigations .................... 8l Field Investigations ...................... 84 Grass Study, 1983 ...................... 84 Grass Study, 1984 ...................... 90 Grain Crop Study ....................... 96 LITERATURE CITED .......................... 102 CHAPTER 3 - THE INFLUENCE OF TEMPERATURE, RAINFALL, AND TIME OF DAY ON THE EFFICACY OF FLUAZIFOP-BUTYL ............. l06 ABSTRACT .............................. 106 INTRODUCTION ............................ l07 MATERIALS AND METHODS ....................... 108 General Greenhouse Procedures .................. l08 Effect of Temperature ...................... lO9 Effect of Time of Application .................. llO Effect of Rainfall ....................... lll iv Page RESULTS AND DISCUSSION ....................... 111 Effect of Temperature ...................... 111 Effect of Time of Application .................. 118 Effect of Rainfall ....................... 122 LITERATURE CITED .......................... 127 CHAPTER 4 - EFFECT OF CARRIER VOLUME AND ADJUVANT CONCENTRATION ON THE TOXICITY OF FLUAZIFOP-BUTYL ................. 130 ABSTRACT .............................. 130 INTRODUCTION ............................ 131 MATERIALS AND METHODS ....................... 133 Field Investigations ...................... 133 General Procedures ...................... 133 1982 Field Studies .................... 133 1983 Field Studies .................... 134 Greenhouse Investigations .................... 134 General Procedures ...................... 134 Adjuvant Study ........................ 135 Spray Volume and Adjuvant Study ............... 135 RESULTS AND DISCUSSION ....................... 136 Field Investigations ...................... 136 1982 Field Study ....................... 136 1983 Field Study ....................... 136 Greenhouse Investigations .................... 141 Adjuvant Study ........................ 141 Spray Volume and Adjuvant Study ............... 145 General Discussion ...................... 145 LITERATURE CITED .......................... 151 Table LIST OF TABLES CHAPTER 1 .Page General characteristics of selected postemergence graminicides ....................... 5 Physical properties of selected postemergence grass herbicides ........................ 6 Chemical rates necessary for adequate control (>80%) of various annual and perennial grasses. Only selected graminicides currently labelled or under later stages of development are included. At the time of application, grasses are assumed to be actively growing and not under environmental stresses .................. 13 Reported antagonism from tank-mixes of various broadleaf and grass herbicides .............. 27 Common name and chemical name of various broadleaf herbicides ........................ 28 CHAPTER 2 Climatic conditions and dates of herbicide application for the five species in the 1983 annual grass study . . . 78 Climatic conditions and dates of herbicide application for the five species in the 1984 annual grass study . . . 79 vi Table Trend comparisons for grass response to increasing fluazifop-butyl rate for each growth stage ........ 89 Average visual injury rating (0 = no effect, 10 = complete kill) for 1983 and 1984 grass species averaged over fluazifop-butyl rates and grwoth stages . . 93 Correlation of dry weight (as a % of control) and visual injury ratings for 5 grass species in 1983 and 1984 ......................... 95 Trend comparison for grass response to increasing fluazifop-butyl rate for each growth stage ........ 99 Correlation of dry weight (as a % of control) and visual injury ratings for 4 grass species ........ 101 CHAPTER 3 Analysis of variance and trend comparisons for green foxtail and Japanese millet response to increasing fluazifop-butyl rates and air temperatures ........ 116 Analysis of variance and trend comparison for green foxtail and Japanese millet response to increasing fluazifop-butyl rates .................. 121 CHAPTER 4 Analysis of variance and trend comparisons for large crabgrass response to increasing fluazifop-butyl rates and adjuvant concentrations ................ 144 vii Table Effect of spray volume and adjuvant concentration on the response of large crabgrass to fluazifop-butyl . . . . 146 Analysis of variance and trend comparison for large crabgrass response to increasing adjuvant concentrations and spray volumes ..................... 147 viii Figure LIST OF FIGURES CHAPTER 1 ngg Common name (if available), chemical name, and molecular structure of selected postemergence grass herbicides. . . . 7 Proposed metabolism of diclofop-methyl in wheat and wild oats (186) ...................... 42 CHAPTER 2 Response of barnyardgrass (Bygr) and Japanese millet (Jami) to fluazifop-butyl ................. 82 Response of green foxtail (A), large crabgrass (B), yellow foxtail (C), giant foxtail (D), and Japanese millet (E) to fluazifop-butyl in 1983 and 1984 ........................... 85 Response of oats (A), rye (B), wheat (C), and sorghum (D) to fluazifop-butyl, l7 and 28 days after planting (DAP) ................... 97 CHAPTER 3 Response of green foxtail to fluazifop-butyl at 18, 24, and 30 C ..................... 112 Response of Japanese millet to fluazifop-butyl at 18, 24, and 30 C .................... 114 ix Figure Response of four- (A) and six-leaf (B) Japanese millet, and four- (C) and six-leaf (0) green foxtail to fluazifop-butyl, with morning (8:00 a.m.), mid-day (3:00 p.m.) and evening (10:00 p.m.) applications ........................ 119 Effect of simulated rainfall on the response of Japanese millet (A) and green foxtail (B) to fluazifop-butyl ...................... 123 CHAPTER 4 Response of large crabgrass (A) and stinkgrass (B) to fluazifop-butyl at three carrier volumes, 1982 ....... 137 Response of large crabgrass (A) and stinkgrass (B) to fluazifop-butyl at four carrier volumes, 1983 ...... 139 Response of large crabgrass to fluazifop-butyl at four adjuvant concentrations (% v/v) ............ 142 INTRODUCTION The development of selective pre- and postemergence herbicides, typified by the introduction of 2,4-D in the early 1940's, has greatly influenced modern crop production practices. Many current production systems are designed around weed control practices and available herbicides. Many of these chemicals provide long-term control of annual broadleaf and grass weeds. However, the increased adoption in recent years of conservation tillage for reducing production costs and minimizing soil erosion, along with a need for short-term residual chemicals.which.allow unrestricted crop rotation, has increased the demand for selective postemergence herbicides. Many soil applied herbicides do not control perennial grasses such as johnsongrass (Sorghum halepense (L.) Pers.) in the South and quackgrass (Agrogyron M (L.) Beauv.) in the North. Therefore, effective and selective postemergence grass herbicides are needed. The potential use of postemergence grass herbicides (graminicides) in horticultural cropping systems is extremely large. Herbicide development on high acreage crops such as corn (Zgg_mgy§_Ln), soybeans (Glycine max L.), wheat (Triticum aestivum L.), and cotton (Gossxpium hirsutum) has preempted efforts on limited acreage vegetables and fruits. As a result, the availability of registered compounds for use in horticultural crops is relatively less and often inadequate. Annual grasses such as large crabgrass (Digitaria sanguinalis (L.) Scop.) and barnyardgrass (Echinochloa crus-galli U”) Beaqu as well as perennial grasses such as quackgrass, are serious weed problems in horticultural crops. Selective control of both annual and perennial grasses, good broadleaf crop tolerance, and considerable flexibility in the time of application, are attributes which make postemergence graminicides desirable. This study had three objectives: first, to investigate the responseeof selected annual weedy grasses and grain crops to foliar applications of fluazifop-butyl, and to determine optimal usage rates; second, to examine the influence of environmental factors such as temperature, diurnal variation, and rainfall on the activity of fluazifop-butyl; and third, to determine the effect of spray application factors such as carrier volume and adjuvant concentration, on fluazifop-butyl activity. CHAPTER 1 REVIEW OF LITERATURE The development of postemergence grass herbicides (graminicides) within the past decade has offered a new strategy for crop management. Before the discovery of graminicides, control of grasses in broadleaf crops was accomplished primarily with preemergence or pre-plant incorporated herbicides, or by mechanical methods. Most of those chemicals required extensive land preparation before or at application and often were not effective in minimum or no—tillage cropping systems. The discovery of selective grass herbicides has provided an opportunity for expanded use of conservation tillage. In addition, crop producers can delay herbicide applications to determine weed pressures and damage thresholds before making management decisions, an idea compatible with the philosophy of Integrated Pest Management. Optimum usage of the new graminicides will require a thorough understanding of their properties and the influence of various external factors affecting their activity. Overview gf_Postemergence Graminicides. A general description of the nomenclature, history, herbicidal activity, and physical properties for diclofop-methyl (3, 129), metriflufen (22), difenopenten (39), sethoxydim (lCL 132), R0-l3-8895 (106), CGA-82725 (43, 159), DPX-Y6202 (68, 157), fluazifop-butyl (lll), haloxyfop-methyl (64, 180, 190), mefluidide (137), PPOO5 (112), and RE- 36290 (40) are presented in Table: 1 and 2. Chemical names and molecular structures of these herbicides are shown in Figure 1. The first graminicides were phenoxy-phenoxy (diphenyl ether) derivatives. This includes diclofop-methyl, metriflufen, difenopenten and R0-l3-8895. Some of the more recent chemicals are 2-pyridinyl oxy- phenoxy propanoic acid derivatives, including CGA-82725, fluazifop- butyl, PP005, and haloxyfop-methyl. The remaining herbicides include mefluidide, an acetanilide derivative, sethoxydim, a cyclohexane dione derivative, and DPX-Y6202, a 2-quinoxalinyl oxy-phenoxy propionic acid, ethyl eshn~derivative. This literature review will concentrate on those herbicides currently under development or production. Very little information is available for cloproxydim (RE-36290, so it is not included in the following discussion. Information pertinent to some of the discontinued graminicides will be discussed when it relates to physiological cu“ environmental factors which could affect the performance of the other herbicides. Tolerant Species and Potential Uses. A wide number of broadleaf weeds, sedges, non-grass agronomic crops, and horticultural crops have shown tolerance to all of the graminicides (18, 34, 65, 69,182, 115, 118, 123, 132, 138, 155, 159, 162, 171, 172, 180), even at rates two to four times the amount necessary to control grasses. Excellent tolerance has also been demonstrated in selected monocotylendonous crops such as onions and asparagus (34, 132). In some instances, chlorosis.and necrosis have been noted on broadleaf plants treated with graminicides, but crop 5 Table 1. General characteristics of selected postemergence graminicides.a Experimental Common Trade Product Year Grasses Designation Name Name Manufacturer Introduced Controlled HOE-23408 Diclofop- Hoelon- Hoechst, A.G. 1973 Annual methyl USA Frankfurt, only Germany Hoe—grass- Canada HOE-29152 Metriflufen Hoechst, A.G. 1976 Annual Frankfurt, (discontinued Perennial Germany in 1978) KK-BO Difenopenten Chevron Chem. 1978 Annual Co., Richmond, (discontinued Perennial CA in 1981) BAS-9052 Sethoxydim Poast BASF-Wyandotte 1978 Annual Corp., Passippany Perennial N.J. R0-13-8895 HLR Sciences Inc. 1980 Annual Vero Beach, FL (discontinued Perennial in 1982) CGA-82725 Ciba-Geigy 1980 Annual Ltd. Basle, (discontinued Seedling Switzerland in l984) DPX-Y6202 Assureb E.I. duPont de 1980 Annual Nemours & Co., Perennial Inc., Wilmington, DE PP009 (USA) Fluazifop- Fusilade Imperial Chemical 1980 Annual TFll69 (Canada) butyl Industries, Ltd. Perennial London, England Dowco 453 Haloxyfop- Verdictb Dow Chemical Co. 1981 Annual methyl Midland, MI Perennial MBR-12325 Mefluidide Embark 3M Company Annual Vistar Minneapolis, MN Perennial Ppoosc Fluazifop-d 1c1 Americas Inc. 1984 Annual p-butyl Goldsboro, NC Perennial RE—36290 Cloproxydimd Selectone Chevron Chem. Co. Annual Richmond, CA aInformation not included in the table was unavailable. bProposed trade name. c(R) enantiomer of fluazifop-butyl. dProposed common name . Table 2. Physical properties of selected postemergence grass herbicides.a Herbicide Physical Melting Boiling Vapor Solubility State Point Point Pressure in H20 Diclofop-methyl colorless 39-41C 174-176C (20c )- 50 ppm odorless 3 x lO-7mm Hg solid Metriflufen (43(:)— 1.4 ppm 9.7 x io-Storr Difenopenten viscous (20C )- (25 c ) < 1 ppm liquid 3.33 x 10-9mm Hg Sethoxydim amber, (25C )— (25(:)-48 ppm odorless 1.6 x 10-7mm Hg oily, liquid R0-13-8895 colorless very slightly odorless soluble CGA-82725 (20 C )-3 ppm DPX-Y6202 white 91 c (20c )- (20 c)—o.3 ppm crystalline 3 x 10-7mm Hg solid . Fluazifop-butyl amber, 5 C (0.5 mm Hg) (20(:)- 2 ppm odorless 167 C 5.5 x 10'5Pa. liquid Haloxyfop-methyl light (25(3)- 1.5 ppm amber 3.87 x 10-7mm Hg _ liquid Mefluidide white 183-185 C 180 ppm crystalline solid PP005b light none at 4.1 x 10-7mm Hg 2 ppm amber, atm. pressure odorless liquid RE-36290 pale yellow (20(3)- almost viscous oil 1 x 10-7mm Hg insoluble aInformation not included in the table was unavailable. ”1 R) enantiomer of fluazifop-butyl. Figure 1. Common name (if available), chemical name, and molecular structure of selected postemergence grass herbicides. Diclofop-methyl (HOE-23408) 13 (HQ 0 @— O—CH — coocH3 c1 (methyl 2—[4—(2,4-dichlorophenoxy)phenonypropanoate) Metriflufen (HOE-29152) (methyl 2- [L( (4' -trifluoromethyl phenoxy) phenonypropanoate) Difenopenten (KK-BO) w—Q QC” O—CHCH 3:cncoocnzcn3 (ethyl 4- [4-( L [trifluoromethyl]phenoxy) phenoxy- -2- pentenoate) Sethoxydim (BAS-9052) 0 CH2- CH2. CH3 H C CH _. ‘_’ __ __ 3| 3 C—N 0 CH2 CH3 H2O CH \ /\ 5 CH2 0H (2-[1-(ethoxyimino)buty1]-5-[2-(ethylthio)propyl]-3—hydroxy-2- cyclohen —1-one) R0-l3-8895 13 13 F3C o o— cn—c—o—Nzc 11 1 0 CH3 (acetone 0-[D-(2-[p-(a, a, a-trifluoro-p-toyl)onyphenoxy) propionyl]oxime) CGA-82725 40 (2 propynyl 2- [4- ([3, 5- -dichloro- 2- pyridinyl]oxy)phenoxy] propanoate) 10 DPX-Y6202 c1 N (CH3 I / . Q ............ N (2-[4—[(6-ch1oro-2-quinoxalinyl)ony-phenony-propionic acid, ethyl ester) Fluazifop-butyl (PP 009) CH3 / \ ' 13C 0 O 0— cu- fi- o—cnzcnzcnzcn3 N o ((tU-butyl 2-[4-([5-(trif1uoromethyl)-2-pyridinyl]oxy)phenoxy] propanoate) Haloxyfop-methyl (DOWCO 453) c1 F3C @ o—.— 0—CH — coocn3 _... N 1 C113 (methyl 2-[4-([3—chloro-5-(trif1uoromethyl)—2-pyridinyl]oxy) phenoxy]propanoate) 11 Mefluidide (MBR-12325) CH3 NHSOZCF3 0 CH3 NHCOCH3 (N-[2,4-dimethy1-5-([(trif1uoromethy1)suifony]]amino)pheny1] acetamide) RE-36290 (Proposed common name is Cioproxydim) O is -S-CHCH c=N-O- CH CH: CHC] 2 ' 2 CHZCHZCH3 0H CH3CH2 ((E,E)-2-1[(1-[(3-ch1oro-Z-prOpeny1)oxy]imino)buty1]-5-[2- (ethythio)propy1]-3-hydroxy-2-cyc1ohexen-1-one) PPOOS (Proposed common name is f1uazifop-p-buty1; moiecuiar structure is R enantiomer of fiuaziiop-butyi) (butyi(R)-2[4-([5-(trif1uoromethy1)-2-pyridiny1]oxy)phenoxy] propanoate) 12 yields were not significantly affected (l9, 35, 82, l08, l23, l40, l55, l7l). Morrow and Murphy (l40) observed a severe yellowing of the leaf margins near the petioles of white potatoes (Solanum tuberosum L. 'Kennebecfl treated with DPX-Y6202, but no subsequent yield reductions. Parker (l55) noted phytoxicity in some mint (flefltha spJ trials and thought it could be related to the crop oil concentrate used with the graminicide. Chairez et al. (35) compared a number of graminicides at various rates on soybeans (Glycine max. L.), and discovered that only mefluidide at rates above 0.28 kg/ha significantly reduced initial soybean fresh and dry weights, in greenhouse trials. Through time, plants recovered from injury. In field trials, soybean yields did not differ among herbicide treatments (35). With ornamentals, Bing and Macksel (19) found that fluazifop-butyl, from now on referred to as fluazifop seriously burned the foliage of two cultivars of container grown azaleas (Rhododendron obtuswn(Linle Planch),'Hinodegeri'and 'Hinocrimsonk These plants later recovered. Kuhns et al. (123) also reported that fluazifop injured the foliage of certain azalea varieties, however sethoxydim did not. Annual Grass Susceptibility. One of the most advantageous characteristics of the selective grass herbicides is the wide range of grasses controlled. However, the chemical rate necessary to sufficiently control annual and perennial grasses is a function of both the herbicide used and the species to be control led (Table 3). From Table 3, it could be stated that the general order of herbicides from most to least effective on annual grasses is: haloxyfop-methyl > '13 Table 3. Chemical rates necessary for adefluate control (> 80%) of various annual and perennial grasses. Only selecte graminicides currently labelled or under later stages of development are included. At the time of application, grasses are assumed to be actively growing and not under environmental stresses.a diclofop- .fluazifop haloxyfop- Selected ”91“!) sethoxydim DPX-Y6202 butyld methyl Grass Rateb Growthc Rate Growth Rate Growth Rate Growth Rate Growth Species stage stage stage stage stage annual rye rass mi barnyard- rass A) 0.84-1.12 8 0.11 2-4 0.28 NC 9 0.09 2-4 0.07 2-4 bermuda- rass P) 1.12 8 0.28 8 0.28 B 0.28 8 0.14 8 corn (A) 0.84-1.12 11 0.12-0.22 11 0.28 14 0.06 11 0.06 11 fall panicum (A) 1.12 8 0.22 1-5 "NA 0.28 2-5 0.14-0.28 2 giant foxtail (A) 1.12 2 0.12 9 0.04 1 0.06-0.12 9 0.07 2 goose- o grass (A) 0.84-1.12 8 0.15 8 NA 0.15 8 0.14-0.28 2 green foxtail (A)f 0.84-1.12 3 0.11 2-4 NA 0.23 NC 2-4 0.07-0.09 2-4 Johnson- rass (P) 1.12-1.4 8 0.28 6 0.28 10 0.28-0.56 6 0.1-0.4 6 large crab- grass (A) 1.12-1.4 7 0.22 1-5 0.28 8 0.28 2-4 0.07-0.14 2-4 cats (A) 1.12 13 0.045 11 0.28 13 0.07 11 0.14. 13 quack- grass (P) NC 1.1 11 0.5 11 1.0 11 0.5 11 rye (A) 1.12 NC 13 0.28 13 0.28 13 0.28 13 0.14 13 shatter- cane (A) 1.12-1.4 8 0.11 2-4 NA 0.09 2-4 0.07 2 sorghum (A) 1.12 NC 10 0.1 1 0.28 10 0.1 1 0.03 wheat (A) NC 0.045 11 0.28 13 0.07 11 0.14 13 wild oat (A) 1.12 8 0.28 13 0.28 13 0.28 13 0.14 13 wild - proso- millet (A) NC 0.11-0;20 10 NA 0.14-0.28 10-11 0.14 10 witch- grass (A) 1.12 8 0.28 8 0.28 8 .28 8 0.14 . 8 yellow foxtail (A) 1.12-1.4 8 0.12-0.22 1-5 0.28 10 0.14-0.28 9-12 0.09 2-4 aThis table was compiled from the following references: 3, 5, 7, 15, 17, 20, 25, 26, 27, 37, 41, 45, 52, 64, 66, 67, 69, 71, 85, 90, 97, 111, 117, 136, 143, 162, 164, 167, 168, 176, 177, 182, 202, 204, 206. bkg active ingredient per ha. c0:0.1 in, 1-1-2 in, 2-2-3 in, 3:3-4 in, 4:4-5 1n, 5:5-6 in, ass-12 in, 7-0-1 1f, 8=l-2 1f, 9:2-3 1f, 10:3-4 1f, 1124-5 1f, 12:5-6 1f, 13=tillering, 14:1 tiller, 15:30 days after planting, NA=information not available, NC=not controlled. dInitial research indicates PP005, the (R) enantiomer of fluazifop-butyl, will require rates one-half of fluazifop-butyl for control of sensitive grasses. e(A) = annual, (P) - perennial. ‘ fGiant green foxtail (Setaria viridis var. major (Gaud.) P050.) and robust purple foxtail (var. robusta-purpurea Schreiber) are generally more tolerant than green foxtail to the graminicides. 1.12 8 0.28 15 NA 0.28 NC 15 0.14 15 14 fluazifop 3 DPX-Y6202 = sethoxydim > diclofop-methyl. Many researchers have found that annual grasses are more effectively controlled at smaller stages of growth (4, 7, 27, 38, 65, 76, 94, 105, 117, 139, 141, 148, 162, 167, 182, 196, 198, 208). This is probably'most important with diclofop-methyl, hereafter referred to as diclofop. Chernicky et a1. (38) reported a significant reduction in the control of large crabgrass (Digitaria sangginalis (LJ ScopJ, goosegrass (Eleusine indiga U") Gaerth, and broadleaf signalgrass (Brachiaria platyphylla (Griseb.) Nash) as grasses advanced from 12 to 21 cm, to 32 to 48 cm. This result was consistent with both sethoxydim and R0-l3-8895. The reduced activity at later stages of growth was stated to be of little importance, since season-long grass competition with soybeans (cv. 'Braggfl would be expected to suppress yields, making early season control more practical. In addition to their use in agronomic and horticultural food crops, the graminicides will be widely used in perennial broadleaf forages, nursery ornamentals, and other non-food crops. One interesting potential application of the graminicides is for selective grass control in turf (44, 55, 103, 209, 212). Cisar and Jagschitz (44) compared CGA-82725, haloxyfop-methyl, fluazifop, sethoxydim, and 0PX-Y6202 for smooth crabgrass (Digitaria ischaemum (Schreb.) Muhl.) control in red fescue (Festuca rubra L. 'Jamestown') and perennial ryegrass (L01 ium perenne L.) + fescue turf. They found that two-week split applications of 0.075 lb active ingredient per acre (ai/A) of CGA-82725 and haloxyfop-methyl (hereafter referred to as haloxyfop), provided 94 and 98% control of smooth crabgrass, respectively. Injury 15 to each turfgrass was minimal. Split applications of sethoxydim at 0.125 lb ai/A yielded 97 to 99% control of smooth crabgrass. Red fescue sustained acceptable levels of injury, but perennial ryegrass was severely'thinned. Poor control of smooth crabgrass, but acceptable levels of turf injury, were noted with fluazifop and DPX-Y6202 at rates as high as 0.075 lb ai/A. The graminicides can also be used to suppress cereal crops, which are usedcn1high organiCInatter soils to minimize soil erosion (153, 191). Palmer (153) found that planting barley (Hordeum vulgare L,) as a cover crop between rows of sugarbeet (Beta vulgaris L”) reduced soil erosion and wind-blown loss of the fine beet seed. Fluazifop effectively killed the barley before it became too competitive with the established sugarbeet. Application of the grass herbicides are primarily postemergence, but Dale (50) proposes treating crop seeds with the herbicide. In greenhouse studies, soybean seeds coated with a mixture of tung oil and fluazifop adequately controlled goosegrass. No phytotoxicity to the soybeans was observed. Mutch and Meggitt (141) analyzed the affect of season-long giant foxtail, ‘fall panicum (Panicum dichotomiflorum Michx.) and barnyardgrass (Echinochloa crus:galli (LJ Beauv§)competition with soybeans. Grass densities of 56 plants/m2 reduced soybean yields 38%. When grasses at this density were removed by sethoxydim six weeks after emergence, soybean yield was reduced by 15% (141). Generally, the increasing competitive abilitorof annual grasses throughout the growing season and the higher herbicide rates necessary to control them, make early season control more efficient and economical. 16 Perennial Grass Susceptibility. Compared to annuals, perennial grasses require higher rates of the graminicides to be controlled. This is primarily due to their vegetative reproduction. Evidently, the grass herbicides must translocate throughout the foliage as well as any underground vegetative structures to insure long-term control. Perennial grasses are also affected differently by various herbicides (Table 3). The general order of herbicide effectiveness from most to least is: haloxyfop > DPX-Y6202 > fluazifop = sethoxydim >> diclofop. Diclofop is effective on some seedling perennial grasses but not established perennials. This could partially result from its limited mobility (129). A number of studies have investigated the use of split or sequential applications of graminicides. For both johnsongrass (Sorghum halepense (L.) Pers.) and quackgrass (Agropyron repens (L.) Beauvu) at least equal and often superior grass control can be obtained by splitting applications (10, 46, 64, 67,101, 111,120, 131,162, 192, 195, 199, 200). Under greenhouse conditions, Hicks and Jordan (101) found that a minimum of 24 h between split applications of sethoxydim, fluazifop, and haloxyfop was necessary to obtain greater bermudagrass (Cynodon dactylon (L.) PersJ, *wirestem muhly (Muhlenbergia frondosa (Poir.) Fern.), and quackgrass control, than with a single application. The recommended interval between split applications for fluazifop (111) and sethoxydim (10) is one to three weeks. Split applications can be especially advantageous under conditions such as low relative humidity and high temperature, low soil moisture, heavy infestations of grass, or applications early in the growing season when only a fraction of the grass has emerged (64, 17 111, 162%. Plowman etial.(162) reported more effective long-term control of johnsongrass with eight-day sequential applications of fluazifop at 0.28 kg/ha than with a single application of 0.56 or even 0.84 kg/ha. Johnsongrass at the time of the first application was in the two-leaf stage. They suggested that johnsongrass may not translocate fluazifop very well to the rhizomes at an early stage of growth, and splitting applications could provide season-long control. Cultivation in addition to a single application or as a substitute for the second treatment of a split application, has also been effective (10, 46, 111, 131, 162, 192, 200, 205, 206). Colby et al. (46) obtained effective control of johnsongrass, bermudagrass, and quackgrass at fluazifop rates of 0.28 to 0.56 kg/ha, but only if rhizomes or stolons had previously been thoroughly fragmented by tillage. Higher rates were required to control undisturbed grasses. Cultivation of quackgrass as soon as one day after treatment with sethoxydim or difenopenten provided more effective season-long control than treated quackgrass without cultivation (206) Perennial grasses are generally more effectively control led at one growth stage than another. DPX-Y6202 (67), sethoxydim (10), fluazifop (111), or haloxyfop (64), are most effective on bermudagrass up to four inches in height or with stolon length up to six inches. Johnsongrass is most susceptible to sethoxydim at 6 to 18 inches in height (10, 90), 6 to 12 inches for fluazifop (90, 111), less than 24 inches for DPX- Y6202 (68), and 15 to 18 inches for haloxyfop (64). Applications to johnsongrass shorter than six inches generally results in sufficient initial control but significant rhizome regrowth. Quackgrass control 18 by DPX-Y6202 (68), sethoxydim (10, 52, 206), fluazifop (52, 92, 111, 120, 204, 205), and haloxyfop (52, 64) was generally most effective at the three to five-leaf stage. Harker and Dekker (92) evaluated the translocation of 14C-sucrose, -sethoxydim, -f1uazifop, and -haloxyfop in three-, five-, and seven-leaf quackgrass plants. They reported that the most translocation took place in five-leaf quackgrass, which suggests this is the optimum stage for control. Research by Dekker (52) indicates that field application of fluazifop, haloxyfop, sethoxydim, and DPX-Y6202 to five-leaf quackgrass provides greater initial and long-term control than treatments at the three-leaf stage. However, Kells (120) reports greater distribution of 14C-fluazifop in two- to three-leaf than five- to six-leaf quackgrass. Also, greenhouse results revealed quackgrass control was significantly greater on two- to three-leaf than five- to six-leaf quackgrass. Variations between field and greenhouse conditions as well as laboratory techniques could explain these discrepancies. Regardless of the growth stage when the graminicides are applied, perennial grasses often overcome the effects of herbicides (l, 17, 52, 54, 90, 125, 162, 206, 218). Naldecker and Nyse (206) found that quackgrass control in soybeans with sethoxydim, difenopenten, and R0- 13-8895 at 1.1 kg/ha was 91, 88, and 98%, respectively, 32 days after treatment.(DAT), After 105 days, control had dropped to 79, 75, and 85%, respectively; Soybean yield 120 DAT was significantly higher for each plot treated at 1.1 kg/ha. Quackgrass control at this rate, 470 DAT, had declined for sethoxydim, difenopenten and R0-l3-8895 to 61, 41, and 55%, respectively. Soybean yields 485 DAT were not 19 significantly different from untreated plots. They concluded that satisfactory quackgrass control with minimal affects on soybean yields, was only possible for one growing season. Dekker (54) conducted a three year study of quackgrass control with various graminicides, each applied once at 1.0 kg/ha. He concluded that only haloxyfop provided control for more than one year. The other graminicides, including fluazifop, sethoxydim, R0-13-8895, and DPX-Y6202 could only be utilized to provide control for one year. Although many annual and perennial grasses are sensitive to the postemergence grass herbicides, there are a number of turf and forage grasses which have shown degrees of tolerance (25, 26, 41, 79, 129). In general, annual bluegrass (Egg annua LJ, annual fescues, and fine- leaved perennial fescues demonstrate the most tolerance (25, 26). However, haloxyfop (26, 64, 79), and DPX-Y6202 (26, 68) have shown some potential for controlling annual bluegrass. Environmental Factors Influencing Efficacy. Many reports indicate that environmental factors such as temperature, relative humidity, soil moisture, timing of application, and rainfall, reduce or enhance the effect of the graminicides. Some of the specific effects of air temperature, relative humidity, and soil moisture, on herbicide uptake and translocation will be discussed later. Nalewaja et al. (142) stated that diclofop was more effective at 10 C than at 30 C for wild oat (Avena fatua L.) control, however, for yellow foxtail (Setaria lutescens (Weigel) Hubb.L, 30 C air temperatures at application provided greater control than 20 C. Chow 20 (41) also reported greater diclofop activity on wild oats at reduced temperatures. Shoot dry weight at 1.1 kg/ha of diclofop decreased from 20.4 to 10.1, and 3.9% below the control at 12, 20, and 28 C, respectively. Root dry weight reductions fol lowed a similar trend. Chow concluded that diclofop at 1.1 kg/ha was most effective for wild oat control early in the spring, when air temperatures are lower. In contrast, Kells et al. (122) noted phytotoxicity of fluazifop was more pronounced on quackgrass treated at 30 C than 20 C, when chemical rates were 0.28 kg/ha. Increasing the herbicide rate to 0.56 kg/ha overcame the phytotoxicity response to temperature (122). Rhodes and Coble (170) studied the affect of sethoxydim on goosegrass under different day/night temperature regimes. The results indicated goosegrass control increased as day/night temperatures increased. A temperature regime of 16/4 C prevented effective goosegrass control with up t01$22 kg/ha of herbicide. Hartzler and Foy'(96), however, did not find a difference in large crabgrass control with sethoxydim or CGA-82725 at temperatures of 16, 24, or 32 C. Toxicity of the graminicides has also been influenced by the relative humidity UH” during and after grass treatment (48, 134, 213). Bermudagrass was generally more susceptible to sethoxydim and difenopenten when treated under high (100%) than low (40%) humidity conditions (213). Mcwhorter (134) reported significantly greater johnsongrass control with metriflufen at 100 than 40% RH, at both 24 and 32 C. A¢.24 C, the presence of surfactant enhanced metriflufen activity on johnsongrass at 40% RH but not at 100% RH. Many researchers have documented the importance of adequate soil moisture for control of annual and perennial grasses (2,5L 38, 62, 21 122, 142, 166, 169, 208). Akey and Morrison (2) found that lowering the gravimetric soil moisture content from 20 to 10%, resulted in 90 and 55% reductions in wild oat growth, respectively. Duration of moisture stress after spraying diclofop on wild oat also was significant. Maintaining a soil moisture content of 10% for two and ten days before removing the water stress, resulted in an 81 and 68.3% weight reduction in wild oat, respectively. They also found the moisture content of wild oat during herbicide application directly' affected control. Plants under water stress when treated, fol lowed immediately by water application to bring the moisture status equivalent to unstressed plants, were more tolerant to diclofop than treated plants maintained under normal conditions. These results were similar to those found earlier by Dortenzio and Norris (62). Although low soil moisture impaired diclofop activity, Dortenzio and Norris (62) discovered that increasing the rates of herbicide minimized this effect. In some situations, the time of day during which a postemergence herbicide is applied has been reported to affect grass control (6, 73, 146). Ashley (6) reported significantly greater large crabgrass control in snap beans (Phaseolus vulgaris L.) when diclofop applications were made in the early morning or evening, as compared to those made at mid-day. Working with itchgrass (Rottboellia exaltata LJfi) under various soil moisture conditions, Nester and Harger (146) noted diclofop applications provided the most consistent control when made in the morning. ‘This was especially'true when droughty conditions existed. They suggested moisture stress was most severe on itchgrass during the middle of the day, making herbicide applications less 22 reliable than if plants were treated early in the day. Interest on the affect of rainfall after application has led to several studies on herbicide retention and subsequent effectiveness. Studies with simulated rainfall have indicated herbicide efficacy is significant after only/(L25 to 2 h of plant eXposure to sethoxydim (48, 91,170, 213), 4 to 12 h of diclofop (142, 152), l to 8 h of fluazifop (124, 162), 1 to 3 h of DPX-Y6202 (68, 156), less than 1 h of CGA-82725 (124), and 2 h of haloxyfop (64, 124). Laube and Arnold (124) compared CGA-82725, fluazifop, and haloxyfop efficacy on yellow foxtail and volunteer corn (ZEEHEEXE.LQL Simulated rainfall was applied at a rate of 1.7 cm various times after herbicide application. Adequate control of yellow foxtail was attained when rainfall was delayed 8 h, 2 h, and immediately after application of fluazifop, haloxyfop, and CGA-82725, respectively. Volunteer corn control was satisfactory when rainfall was delayedZZh for fluazifop and immediately after application of haloxyfop and CGA-82725. The relatively short time period required between herbicide application and rainfall suggests great flexibility in making applications under adverse conditions. Application Factors Affecting Efficacy Spray Volume. Many studies have evaluated the carrier volume effect on graminicide activity (7, 29, 37, 49, 93, 116, 121, 158, 181, 187, 207). Kells et al. (121) reported quackgrass control with sethoxydim decreased from an average of 61% at a spray volume of 35 L/ha, to 27% at a spray volume of 262 L/ha. Simkins and 0011 (187) also reported greater quackgrass control at lower carrier volumes, but 23 only when herbicide applications were made to grasses at the two- three-leaf stage. Quackgrass treated at the four- to six-leaf stage was controlled more effectively at a spray volume of 300 L/ha than 20 L/ha (187). Volunteer corn control with sethoxydim at 0.1 lb/A decreased from 86 to 60 to 47% at carrier volumes of 5, 10, and 20 gallons per acre (GPA), respectively (37). However, Charvat and Kinsella (37) discovered that differences between spray volumes disappeared as sethoxydim rates were increased. Other researchers have also noted, that spray volume differences are most pronounced at marginal control rates of grass herbicides, and are masked at higher rates (29, 49, 93, 158). The interest in lowering spray volumes for improving grass control has been helped by the development of control led droplet applicators (CDAs). Pearson and Bode (158) state that previous attempts to employ the use of low-volume applications were impaired by frequent clogging of the small orifice nozzle tips required in these spray systems. Also, low volume application systems are more likely to generate small spray droplets, which could create drift problems. CDAs are designed to circumvent these problems. Samir and Russ (181), as well as Anderson (5), have reported improved grass control as the spray volume was increased. Diclofop activity on volunteer corn at(L84 kg/ha, was enhanced when carrier volumes were doubled from 187 L/ha to 374 L/ha (181). Although increases or decreases in spray volume can improve grass control, some researchers have found spray volume not to be a significant factor (8, 33, 77, 85, 89, 95, 113, 188, 195). One possible explanation is that the herbicide rates used in some of these studies were too high, and masked any volume differences. 24 Adjuvants. Adjuvants in spray solutions containing graminicides are important in affecting uniform herbicide distribution and retention on target species, and perhaps may influence herbicide penetration. Studies with diclofop (41, 142, 151, 182), metriflufen (134), sethoxydim (5, ll, 29, 36, 38, 47, 75, 91, 96, 126, 131, 143, 145, 199), R0-13-8895 (38, 91, 96), fluazifop (4, 5, ll, 29, 75, 80, 127, 143, 145, 202), CGA-82725 (5, 75, 143, 145), haloxyfop (11, 29, 143, 145), and DPX-Y6202 (11) have shown significantly greater weed control when various adjuvants were present in the spray solution. Anderson (5) found that annual grass control was not enhanced by increasing the concentration of crop oil concentrate from 0.5 to 2% v/v in solutions containing 0.1 lb/A of haloxyfop, fluazifop, sethoxydim, or CGA-82725. Kells et al. (121) reported similar results. However, Buhler and Burnside (29) reported that as the concentration of crop oil concentrate increased from 0.1 to 5% v/v, forage sorghum (Sorghum bicolor (L.) Moench 'Rox Drange') control improved significantly. This was true in solutions containing fluazifop, haloxyfop, or sethoxydim. Buhler and Burnside (29) noted however, that as the herbicide rate increased, differences in forage sorghum control with increasing adjuvant concentrations, diminished. Other researchers have reported reductions in adjuvant activity as the graminicide rate increased (38, 41, 47, 75, 93, 96, 126). Cranmer and Nalewaja (47) compared sethoxydim rates of 0.1 and CLZ kg/ha at various concentrations of a crop oil, AtPlus 411F} They found that the concentration of AtPlus 41 1F needed for effective yellow foxtail control decreased as the rate of sethoxydim increased. However, adequate foxtail control required 25 higher concentrations of crop oil for plants at the six-leaf stage than the four-leaf stage. There are a wide number of adjuvants which can be used to enhance the activity'of the grass herbicides. 'These range from the nonionic surfactants such as X-77, to petroleum oil concentrates, and crop oil concentrates e4; soybean oil plus surfactant. In general, use of crop oils and petroleum oil concentrates have given better results than nonionic surfactants. However, Veloviixfl1(202) found that foxtail millet (Setaria italica (L.) Beauv.), treated with fluazifop at 0.04 to (L07 kg/ha, was injured sooner and controlled better with 0.1% v/v X-77 than 1% v/v of crop oil concentrate. At fluazifop rates above 0.14 kg/ha, these differences diminished (202). Comparisons between petroleum oil additives and crop oils have generally resulted in small to non-significant differences (ll, 31, 36, 93, 126, 145, 207). Performance of the postemergence grass herbicides under adverse conditions can be significantly affected by adjuvants. Porter and Harvey (163) observed that crop oil concentrate finproved fluazifop activity on wild proso millet (Panicum milliaceum L.) under dry climatic conditions. Adjuvants can improve herbicide performance by reducing the surface tension of the grass leaf, allowing more uniform coverage of the target plant (79) This can be especially advantageous when grass weed populations are dense. Adjuvants can also enhance herbicide penetration into leaves (79), which can aid control of mature grasses. McWhorter and Wills (133) reported 14C-mef1uidide absorption and translocation in johnsongrass was significantly increased by the use of nonoxynol (u(p-Nonylphenyl)- hydroxypoly'(oxyethylene)) and 26 ethomeen (oleyl tertiary amino ethylene oxide condensate). This was especially true under conditions of low relative humidity'(40 vs. 100%) and high temperatures (32 vs. 22 C). Herbicide Interactions. Within the past 10 to 15 years, herbicide development has increasingly moved toward selective, postemergence broadleaf and grass control. The need for broad-spectrum weed control and limiting application costs, has sparked considerable interest in tank-mixing various postemergence herbicides. Unfortunately, there are varying degrees of antagonism from the addition of graminicides to broadleaf herbicides (Table 4 and 5). Often, the antagonism is thought to be a result of physiological processes in target plants, and not physical incompatibilities (Hi the herbicides (79). Generally, antagonism is noted as aidecline in grass control, but some studies have also demonstrated a reduction in broadleaf weed control (12, 175, 194). Ritter and Harris (175), with a tank-mix of acifluorfen and R0- 13-8895, noted that increasing the rate of RO-13-8895 while maintaining the acifluorfen rate, resulted in a decreasing level of morningglory (Ipomoea sp.) control. Tank-mixing with broadleaf herbicides has also demonstrated compatibility (9, 32, 42, 58, 60, 88, 98, 99, 104, 119, 151, 194, 202, 203). For example, Himmelstein and Peters (104) reported that tank- mixing sethoxydim, fluazifop, or haloxyfop with 2,4-DB, provided adequate broadspectrum weed control in seedling alfalfa (Medicago sativa LJ. In some instances, significant crop injury has resulted from applying two postemergence herbicides together (16, 32, 51, 57, 59, 98, 99, 100, 102, 104, 119, 202). In established alfalfa, 2,4-DB tank- 27' .pxuan-nomw~mapm mo gonorucmcu.amvu .mmvvu'acw; wmmpcooen to was: pauNEmsu so» m opnah momu .mmocmcweoc negro mum mwmwzucocoa =_ memnE=z .—ogucou vow; wompcoogn Lo\ccm mmwgm c? copuusumc a ma Emwcomouc-XNQ arexxo;pam _N;Naeumocaxo~ae umooaa mNNNN- we moxweixcmu soc» Emwcoomucm kucogmm .v m—aoh 28 Table 5. Common name and chemical name of various broadleaf herbicides. Common Name Chemical Name Acifluorfen Bentazon Bromoxynil Chloroxuron 2,4-0 2,4-DB Desmedipham Dicamba Dinoseb Endothall Linuron MCPA Phenmedipham PPS-844a 5-[2-ch1oro-4-(trifluoromethyl)phenony-Z- nitrobenzoic acid 3-isopropyl—l H-2,l,3-benzothiadiazin-4 (3 H)- one 2,2-dioxide 3,5-dibromo—4-hydroxybenzonitri1e 3-[p-(p-chlor0phenoxy)phenyl]-l,1-dimethylurea (2,4-dichlorophenoxy) acetic acid 4-(2,4-dichlorophenoxy) butyric acid ethyl m-hydroxycarbanilate carbanilate (ester) 3,6-dichloro-o-anisic acid 2-sec-butyl-4,6-dinitrophenol 7-0xabicyc10[2,2,l]heptane-2,3-dicarboxylic acid 3-(3,4-dichlorophenyl)-l-methoxy-1-methylurea [(4-chloro-o-toyl)oxy] acetic acid methyl m-hydroxycarbanilate m-methylcarbanilate aChemical name not yet released. 29 mixed with sethoxydim or fluazifop plus crop oil concentrate, produced leaf necrosis, epinasty and stunting (57). Dewey (57) noted the stunting persisted beyond the second cutting. He suggested that the crop injury was the result of increased foliar uptake of 2,4-DB, promoted by the oil concentrate or other adjuvants contained in the formulation of the graminicide. Dexter (58) found that addition of an oil concentrate to mixtures of desmedipham and sethoxydim, diclofop, R0—l3-8895, CGA-82725, or fluazifop, improved control of wild oats compared to treatments without an oil concentrate. The penetration of I4C-haloxyfop into German millet (Setaria italica (LJ Beaqu was significantly reduced when tank—mixed with bentazon (210). However, Todd and Stobbe (197) indicated that the antagonism between diclofop and 2,4-0 could not be explained by decreased penetration of diclofop into wild oat. They reported that 2,4-D prevented deesterification of diclofop-methyl to diclofop. Qureshi and VanderBorn (165) observed a similar effect with MCPA and diclofop-methyl. Todd and Stobbe (197) concluded that degradation of diclofop-methyl to diclofop was necessary because diclofop was responsible for translocating to and inhibiting the growth of meristematic tissue. Herbicide antagonism can often be overcome by increasing the rate of graminicide and/or decreasing the amount of broadleaf herbicide in a tank-mix (12, 42, 61, 98, 102, 128, 136, 144, 149, 150, 202, 210). At a constant diclofop rate of 2.2 kg/ha, wild oat control decreased from 87% to 82, 70, 63 and 54% as MCPA rates increased from 0.15 to 0.3,(L6 and 1.1 kg/ha, respectively (150). Wild oat control was improved with an increase in diclofop rates (150). However, the added cost of increasing herbicide rates may make tank-mixing uneconomic (150) 30 Some researchers have determined that separating the application of the broadleaf and grass herbicide by a few hours to a few days, would reduce or remove the antagonism on weeds as well as crop injury (16, 58, 59, 61, 63, 83, 98, 109, 128, 149). For example, wild oat control with diclofop was not affected by MCPA, if MCPA.was applied two days before or one day after diclofop (149). Split applications as close as one to two minutes apart, demonstrated 19% better control of wild oats than the tank-mix (149). Henne (98) found that seven day split applications of sethoxydim and linuron were more effective than the tank-mix. However, linuron should be applied before sethoxydim, otherwise broadleaf weeds become too large for satisfactory control. Air temperature after herbicide application can also affect antagonism (32, 150). Olson and Nalewaja (150) observed an increase in the antagonism of MCPA with diclofop as temperatures increased from 10 to 30C. Herbicidal Activity in_Soil Soil activity resulting from preemergence (pre), preplant incorporated (ppi), or postemergence applications of several graminicides can be an important grass control component (1, 13, 30, 41, 53, 64, 72, 74, 76, 86, 87, 103, 110, 130132, 142, 154, 159, 162, 172, 173, 174, 189, 190, 192, 196, 202, 217). Velovitch (200) states that generally; herbicide rates two to five times greater than recommended post rates are necessary for adequate grass control with ppi or pre applications. The present cost of grass herbicides makes soil applications prohibitive. Diclofop is one of the phenoxy-phenoxy herbicides most researched for its soil residual 31 activity. Wu and Santelman (217) found that diclofop was most phytotoxic to sensitive grass species when applied ppi or early post. Preemergence treatments were only effective if the herbicide was quickly incorporated through water. Residual activity of diclofop has been shown at a rate of 1.1 kg/ha (41). Chow (41) noted that a post application to wild oat successfully controlled 53% of the green foxtail (Setaria viridis (L.) Beauv.), which was seeded three weeks after diclofop application. Ennis and Ashley (72) demonstrated a 50% reduction in emergence of large crabgrass following diclofop applications of 1.1 and 1.7 kg/ha. One important aspect in determining the effectiveness of post versus pre applied diclofop, is the difference between root and shoot absorption (41, 52, 76, 142). Chow (41) indicated foliar applications of diclofop to wild oat reduced shoot and root growth 51 and 18~1%, respectively. Applications to the root, however, decreased shoot growth C§)5%) but increased root growth inhibition (27Q4%), when compared to foliar applications. He concluded diclofop uptake was important through both shoot and root, but was more effective in controlling wild cat when applied to the foliage. Persistence studies by Wu and Santelmann (217) found that no diclofop phytoxicity was detectable eight weeks after application under variable temperatures and 5 to 10% soil moisture. This was true of both incorporated and surface applied treatments. However, a significant reduction in herbicide dissipation occurred under low soil moisture (1.5%) and/or 1cwv soil temperature (4.4 C) (217). They suggested that soil microorganisms were responsible for herbicide decomposition. Martens (130) reported the persistence of diclofop was affected by soil type and the amount of aeration. Under aerobic 32 conditions, 50% of the diclofop activity was lost within six to nine days in sandy soil and 23 to 28 days in a sandy loam, whereas 50% decomposition under anaerobic conditions required over 150 days. Todd and Stobbe (196) determined that both tolerant and susceptible species absorbed similar amounts of 14C-diclofop and concluded differential root uptake does not explain the selectivity of this herbicide. Soil activity studies with pyridinyl oxy-phenoxy herbicides indicate differences in rates necessary for adequate control of various grass species. Himmelstein and Peters (103) found that GSA-82725 at 0.84 kg/ha completely control led large crabgrass and several perennial forage grasses, with less injury on tall fescue (Festuca arundinacea Schreb.) and perennial ryegrass. Smooth bromegrass (Bromus inermis Leyss.) was not affected. In a field experiment, Buhler and Burnside (30) compared pre applications of fluazifop and haloxyfop for control of corn, sorghum (cv. 'Rox Orange'), foxtail millet, green foxtail, oats (Avena sativa L. 'Stout'), wheat (Triticum aestivum L. 'Centurk'), and yellow foxtail, 28 days after treatment. At 0.13 kg/ha, haloxyfop partially control led most grass species and completely control led foxtail millet, green foxtail, oats, and yellow foxtail. For fluazifop at 0.13 kg/ha, some control of all species was noted, but none of the species were completely controlled. Haloxyfop and fluazifop rates of 0.25 and 0.5 kg/ha, respectively, were necessary for > 80% control of all species. A number of factors have been reported to influence the soil activity of pyridinyl oxy-phenoxy herbicides. Both field and greenhouse results by Buhler and Burnside (30) indicated fluazifop and haloxyfop were affected by seed depth. Forage sorghum (cv. 'Rox 33 Orangefl) control 28 days after pre applications decreased with increasing depths of seed placement» Increasing the herbicide rate from 0.13 to CL5 kg/ha overcame seed placement differences. Handly et al. (87) reported optimum haloxyfop residual activity required incorporation by rainfall (one to two inches) within two weeks of herbicide application. Adsorption of herbicides to soil colloids affects the leaching ability of the chemicals. Rick et al. (174) compared the soil adsorption characteristics of fluazifop, haloxyfop, and CGA-82725. They found that each herbicide had a moderate to high potential for mobility in soil. Surprisingly, adsorptioncininot correlate with either clay or organic matter content. Adsorption, however, was found to decrease as soil pH increased (174). Length of residual activity differs between fluazifop and haloxyfop (30). Buhler and Burnside (30) noted that while > 80% growth reduction of seeded forage sorghum occurred only up to 14 days after ()5 kg/ha of fluazifop was applied, similar rates of haloxyfop controlled sorghum up to 28 days after application. Haloxyfop-methyl degrades very quickly in soil to haloxyfop (half-life = 24 h) (64) Haloxyfop, however, has an average half-life of 55 days (64). Stonebridge (192) found that fluazifop preemergence activity was expressed for 3 to 12 weeks. Pre applications of both fluazifop and haloxyfop demonstrated significantly greater herbicide uptake by emerging forage sorghum in the root zone, as compared to the shoot zone (30). However, Buhler and Burnside (30) indicated that absorption from soil was not an important control component when making postemergence applications to sorghum. 34 Preemergence activity of sethoxydim is variable and requires higher rates than necessary for adequate postemergence control (132) Buhler and Burnside (30) reported that 1.0 kg/ha sethoxydim, applied pre, controlled green foxtail, yellow foxtail, and oats > 70%, but had little effect on corn, forage and grain sorghum, foxtail mil let, or wheat. Ennis and Ashley (72) observed poor preemergence control of large crabgrass with sethoxydim at 0.56 kg/ha. However,lfinmmlstein and Peters (103) concluded that CL28 kg/ha of sethoxydim applied pre, provided adequate control of large crabgrass and several perennial forage grasses. Preemergence activity of sethoxydim was significantly affected by seeding depth (30). Buhler and Burnside (30) found sethoxydim rates of 0.2 and 0.4 kg/ha control led forage sorghum seed laying on the soil surface, but placement of seed up to six cm in the soil resulted in only a 28% reduction in growth. Similar to the pyridinyl oxy-phenoxy herbicides, sethoxydim is readily absorbed by roots (30). Ennis and Ashley (74) stated that lower concentrations of sethoxydim on large crabgrass were necessary for root applications than for shoot applications. These differences were primarily associated with differential absorption rates between roots and foliage. Adsorption studies by Hsiao and Smith (110) indicated sethoxydim activity was similar in sandy loam, clay loam, and heavy clay soils. McAvoy (132) estimated the soil half-life of sethoxydim was only 2 to 13 days. Although many factors are involved in influencing the soil residual activity of the selective grass herbicides, Velovitch (202) warns that minimal activity can occur when postemergence applications are made to dense populations of grasses. It is important that 35 herbicides targeted for postemergence control also reach the soil surface. Fate in Plants Absorption. A significant characteristic of many of the postemergence grass herbicides is their rapid absorption through the foliage of monocots (28, 56, 79, 122, 132, 135, 142, 157, 186, 196, 201, 202, 214, 215). McAvoy (132) reported that one hour after treatment, grasses had taken up the majority of sethoxydim applied. In radiolabel studies conducted by Derr et al. (56), radioactivity was detected in all [alant parts of three annual grass species six hours after VAC-fluazifop was fol iarly applied. Buhler et al. (28) noted that haloxyfop uptake by the susceptible grasses shattercane (Sorghum bicolor (L.) Moench) and yellow foxtail, as well as tolerant soybean, was almost complete within 48 h of treatment. The absorption of post-applied graminicides appears to be a function of environment, retention on the foliage, and adjuvant. Moisture stress effectscniherbicide uptake have generally'not been significant. Dortenzio and Norris (62) discovered that water stress did not reduce the absorption of diclofop. Akey and Morrison (2) noted a significant reduction in diclofop penetration into wild oat leaves at a gravimetric soil moisture content of 10% as compared to 20%, 6 h after herbicide application; however, the difference was negligible 12 h after application. They concluded that the short-term differences in rate of uptake of diclofop could not entirely account for the variation in activity between the soil moisture content. For a perennial grass such as johnsongrass, Rosser et al. (179) found that absorption of 14C fluazifop 24 or 72 h after treatment was not reduced by moisture 36 stress. Radioautographs by Kells (120) suggested a greater amount of 14C-fluazifop in quackgrass which was not moisture stressed, but the difference was not significant. With a number of different herbicides, relative humidity (RH) is important in influencing penetration. McWhorter and Wills (133) reported a large effect of RH on 14C-mefluidide uptake into johnsongrass. In the absence of an adjuvant, an increase in RH from 40 to 100% resulted in a five- to six-fold increase in the uptake of 14C- mefluidide. McWhorter and Wills (133) noted a general increase in absorption of 14’C-mefluidide into soybean and common cocklebur (Xanthium pensylvanicum Wal 1r.) with an increase from 40 to 100% RH. Relative humidity also influenced 14C-sethoxydim uptake in bermudagrass (215). Wills (215) demonstrated that absorption of the radiolabelled herbicide was greater at 100% than 40% RH. 1 Air temperature at the time of treatment can also influence the penetration of the postemergence grass herbicides. McWhorter and Wills (133) found that 14C-mefluidide absorption into johnsongrass, without an adjuvant, was increased, but less than two-fold, as the air temperature was raised from 22 c to 32 c. In addition, 14c-mefiuidide absorption, without an adjuvant, was increased two-fold in common cocklebur and up to three-fold in soybean at temperatures of 32 C compared to 22 C. Radiotracer studies conducted by Kells et al. (122) revealed 14C-fluazifop absorption into quackgrass was significantly greater at 30 c (71.47. of applied 140) than at 20 c (45.37.) Along with environmental factors, spray retention and placement on the target species could also affect herbicide activity. Todd and Stobbe (196) noted that green foxtail retained larger amounts of spray 37 solution containing diclofop than wheat (cv. 'Neepawa'), barley (cv. 'Bonanza'), or wild oat. Green foxtail is more sensitive to diclofop than the other three species, when sprayed at a smaller stage of growth, which may be attributed in part, to greater spray retention. Todd and Stobbe (196) related the retention differences to the horizontal arrangement of green foxtail's first two leaves, as opposed to the erect growth habit of seedlings from the other species. This implies that green foxtail's uptake site area is larger than the other species. Wild oat is also sensitive to diclofop at early growth stages, but retained the least spray solution of the four species (196). Boldt and Putnam (23) did not find spray retention to be a primary selectivity mechanism between susceptible and tolerant species. Their research indicated that soybean (cv. 'Hark') and cucumber (Cucumis sativus L. 'Green Star'), both tolerant to diclofop, retained similar amounts of chemical as barnyardgrass, a sensitive species. However, in the same study, they noted that wild proso millet, a moderately sensitive species to diclofop, retained 3 to 10 times more chemical on a ug/mg dry weight or pg/cm2 leaf area basis than soybean, cucumber, longspine sandbur (Cenchrus longispinus (Hack.) Fern.), or barnyardgrass. This may have resulted from proso mil let's pubescence and partially explains its susceptibility. Placement of the herbicide near the apical and meristematic regions of the plant has also been reported to increase the efficacy of graminicides (107, 186). This may be related to less development of waxy layers and cuticle on newly developing tissue. Nalewaja et al. (142) reported that diclofop applications were more effective when 38 applied close to meristematic tissue, such as the ligule, than to various other areas along a leaf. Friesen et al. (76) also stated that applications of diclofop near the stem apex of wild oat plants, resulted in the most effective control. They concluded that adequate control of dense wild oat populations require thorough spray coverage, because of the many leaf blades which could shield the meristematic regions of the plant. Translocation. IWanycfiithe postemergence grass herbicides are xylem and phloem mobile, and readily translocated to meristematic regions in shoots, roots, and rhizomes (21, 56, 81, 122, 132, 135, 157, 162, 178, 192, 200, 202, 215, 216). Numerous studies have demonstrated that translocation of graminicides through time varies among herbicides and species (21, 28, 55, 122, 202, 206). Waldecker and Wyse (206) found a differential rate of translocation between sethoxydim, KK-80, and RO-l3-8895. Complete rhizome bud kill of quackgrass was achieved when sethoxydim at a rate of'()6 kg/ha was allowed to translocate one day. However, at the same chemical rate, bud viability was not significantly reduced until RO-13-8895 and KK-80 were allowed to translocate 7 and 14 days, respectively. Bloomberg and Wax (21) noted the rate and quantity of mefluidide translocated, varied between giant foxtail, (Setaria faberi Herrm.), common cocklebur, and soybean. One day after treatment, giant foxtail translocated approximately 12% of the 14C-mefluidide applied out of the treated leaf, but common cocklebur and soybean had only translocated l to 2%. After eight days of treatment, common cocklebur and soybean translocated a maximum of 29.7 and 20.2%, respectively, of the VAC-mefluidide applied, but giant foxtail had only translocated 16.8% after six days. 39 The actual translocation of labelled graminicides throughout various species is often small (2, 23, 92, 122, 135, 186, 193, 202). McWhorter (135) discovered that 14C-metriflufen activity was found in all parts of johnsongrass and soybean 48 h after application, but less than 1% of the 14C-metriflufen translocated out of the johnsongrass treated leaf, and only 2 to 11% translocated out of the treated soybean leaf. Shimabukuro et al. (186) reported that only 3 and 7% of the 14C- diclofop applied to excised shoots of wheat (cv. 'Waldron') and wild oat, respectively, were translocated to the upper blades. Kells et al. (122) observed that translocation of 14C-fluazifop 6 h after treating quackgrass and soybean leaves, was only 1.5 and 2.3% of the chemical applied, respectively. After 144 h, the amount of 14C—f1uazifop translocated from the treated leaf of quackgrass and soybean was 14.1 and lEL5%, respectively. Although the amount of chemical translocated from foliage to the proposed site of action in many grasses is relatively shall, it is often adequate to kill the plant. In some instances, the growth stage of the treated grass has affected the translocation, as well as uptake, of the applied herbicide. Derr et al. (56) detected more rapid absorption and higher concentrations of 14C-fluazifop throughout large crabgrass and giant foxtail plants treated at pre-tillering, as compared to tillering plants. The ability of large crabgrass and giant foxtail to tolerate more fluazifop at later growth stages could be partially explained by absorption and translocation differences. Kells et al. (122) conducted radiotracer studies with 14C-fluazifop on two- to three- and five- to six-leaf quackgrass. Although quantitative translocation differences between quackgrass plants at the two growth stages were not 40 significant, radioautographs indicated that herbicide translocation was more extensive in quackgrass treated at the the two- to three-leaf stage. Kel ls et al. (122) suggested that these translocation differences could partially explain the poorer control of five- to six- leaf quackgrass. Environmental factors such as moisture, air temperature, relative humidity, and light may also influence translocation (2, 122, 133, 135, 166, 179, 214, 215). Ready and Wilkerson (166) measured the regrowth of normal and drought stressed johnsongrass, which had been treated with fluazifop. Foliage of johnsongrass was removed at certain intervals after treatment. Fluazifop translocation into the rhizomes was faster in non-stressed plants. McWhorter (135) found that translocation of 14C-metriflufen in johnsongrass was twice as great at 27 c as at 18 c, and 17% higher at 35 0 than at 27 c. McWhorter and Wills (132) reported that increasing the relative humidity from 40 to 100% under two temperatures resulted in a 33 to 49% increase in the translocation of l4C-mefluidide in johnsongrass. Light has also been shown to affect chemical translocation. Radiotracer studies on quackgrass by Kells et al. (122), indicated 14C- fluazifop was translocated 1739 and 14.1% respectivelyu under full light as compared to shade. This suggests 14C-fluazifop translocation is promoted by conditions favoring photosynthate movement. Although many environmental and physiological factors influence the absorption and translocation of the postemergence grass herbicides, differential absorption and translocation does not appear to be their primary selectivity'mechanism (21, 23, 79, 122, 133, 161, 178, 193, 196, 202, 214). Rosser et al. (178) noted that tolerant sunflower 41 (Helianthus annuus L.) and susceptible johnsongrass absorbed similar amounts of 14C--f1uazifop, yet sunflower translocated significantly more 14C-herbicide than johnsongrass. Boldt and Putnam (23) found similarities in absorption of diclofop and its limited, yet similar translocation in five tolerant and susceptible species. The magnitude of tolerance expressed by broadleaf plants could not be eXplained by differences in absorption and translocation. Metabolism. Although the site of action of the postemergence grass herbicides is generally agreed upon, the mode of action is less well understood. Generally, tolerant species remove the active compounds from plant cells more quickly and completely than susceptible species. This removal is done by either conjugating the herbicides with proteins or sugars, or breaking down the active molecules into inactive metabolites. The most extensive research on the metabolism of a graminicide has been with diclofop (2, 24, 81, 84, 186, 216). The selectivity of diclofop appears to depend on the differential metabolism between tolerant and susceptible species (24, 84, 186). Shimabukuro et al. (186) proposed a scheme to explain the metabolic fate of diclofop in wheat (cv. 'Waldron‘) and wild oat (Figure 2). The initial metabolism of the applied diclofop-methyl, within each species, is the hydrolysis of the parent molecule to its acid form (diclofop), which is also phytotoxic. At this point, wheat irreversibly detoxifies diclofop through an aryl hydroxylation to what is termed ring-OH diclofop. The ring—OH diclofop can undergo a reversible reaction and be converted to a non-toxic phenolic conjugate. In wild oat, on the other hand, it undergoes a reversible reaction where the diclofop is converted to an ester conjugate through glycosyl ester conjugation. Figure 2. 42 Proposed metabolism of diclofop-methyl in wheat and wild oats(l86) 43 ‘Q—M-@- O-C-COOCH3 (ocflve) @11 wheat a wild oat CH3 0 @o-c-coow , CI‘Q- (octwe) Cl whe/ wild oat OH (EH C O @O-g-COOHPQ C '-@-OO-C-COOR (inactive) (inactive) \ CIC§O CH3 «@4 O-C- COOH H (inactive) (A 44 The ester conjugate can act as a readily available pool for diclofop; ester hydrolysis can reform diclofop. Shimabukuro et al. (186) stated that the mode of action of diclofop-methyl involves growth inhibition and ultrastructural cell damage. Other research (Shimabukuro et al., 1978 (185)) suggests that growth inhibition could be caused by diclofop-methyl, and ultrastructural cell damage may be caused by diclofop. Studies conducted by Boldt and Putnam (24) confirm the scheme of Shimabukuro et al. (186). Five tolerant and susceptible plants converted diclofop-methyl to diclofopu Acid hydrolysis of plant extracts revealed larger amounts of ring-OH diclofop in tolerant species, suggesting metabolism of diclofop similar to that which occurs in wheat (24). Swisher and Corbin (193) proposed that the difference in tolerance to sethoxydim between johnsongrass and soybean (cv. 'Coker 1560, was related to the inability of johnsongrass to transform sethoxydim to a non-toxic metabolite as quickly as soybean. Velovitch (202) found that the metabolism of fluazifop-butyl in foxtail millet and common cocklebur yielded the parent acid, fluazifop. ‘This occurred through hydrolysis of the n-butyl side chain. The rate of hydrolysis is faster in foxtail mil let than in common cocklebur, but is not the selectivity'mechanism explaining differential tolerance. .M9g2.9:_gggflggy One mode of action of fluazifop is proposed to be interference with adenosine tri-phosphate (ATP) production (162). Velovitch (202) found that meristematic ATP levels in foxtail millet were initially suppressed (6 h), then increased to levels 162% above that in control plants, 12 h after treatment. After 96 h, ATP levels were only 50% that of control plants. Common cocklebur fol lowed a similar trend as foxtail millet, except that a peak in ATP level 45 occurred at 3 h after treatment with a rapid decline thereafter. Velovitch (202) concluded that altering meristematic ATP levels was not a mechanism for the:mode of action of fluazifop, and instead that it impaired same plant process which resulted in a rapid accumulation of ATP. Protein synthesis is one plant process which requires much ATP. Peregay and Glenn (160) radiolabelled the amino acid leucine and reported that fluazifop inhibited the incorporation of leucine into protein. They demonstrated that fluazifop, at a concentration of 10'4M, reduced protein synthesis in both corn and soybean coleoptiles by 56 and 64%, respectively, compared to controls. At 10’5M concentrations, fluazifop stimulated soybean protein synthesis by 59%. Even though differences in selectivity of the postemergence grass herbicides exist, many of the injury symptoms are similar (81, 107, 114, 157, 192, 200). Jain and VandenBorn (114) reported inhibition of internode elongation of wild oat plants within two days of sethoxydim and within five days of fluazifop and haloxyfop application. Injury symptoms throughout the 14 days following herbicide application included: constriction and necrosis at the base of the internode closest to the apex, disruption and necrosis of epidermal tissue, and deformation of parenchyma cells to an amoeboid shape. Injury was most severe in the cortical meristematic cells (114). Along with leaf chlorosis and subsequent necrosis, shoot tissue can also undergo pigment changes, characteristic of anthocyanin synthesis and senescence. Under favorable growing conditions, injury symptoms appear on target grasses within five to seven days. Cool temperatures and/or low soil moisture can delay the period for one to two weeks. Late fall applications may require several weeks before grasses are significantly 46 injured. Gealy and Slife (78) noted that damage to grass meristematic tissue was not the only injury symptom resulting from the grass herbicides. After the initial leaf growth inhibition following application of sethoxydim, difenopenten, and diclofop, a significant reduction in corn leaf photosynthesis occurred. Beardmore et al. (14) determined that postemergence applications of lethal concentrations of haloxyfop, fluazifop, and sethoxydim, significantly reduced water uptake by oats, but not until 10, 13, and 17«days after application, respectively. Although many systems are ultimately affected, it is unlikely that the initial site of action sensitive to the lowest concentration of graminicides have been determined. There may be different sites for each particular compound. LITERATURE CITED Abernathy, J. R., 8. Bean, and J. R. Gipsan. 1983. Soil and foliar activity of selective grass herbicides. Abstr. Weed Sci. Soc. Am. p. 31. Akey, W. C. and I. N. Morrison. 1983. 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Richardson, W. G., T. M. West, and C. Parker. 1980. The activity and postemergence selectivity of some recently developed herbicides: R 40244, DPX-4189, acifluorfen, ARD 34/02 (NP 55) and PP009. Tech. Rep. Agr. Res. Council Weed Res. Org. 61, pp. 41- 52. Richardson, W. G., T. M. West, and C. Parker. 1981. The activity and preemergence selectivity of some recently developed herbicides: UBI S-734, SSH-43, ARD 34/02 (= NP 55), PP009 and DPX 4189. Tech. Rep. Agr. Res. Council Weed Res. Org. 62, pp. 35-43. Rick, S. K., F. W. Slife, and W. L. Banwart. 1983. Residual activity of selective grass herbicides. Proc. North Central Weed Control Canf. 38:1. 174. 175. 176. 177. 178. 179. 180. 181. 67 Rick, S. K., F. W. Slife, and W. L. Banwart. l984. Adsorption of selective grass herbicides by soil. Abstr. Weed Sci. Soc. Am. p. 97. Ritter, R. L. and T. C. Harris. 1981. Interactions of postemergence soybean herbicides. Proc. Northeastern Weed Sci. Soc. 35:63. Robinson, R. R., S. R. Colby, and A. A. 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North Central Weed Control Conf. 36:116. Slack, C.1L and W.)L Witt. 1983. Herbicide applications with CDA. Abstr. Weed Sci. Soc. Am. p. 54. Smith, A. E. and A. I. Hsiao. 1983. Persistence studies with the herbicide sethoxydim in prairie soils. Weed Res. 23:253-257. 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 braadleaved crops. Abstr. Weed Sci. Soc. Am. p. 107. 191. 192. 193. 194. 195. 196. 197. 198. 69 Souza, M. V., A. Ali, and E. N. Knibbe. 1983. Onion III barley wind abatement, 1983. Expert Committee on Weeds, Eastern Canada Section, Res. Rep. p. 284. Stonebridge, W.CL 1981. Selective post-emergence grass weed control in broad-leaf arable craps. Outlook on Ag. 10:385-392. Swisher, B. A. and F. T. Corbin. 1982. Behavior of BAS-9052 OH in soybean (Glycine max) and johnsongrass (Sorghum halepense) plant and cell cultures. Weed Sci. 30:640-650. Teitz, A. Y., R. D. Ilnicki, and C. Kupatt. l984. Weed control an soybeans with various preemergence and postemergence herbicides. Proc. Northeastern Weed Sci. Soc. 38:28-33. Therkilsen, J. A., M. K. Ekeh, W. H. Palmer, and J. P. Herberger. 1981. Fluazifop (PP-009): control of quackgrass in soybean in the north central region. Proc. North Central Weed Control Conf. 36:112-113. Todd, B.(L and E.1L Stobbe. 1977. Selectivity of diclofop- methyl among wheat, barley, wild oat (Avena fatua) and green foxtail (Setaria viridis). Weed Sci. 25:382-385. Todd, B. 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. Tripp, T. N. and P. A. Banks. 1983. Comparison of sethoxydim and fluazifop-butyl for large crabgrass (Digitaria sanguinalis (L.) ScopJ control as affected by growth stage and tank mixtures. Abstr. Weed Sci. Soc. Am. p. 30. 199. 200. 201. 202. 203. 204. 205. 206. 70 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. Velovitch, J. J. 1982. New postemergence herbicides for controlling grass weeds in soybeans. Weeds Today. 13(2):12, 17- 18. Velovitch,1L J.andlfi W.Slife. 1982. Uptake,translocation, and metabolism of fluazifop-butyl in graminaceous and dicotyledonous plants. Proc. North Central Weed Control Conf. 37:58. Velovitch, J. J. 1983. Studies on postemergence grass herbicides for soybeans and uptake, translocation and metabolism of fluazifop-butyl in several plants. Ph.D. Dissertation, Univ. of Illinois at Urbana-Champaign. 115 pp. Vitolo, D. 8., R. D. Ilnicki, M. W. Beale, and P. Chitapong. l984. Oxyfluorofen in combination with several grass herbicides in transplanted cole crops. Proc. Northeastern Weed Sci. Soc. 38:106-112. Wagner, V. and G.¢) Letendre. 1982. Postemergence quackgrass [Agropyron repens UN) Beauvgl control in broadleaf crops with TF l 169 (butgfl 2-[4-(5-trif1uaromethyl-Z-pyridyloxy) phenoxy) propionate) in eastern Canada. Abstr. Weed Sci. Soc. Am. p. 18. Wagner, V. 1983. Postemergence quackgrass control in broadleaf crops with fluazifop-butyl in eastern Canada. Proc. Northeastern Weed Sci. Soc. 37:95-96. Waldecker, M. A. and 0.1" Wyse. l984. Quackgrass (Agropyron ggpggg) control in soybeans (Glycine max) with BAS 9052 OH, KK-BO, and R0-13-8895. Weed Sci. 32:67-75. 207. 208. 209. 210. 211. 212. 213. 214. 71 Webber. C. L., M. R. Gebhardt, and L. F. Bouse. 1983. Use of the CDA for applying herbicides with soybean oil. Proc. North Central Weed Control Conf. 38:127. West, L. 0., J. H. Dawson, and A. P. Appleby. 1980. Factors influencing barnyardgrass (Echinochloa crus-galli) control with diclofop. Weed Sci. 28:366-371. Willard, T. R., W. L. Currey, and M. D. K. Owen. 1983. Tolerance of three St. Augustine grass cultivars and centipede-grass to sethoxydim and fluazifop-butyl. Proc. South. Weed Sci. Soc. 36:128. Williams, C. S. and L. M. Wax. 1983. The interaction of bentazon and haloxyfop or sethoxydim. Proc. North Central Weed Control Conf. 38:41. Williams, C. S. and L. M. Wax. 1984. The interaction of bentazon and haloxyfop-methyl or sethoxydim. Abstr. Weed Sci. Soc. Am. p. 6. Williams, R. D. 1984. New postemergence grass herbicides highlighted. Pacific Northwest Weed Topics. 84-122-3. Wills, G. D. 1981. Effect of environment an the toxicity of BAS- 9052 [2-(N-ethaxybutyrimidoyl)-5-(2-ethylthiopropyl)-3-hydroxy-2- cyclohexen-l-one] and KK-80 (ethyl-4-[4-[4-(trif1uoromethyl) phenoxy]phenoxy]-2-pentenoate] to common bermudagrass (Cynodan dactylon L.). Abstr. Weed Sci. Soc. Am. p. 9-10. Wills, G. D. and P. M. Jordan. 1981. Factors affecting toxicity and translocation of metriflufen in cotton (Gassypium hirsutum). Weed Sci. 29:308-313. 215. 216. 217. 218. 72 Wills, 0.0. 1984. Taxicity'of translocation of sethoxydim in bermudagrass (Cynodon dactylon) as affected by environment. Weed Sci. 32:20-24. Worthing, C. R., W. G. Richardson, and W. A. Taylor. 1982. Herbicides and their properties. I3 H. A. Roberts (ed.) Weed Control Handbook: Principles. Blackwell Scientific Publications, Oxford, England. pp. 152-154. Wu, Chu-huang and P. W. Santelmann. 1976. Phytotoxicity and soil activity of HOE-23408. Weed Sci. 24:601-604. Young, R. S. 1982. Quackgrass control with fluazifop-butyl. Proc. Northeastern Weed Sci. Soc. 36:183-184. CHAPTER 2 ‘RESPONSE OF SELECTED ANNUAL GRASSES AND CEREAL CROPS TO FOLIAR APPLICATIONS OF FLUAZIFOP-BUTYL ABSTRACT Field studies were initiated to determine the response of selected annual grasses and grain crops to fluazifop-butyl ((:)-butyl 2-[4-([5- (trif 1 uoromethyl )-2-pyridinyl] oxy)phenoxy] propanoate). The sensitivity of large crabgrass (Digitaria sanguinalis (L.) Scop.), giant foxtail (Setaria faberi Herrm.), green foxtail (Setaria viridis (L.) Beauv.), yellow foxtail (Setaria lutescens (Weigel) Hubb.), and Japanese millet (Echinochloa crusgalli var. frumentacea (Roxb.)) decreased with increasing plant age. Response to specific rates varied between two years but indicated the decending order tolerance to fluazifop-butyl was: green foxtail > large crabgrass > yellow foxtail > giant foxtail _>_ Japanese millet. Phytoxicity to oats (Avena sativa L. ‘Gary'), rye (Secale cereale L. 'Wheeler'), wheat (Triticum aestivum L. 'Yorkstar'), and sorghum (Sorghum bicolor (L.) Moench 'Bird-a-boo') was also more pronounced on younger plants with the latter two species extremely sensitive. Correlations of grass biomass with visual ratings for annual grasses and grain crops suggest that grass biomass is often an unreliable indicator of control. 73 INTRODUCTION The recent introduction of fluazifop-butyl and several other graminicides, has provided weed control options not found with preplant incorporated or preemergence herbicides. Although this flexibility includes numerous annual grass species and wide ranges of timing of application, large differences exist among graminicides in rates required for control of different species (3, 4, 6, 7, 11, 21, 23, 24). Buhler (7) reported control of sorghum by sethoxydim (2-[1- (ethoxyimino) buty11-5-[2-(ethylthio) propyl]-3-hydroxy-2-cyclohexen-l- one), haloxyfop-methyl (methyl-[4-([3-chloro-5-(trif1uoromethyl)-2- pyridinylloxy)-phenoxy]propanoate), and fluazifop-butyl. However, more than three times the amount of fluazifop-butyl and six times more sethoxydim were required compared to haloxyfop-methyl. Diclofop-methyl (methyl 2-[4-(2,4-dichlorophenaxy)phenoxy]pro- panoate acid), the first of many structurally related compounds, controls a limited number of species, but more importantly, has a narrow 'window' for time of application (one- to four-leaf stage) (2, 9, 12, 19, 28, 30, 32) The more recently introduced graminicides also appear to be less effective as grasses mature (see Chapter 1, p. 14). Drew (10) found that fluazifop-butyl control led selected annual grasses and small grains at emergence and in the seedling stage, but higher rates were required when grasses matured. 74 75 Grain crops sensitive to the new postemergence graminicides include wheat, oats, rye, and sorghum (5, 6, 7, 10, 16, 25, 26). In two separate experiments, Brewster (5, 6) reported good to excel lent control of the previously mentioned crops with fluazifop-butyl at a rate of 0.25 lb/A. The purpose of this study was to (a) compare the susceptibility of five annual grasses at three stages of growth to fluazifop-butyl, and (b) determine the effectiveness of fluazifop-butyl on four grain crops, each at two different stages of growth. Knowledge of the sensitivity of grain craps is important in cropping systems which utilize them as tools for weed management and/or erosion control. MATERIALS AND METHODS Greenhouse Investigations Greenhouse experiments were conducted in the fall of 1983 to compare the susceptibility of Japanese millet and barnyardgrass (Echinochloa crusgal 1i (L.) Beauv.). This information was needed to justify the use of Japanese millet as an indicator in the annual grass susceptibility studies. Grasses were grown in perforated 975 ml (12 cm diameter) plastic cups containing a soil mix of 3:1 Spinks loamy sand to peat-perlite (pH 6.2-6.4). Natural light was supplemented (14 h) with metal halide lighting at an average photosynthetic photon flux density (PPFD) of 290 umol°s‘1°m'2. Grasses were fertilized one to two times per week with approximately 50 ml of a soluble fertilizer (Peters 20-20-20, 1 g/l). Herbicides were applied to grasses (three to four per cup) with five fully expanded leaves. A leaf was defined as fully 76 expanded when the collar was present. Thiautomated air pressurized moving belt sprayer was used to deliver the herbicide through an 8001 E flat fan nozzle at a volume of 337 L/ha and a pressure of 235 kPa. Each grass species was treated with formulated fluazifop-butyl (4 EC) at rates of 0.0175, 0.035, 0.07, 0.14, and 0.28 kg/ha. Included in all treatments was a petroleum based crop oil concentrate (80:20 petroleum oil to emulsifiers*) on a 0.7% v/v basis. Treated plants were grown for 14 days in the greenhouse under mean daily temperatures of 24 to 27 C and 70% relative humidity (RH), and mean night temperatures of (20 to 22 C) and 90% RH. After 14 days, injury ratings (0 = no effect, 10 = complete kill) were made and plants harvested for dry weight determination. Dry weights were recorded after drying at 55 C for four to six days. The factorial experiments (6 rates x 2 species) were performed using a randomized complete block (RCB) with four replications. Results of two experiments were combined and analyzed by Fisher's least significant differences test at the 1% level. Field Investigations General Procedures for Annual Grass Studies. All field experiments were conducted at the Horticulture Research Center at East Lansing, Michigan. In both 1983 and 1984, five species consisting of green, yellow, and giant foxtail, large crabgrass, and Japanese millet were utilized. Prior to planting, grass seed were vernalized for one month at -18 C fol lowed by two to three weeks at 2 C. Grasses were *Torch crop oil concentrate, manufactured by Torch Chemicals, Division of Amoco Oil Company, Chicago, IL. 77 seeded using a mechanical planter which evenly distributed a given volume of seed into five rows (spaced 15.2 cm apart) over a distance of 7.7 m. Individual plot sizes were 1.4 by 1.9 m. Overhead irrigation (an average of 1.3 cm per application) was applied as necessary. Growth stages at which applications of 0.07, 0.14, and 0.28 kg/ha of fluazifop-butyl were made, included: three-leaf (Stage I), five-leaf (Stage II), and seven-leaf (Stage III) grasses. Climatic conditions and dates of application for each treatment are listed in Tables 1 and 2. All treatments included a petroleum based crop oil concentrate on a 0.7% v/v basis. Herbicide applications were made with a C02- pressurized backpack sprayer, calibrated to deliver 337 L/ha at 262 kPa. The 1.5 m boom was equipped with three 8004 regular flat fan nozzles an 51 cm spacings. Injury ratings were made 21 days after herbicide application. Also, foliage from 31 cm of two adjacent rows were harvested for dry weight estimates. Samples were dried four to six days at 55 C and weighed. The design of this experiment was a RCB containing three factors with a split and four replications. The main plot included grass species, with growth stage and chemical rate variables randomized within each species. Grass Study, 1983. The soil type utilized for this study was a Marlette fine sandy loam. Seed from large crabgrass (12 g per plot (1.5 x 1.9 m)), green (12 9), yellow (14 g) and giant foxtail (7 g) were planted June 24. Japanese millet was planted July 1 with a single row planter at a rate of 2 g per plot. Broadleaf weeds were controlled with a broadcast application of 1.12 kg/ha 2,4-D((2,4-dichlorophenoxy) acetic acid) on July 16 and 0.84 kg/ha nitrofen (2,3-dichloraphenyl p- nitrophenyl ether) on July 25. Climatic conditions on July 16 78 Table l. Climatic conditions and dates of herbicide application for the five species in the 1983 annual grass study. . . c a Growthb Env1ranmental Conditions Date Species Stage Air T RH Wind Sail T Soil Sky (%) (mph) 7/07 Yeft, Grift, I 22 C 59 2-4 SW 21 C dry clear Gift, Lacg . 7/09 Jami I 25 C 60 4-6 NE 27 C dry clear 7/11 Gift, Grft II 26 C 76 0-1 SW 28 C dry p. cloudy 7/14 Lacg, Jami, II 23 C 92 1-3 SW 24 C moist clear Yeft 7/18 Gift, Grft III 30 C 52 2-3 NW 29 C moist cloudy 7/20 Yeft, Jami III 25 C 84 0-1 SW 29 C dry clear 7/22 Lacg III 29 C 60 4-6 SE 31 C. moist clear aYeft, Grft, Gift, and Lacg are NCWCC approved abbreviations; Jami = Japanese millet. bStage I = 3-leaf, II = 5-leaf, 111 = 7-leaf. CT = temperature, RH = relative humidity, mph = miles per hour. 79 Table 2. Climatic conditions and dates of herbicide application for the five species in the 1984 annual grass study. . . . c Growthb EnV1ronmental Cond1t1ons Date Species Stage Air 1 RH Windf Soil 1 Soil Sky (‘34) (mph) 7/01 Jami I 15 C 90 calm 14 C moist clear 7/02 Grft I 27 C 50 3-5 SW 27 C moist p. cloudy 7/02 Gift I 20 C 92 3-5 W 20 C moist cloudy 7/05 Yeft I 17 C 74 calm 21 C dry clear 7/06 Jami, Grft II 18 C 91 3-5 W 18 C moist cloudy 7/10 Gift II 26 C 72 3-5 SE 24 C moist clear 7/12 Yeft II 20 C 86 calm 23 C moist clear 7/14 Jami III 22 C 80 2-4 SW 21 C moist clear Lacg I 7/16 Grft III 18 C 76 calm 23 C moist clear 7/18 Gift III 17 C 78 0-2 NW 22 C moist clear 7/21 Lacg II 20 C 92 0-2 SW 22 C moist . cloudy Yeft III 7/28 Lacg III 23 C 52 3-5 NE 24 C moist clear aYeft, Grft, Gift, and Lacg are NCWCC approved abbreviations; Jami = Japanese millet. b CT = temperature, RH = relative humidity. mph = miles per hour. State I = 3-leaf, II = 5-leaf, III = 7-1eaf. 80 included: air temperature 22 C, soil temperature 23 C, 92% RH, southwest winds 0 to 1 miles per hour (mph), dry soil, and partly cloudy skies. Climatic conditions on July 25 included: air temperature 29.5 C, soil temperature 32 C, 52% RH, northeast wind 2 to 4 mph, dry soil, and clear skies. Grass Study, 1984. The soil type utilized for this study was a Brookston loam. Seed from Japanese mil let (11 g per plot (1.5 by 1.9 m)), green (12.5 9), yellow (10 g), and giant foxtail (10 g) were planted June 16. Poor germination of seeded large crabgrass resulted in replanting this species (7.5 g per plot) on June 27. Broadleaf weeds were removed by hand-weeding. Grain Crop Study. The soil type for this site was a Capac loam. Oats (cv. Gary), wheat (cv. Yorkstar), rye (cv. Wheeler), and sorghum (cv. Bird-a-boo) were planted with a single row planter on two separate dates, June 28, 1982 and July 9, 1982. Individual plot sizes were 2.1 by 7.7 m and consisted of one row of each grass species, spaced 31 cm apart. For each treatment, all four species were planted adjacently in the same order. The amount of seed planted for each species per 7.7 m of row was: oats, 40 g; wheat, 50 g; rye, 57 g; and sorghum, 60 g. Herbicide applications were made with the backpack sprayer previously described. On July 16, 1.12 kg/ha of 2,4-D was broadcast over the entire experiment to remove broadleaf weeds. Fluazifop-butyl rates of 0.07, 0.14, and 0.28 kg/ha were applied to each grass species on July 26, corresponding to 28 days after planting (DAP) for earlier planted species, and 17 DAP for later planted species. All treatments included a petroleum based crop oil concentrate on a 0.7% v/v basis. Weather conditions at the time of fluazifop-butyl application included: air 81 temperature 29 C, soil temperature 30.5 C, 75% RH, northwest winds 3 to 5 mph, dry soil surface, and skies mostly'cloudyu “The height of the grass species were: oats, 18 to 23 cm and 36 to 43 cm; wheat, 16 to 22 cm and 23 to 30 cm; sorghum 15 to 22 cm and 41 to 48 cm; rye, 18 to 23 cm and 23 to 30 cm. Rainfall (2.46 cm) occurred within three hours after treatments were applied. Foliage from 1.0 m of row was harvested on August 9; samples were dried for four days at 55 to 65 C and dry weights were recorded. On August 12, injury ratings for each treatment were made. RESULTS AND DISCUSSION Greenhouse Investigations Japanese-butyl millet was more susceptible than barnyardgrass at fluazifop-butyl rates of 0.07 and 0.14 kg/ha (Figure 1). However, at fluazifop rates less than 0.07 kg/ha generally used (17), no significant differences between species was observed. Also, both species were effectively control led at chemical rates of 0.28 kg/ha. Other researchers have reported adequate control of both grasses at reduced stages of growth with fluazifop-butyl rates of 0.09 to 0.14 kg/ha (3, 15, 23). This suggests that at expected chemical rates for marginal control, Japanese millet is more sensitive than barnyardgrass. Atwater and Bauman (3) reported that of seven grass species compared, barnyardgrass was more sensitive than large crabgrass, giant foxtail, yellow foxtail, and two species of green foxtail. Use of relatively uniform Japaneseinillet as a sensitive grass species, is therefore suggested as a suitable alternative for barnyardgrass (often variable 82 Figure 1. Response of barnyardgrass (Bygr) and Japanese millet (Jami) to fluazifop-butyl. 10 Mean Injury Rating 83 ‘4 \'\ OJ (LSD 0.05) I 0'1 A Jami 0 Bygr h. “ 0 0.035 0.07 0.14 0.28 Chemical Rate (Kg/Ha) 84 in germination and growth) in making comparisons of various grasses to fluazifop-butyl. Although visual injury ratings instead of dry weight data will be shown throughout, injury ratings and dry weight were highly correlated. For Japanese millet, the correlation coefficient (r) was -O.95 with the regression equation y = 0.94-.08x. For barnyardgrass, the correlation coefficient was -O.9O with the regression equation y = 0.9l-.08x. Field Investigations Grass Study, 1983. The response of each grass species to fluazifop-butyl in 1983 was affected both by the rate of chemical used and the size of grass treated (Figure 2). In general, phytotoxicity was reduced at all herbicide rates as applications to larger grasses were delayed. Within each species, there was a significant linear increase in phytotoxicity when fluazifop-butyl rates were increased for three-, five-and seven-leaf stage grasses (Figure 2, Table 3). Differences in response to fluazifop-butyl at various stages of growth, were smallest for green foxtail and large crabgrass at chemical rates of 0.07 kg/ha, and largest at rates of 0.28 kg/ha. Acceptable commercial control of these two species defined as a rating of 7.5 or above, was attained only at chemical rates above 0.14 kg/ha. This data suggests green foxtail and large crabgrass should be treated with higher chemical rates (above 0.14 kg/ha) and before grasses exceed the three- to five-leaf stage. For Japanese millet and yellow foxtail, adequate control was attained for all stages of growth with 0.14 and 0.28 kg/ha of fluazifop-butyl, respectively. Giant foxtail was relatively susceptible at both the three and five-leaf 85 Figure 2. Response of green foxtail (A), large crabgrass (8), yellow foxtail (C), giant foxtail (D), and Japanese mil let (E) to fluazifop-butyl in 1983 and 1984. 86 1983 1984 A 10 - 10 . 9 _ 1th0 0. 05) 9 _ 8 ~ 8 - A 3 eat - 0 5 . E 7 g 7 7 E a - s - E 5- 5- .: 1(LSD 0.05) t“ “ 2 A 3 Leaf 3‘ 3 " 0 5 Leaf 2 .. 2 _ X 7 Leaf 1 - 1 " L J ‘J J I J 0 0.07 0.14 0.28 0 0.07 0.14 0.28 Chemical Rate (Kg/Ha) Chemical Rate (Kg/Ha) a 10- 1°" 9 _ 1th0B 0 .05) g . .. 3 . 8 A 3 Leaf 7 .. 9 5 L 7 .- E x 7 L 22 ._ .. .5. 5~ 5' .e s 4 ~ " ” 0 E 3 __ 3 - 2 - 2 " 1 - 1 ‘ J j __J J _J _J 0 0.07 0.14 0.28 0 0.07 0.14 0.28 Chemical Rate (Kg/Ha) Chemical Rate (Kg/Ha) 87 1983 1984 C C 10 " 10 )- (LSD 0.05) 9 - 9 - B - 8 - g 7 r 7 '- 5 .. .. E 5 - 5 - «5 10.50 0.05) S 4 - 4 - a E A 3 Leaf 3 ' 3 " 0 5 Leaf 2 _ 2 _ X 7 Leaf 1 '- 1 " J _1 J I 1* J J O 0.07 0.14 0.28 O 0.07 0.14 0.28 Chemical Rate (Kg/Ha) Chemical Rate (Kg/Ha) D D 10 r 10 r L D . 8 - 8 - s 7" 7' E 5- e - I(LSD 0.05) E 5 - 5 - .5 A 3 Leaf a 4 " 4 ' O 5 Leaf g X 7 Leaf 3 '- 3 - 2 - 2 . A 3 Leaf .. 0 5 Leaf _. 1 1 X 7 Leaf J _l _l l I l O 0.07 0.14 0.28 O 0.07 0.14 0.28 Chemical Rate (Kg/Ha) Chemical Rate (Kg/Ha) 88 1983 1984 E E 10(- 10 " o - 9 - a- 8- 71- 7" £6:- 6" t 1050 0.05) E 5 - 5 ' «E A 3 Leaf s 4 _ [(1.50 0.05) 4 - e 5 L087 £1 X 7 Leaf a - 3 - A 3 Leaf 2 . 0 5 Leaf 2 . X 7 Leaf 1 - 1 ~ 9] J J 4 I J O 0.07 0.14 0.28 O 0.07 , 0.14 0.28 Chemical Rate (Kg/Ha) Chemical Rate (Kg/Ha) 89 Tab1e 3. Trend comparisons for grass response to increasing f1uazifop-buty1 rate for each growth stage. F va1ue and associated significancea Phytotoxicity response to f1uazifop rates . b c Linear Non-Iinear Spec1es Growth Stage 1983 1984 1983 1984 Grft I 81.7** 80.84** 0.22 0.08 11 64.85** 195.61** 1.09 0.75 III 14.29** 80.84** 1.52 0.08 Lacg I 73.03** 38.98** 1.3 9.17** 11 14.29** 115.33** 0.08 17.48** III 11.91** 162.24** 4.76* 0.02 Yeft I 39.0** 10.54** 4.36* 3.51 11 54.69** 59.94** 0.08 9.17** 111 70.25** 232.1** 2.03 3.51 Gift I 24.31** 0.06 4.36* 0.02 11 52.29** 8.98** 2.3 2.99 III 31.22** 56.14** 4.36* 5.32* Jami I 10.8** 14.03** 2.92 2.51 II 84.7** 0.99 2.92 0.08 III 67.52** 33.0** 3.6 1.68 aTabu1ar F va1ues for p =(101 and p 3(105 are 6.91 and 3.94, respective1y. bGrft, Lacg, Yeft, and Gift are NCWCC approved abbreviations; Jami = Japanese mi11et. cStage I = 3-1eaf, II = 5-1eaf, 111 = 7-1eaf. 90 stage. but uncontrollable at the seven-leaf stage. The relative tolerance of both seven-leaf giant and green foxtial may have been influenced by a broadcast application of 2,4-D (1.12 kg/ha), two days prior to the application of fluazifop-butyl. Although an antagonistic effect between fluazifop-butyl and 2,4-0 may have occurred, Nichols (22) did not find a reduction in large crabgrass control resulting from tank-mixing fluazifop-butyl with 2,4-0 or 2,4-08 (4-(2,4- dichlorophenoxy) butyric acid). Grass Study, 1984. Although species susceptibility to fluazifop- butyl was again substantially influenced by growth stage and chemical rate (Figure 2) in 1984, overall phytotoxicity was much greater for all species except green foxtail. This large difference in response between years may have been influenced by environmental conditions. Many of the applications in 1983 were made when soil conditions were dry. In addition, daily air temperatures throughout this experiment were consistently above 3l C. In 1984, irrigation was applied more regularly than the previous year, to insure adequate soil moisture when grasses were treated. Daily air temperatures throughout this experiment were usually between 28 and 30 C. Therefore, more favorable environmental conditions in 1984 may have enhanced fluazifop-butyl activity, compared to 1983. Akey and Morrison (1) reported wild oat plants growing under a gravimetric soil moisture content (SMC) of 20%, had 22% greater leaf area and retained 23% more diclofop-methyl than p1ants grown at 10% SMC. Similarly, the 1984 results indicated maturing grasses were more tolerant to fluazifop-butyl (Figure 2). In addition, phytotoxicity to all growth stages from each species, except three-leaf giant foxtail 91 and five-leaf Japanese millet, increased in a linear fashion with increasing fluazifop-butyl rates (Table 3). Commercially acceptable control of giant foxtail and Japanese millet was attained at herbicide rates of 0.l4 kg/ha, regardless of growth stage (Figure 2). Large crabgrass and yellow foxtail were effectively controlled at herbicide rates of 0.14 kg/ha for three- and five-leaf grasses, but required 0.28 kg/ha for seven-leaf grasses. Green foxtail was control led at chemical rates of 0.14 kg/ha only at the three-leaf stage. Adequate control of five- and seven-leaf grass required 0.28 kg/ha. Average injury ratings for each species in 1983 and 1984, indicate differences among grasses in response to fluazifop-butyl (Table 4). The relative order in tolerance to fluazifop-butyl from most to least tolerant species was: green foxtail > large crabgrass > yellow foxtail > giant foxtail 3 Japanese millet. Results of this experiment agree with the general premise that maturing annual grasses are more difficult to control with fluazifop- butyl, as well as with other graminicides (3, 8, 10, 13, 14, 15, 18, 20, 23, 27, 29). Oliver et a1. (23) regarded the stage of growth of a number of annual grasses as the most important factor influencing the activity of fluazifop-butyl and other selected herbicides. Tolerance by various species at the four- to six-leaf stage was overcome by increasing fluazifop-butyl rates, but no chemical rates tested could provide control of five- to fifteen-leaf grasses (23). However, some researchers have reported the control of giant foxtail by fluazifop- butyl was not affected by the stage of growth (24), or actually increased as the grass matured (31). Velovitch (31) reported more effective season-long giant foxtail control in soybeans (Glycine max 92 U”) MernJ, when fluazifop-butyl applications were made to five-leaf, rather than three-leaf stage grasses. He suggested that low rates of fluazifop-butyl adequately controlled small grasses,tnn:provided little soil residual activity to suppress later germinating ones. Delaying herbicide applications until grasses reached the five-leaf stage, allowed maximum germination of giant foxtail, and resulted in more effective long-term control. Velovitch (31) credited the rapid development of a crop canopy as contributing to a minimal effect of foxtail interference with soybean growth prior to fluazifop—butyl application. One should not assume, however, that delaying graminicide applications for species susceptible at advanced stages of growth is advantageous for all crops, especially those sensitive to early interference from other species. For example, Himmelstein and Peters (15) noted fluazifop-butyl significantly reduced Japanese millet, when treated at 15 to 20 and 40 cm in height, within plots of seedling alfalfa (Medicago sativa Uu)). However, yields of alfalfa at the first cut were significantly lower where grasses were permitted to compete longer. The relative order of species susceptiblity established from the data for 1983 and 1984 (Table 4), is generally in agreement with the fluazifop-butyl results of Atwater and Bauman (3). 'The only exception was that they found yellow foxtail equal to or slightly less tolerant than green foxtail, and more tolerant than large crabgrass. Although no conclusive statements regarding the stability of the order of species susceptibility can be made from the 1983 and 1984 study, it is evident significant differences in response to fluazifop-butyl exist between annual grasses. This differential response could be the result 93 Table 4. Average visual injury rating (0 = no effect, IO = complete kill) for 1983 and 1984 grass species, averaged over fluazifop-butyl rates and growth stagesa. Mean Injury Rating Species 1983 1984 Green foxtail 4.36 6.32 Large crabgrass 4.61 7.58 Yellow foxtail 5.81 8.10 Giant foxtail 6.32 9.26 Japanese millet 7.76 9.28 aTotal number of observations for each mean = 36. 94 of unique pathways of herbicide metabolism, but is more likely due to physical differences in anatomy and growth habit. Morrison and Maurice (20) attributed some of the variation in sensitivity to diclofop-methyl for two-leaf green and yellow foxtail to differences in herbicide retention. They found that green foxtail retained more than twice the amount of diclofop-methyl per gram of dry weight tissue, compared to yellow foxtail. This was despite the fact that yellow foxtail had a greater projected leaf area (20). The dense pubescence of large crabgrass leaves could have prevented a significant amount of fluazifop-butyl from reaching the leaf surface and being absorbed. Although the leaves of giant foxtail are also pubescent, these hairs are very short. They actually could have retained larger amounts of fluazifop-butyl than if leaves were glabrous, and permitted much of the herbicide to reach the surface and be absorbed into the plant. In addition, the wider leaves of giant foxtail and Japanese millet could have intercepted more fluazifop—butyl per plant than the other three species, and resulted in greater phytotoxicity. The complete explanation for species differences is not yet known. Results of the 1983 and 1984 studies were explained using visual observations of treated grasses, although dry weight data was also recorded. Correlations between dry weight data (as a percentage of control) and injury ratings, suggest that grass biomass is often a poor indicator of the actual effect of fluazifop-butyl on each species (Table 5). Visual estimates of phytotoxicity could have corrected for variability due to erratic grass germination within plots. Also, the area of foliage harvested could have been too small to accurately estimate phytotoxicity. From Table 5, it appears dry weight data and 95 Table 5. Correlation of dry weight (as a % of control) and visual injury ratings for 5 grass species in 1983 and 1984. Correlation Coefficient (r) Growth Stagea 1983 1984 Speciesb 1 II 111 I 11 III Grft —0.83 -0.23 -0.07 -0.88 -0.90 -0.76 Lacg -0.89 -0.10 -0.65 -0.88 -0.81 -0.86 Yeft —0.84 -O.72 -0.47 -0.63 -0.76 -0.74 Gift -0.85 -0.41 -0.63 -0.46 -0.62 -0.72 Jami -0.94 -0.93 -0.72 -0.79 -0.76 -0.05 aStage 1 = 3-leaf, 11 = 5-leaf, III = 7-leaf. bGrft, Lacg, Yeft, and Gift are NCWCC approved abbreviations; Jami Japanese mi11et. 96 injury ratings were more closely correlated for three-leaf than seven- leaf grasses. Smaller grasses increase in size and weight faster than larger ones. This difference could allow more distinctive and consistent weight differences to develop between fluazifop-butyl treatments for smaller grasses, and thus explain the higher correlation. Overall, this study reveals differences among grass species in response to fluazifop-butyl, and suggests that optimal control of each species at minimum chemical rates, is attained when grasses are at the three-leaf stage. Grain Crop Study. Visual observations of each species generally did not reveal a significant difference in response to fluazifop-butyl, for smal l grains treated at different dates after planting (Figure 3). Except for wheat, there was a trend toward more effective control of younger grasses. For each timing of application and grass species, except wheat at 28 DAP and sorghum at 17 and 28 DAP, there was a significant linear response to increasing fluazifop-butyl rates (Table 6). This indicates that increasing herbicide rates for oats and rye at 17 and 28 DAP, as well as wheat at 17 DAP, significantly improved grass control. However, for wheat at 28 DAP and both application timings to sorghum, effective control was most economical at chemical rates of 0.07 kg/ha. The design of this experiment violates the assumption that species are randomized between treatments, and thus prevents statistical comparisons among species. However, the intentional planting of each species in a similar order eliminated the possible variability which could have occurred as a result of differential interference by nearest neighbors. Distinct phytotoxicity differences between wheat and sorghum, and rye and oats, indicate the latter two species were more 97 Figure 3. Response of oats (A),rye (BL wheat(C), and sorghum (D) to fluazifop-butyl, l7 and 28 days after planting (DAP). 98 a 10 10v 0 (LSD 0.05) 0 - a a - A 17 DAP g 7 e 28 DAP 7 r c s ‘ I E s s - 5 g 4 4 - (LSD 0.05) O I 3 3- A 17 DAP 2 2 - e 28 DAP 1 1 - . 4 #1 J J 4 0 0.07 0.14 0.28 0 0.07 0.14 0.28 Chemical Rate (Ks/Ha) Chemical Rafe (Kg/Ha) 0 10 10 ~ A 4 9 / g _ e//‘ 8 8 h- E 7 7” g 6 5 .. E 5 5 - (LSD 0.05) 8 4 (LSD 0.05) 4 ~ g A 17 DAP 3 3 ' o 28 DAP A 17 DAP 2 o 28 DAP 2 '- 1 1 ..1 J J __| .L___J_1 J j o 0.07 0.14 0.20 0 0.07 0.14 023 Chemical Rafe (Kg/Ha) Chemical Rate (Kg/Ha) 99 Table 6. Trend comparison for grass response to increasing fluazifOp-butyl rate for each growth stage. F value and associated significancea Growth Stage Phytotox1c1ty response to fluaZifop rates Species (DAP) Linear Non-linear Oats 17 60.6*f 1.87 28 45.82** 1.37 Rye 17 41.35** 0.34 28 22.45** 0.61 Wheat 17 9.28** 0.95 28 1.83 0.61 Sorghum l7 0 O 28 1.83 0.15 alabular F values for p =<101 and p =c105 are 7.22 and 4.05, respectively. 100 tolerant. Phytotoxicity of species in this experiment was similar to results found by other researchers (4, 5, 6, 7, 21, 25). Nalewaja et al. (21) reported fluazifop-butyl applications of CL07 and 0.14 kg/ha were more phytotoxic to wheat than oats. However, this response was not similar for all graminicides tested (21). Buhler and Burnside (7) noted decreasing control of sorghum with fluazifop-butyl as the grass matured. The sensitivity of this species to fluazifop-butyl, coupled with possible differences in environmental conditions under which each experiment was conducted, could explain the non-significant response of sorghum growth stages to herbicide applications found in this eXperiment. The usefulness of dry weight data (as a percentage of control) to analyze differences among and between species, was limited due to the poor correlation with visual injury observations (Table 7). Implications for the importance of this grain crop study go beyond the need to obtain knowledge of rates necessary to control these species when they appear as weeds. with the advancement 0f conservation tillage systems and the integration of grain crops as "living mulches" for weed and erosion control in these systems, timing of application and herbicide rates which can economically and efficiently manage these grass crops, must be determined. 101 Table 7. Correlation of dry weight (as a % of control) and visual injury ratings for 4 grass species. Correlation Coefficient (r) Species Herbicide Application Timing (DAP)a (l7 ) (28 ) Oats -O.78 -0 45 Wheat -o.5o -0o56 Sorghum "Cb '0°04 Rye -0.67 -0-76 aDAP = days after planting. bNC = not calculable, due to complete kill at all chemical rates. LITERATURE CITED Akey, N. C. and I. N. Morrison. 1983. Effect of moisture stress on wild oat (Avena fatua) response to diclofop. Heed Sci. 31:247-253. American Hoechst Corp. 1976. HOE-23408, technical information bulletin. American Hoechst Corp., Agric. Division, Somerville, NJ 4 pp. Atwater, M.lfl and T.11 Bauman. 1982. Postemergent control of annual grasses in soybeans. Proc. North Central Weed Control Conf. 37:67-68. Beguhn, A. M. and M. K. Ekeh. 1982. Fluazifop-butyl (Fusilade) herbicide for control of shattercane in soybeans under emergency exemption (section 18) in Nebraska. Proc. North Central Need Control Conf. 37:83. Brewster, B. 0. 1982. New herbicides for grass control. Pacific Northwest Need Topics. 82-5:2-3. 'Brewster, B. D. 1984. Efficacy of postemergence grass herbicides. Pacific Northwest Need Topics. 84-l:4-6. Buhler, D. D. and Orvin C. Burnside. 1982. Effect of application timing on annual grass control in soybeans using fluazifop-butyl, sethoxydim, and Dowco 453. North Central Weed Control Conf. Res. Rep. 39:336-337. 102 10. 11. 12. 13. 14. 15. 16. 103 Chernicky, J. P., J. Gossett, and T. R. Murphy. 1984. Factors influencing control of annual grasses with sethoxydhn or RO-l3- 8895. Need Sci. 32:174-177. Chow, P. N. P. 1978. Selectivity and site of action in relation to field performance of diclofop. Heed Sci. 26:352-358. Drew, B. N. 1982. Postemergence fluazifop-butyl for control of grasses in oilseeds and grain legumes. Abstr. Heed Sci. Soc. Am. p. 113. Ennis, B. G. and R. A. Ashley. 1982. Effectiveness of BAS 9052 OH, diclofop and CGA 82725 applied at various stages of growth of crabgrass. Proc. Northeastern Need Sci. Soc. 36:151-153. Friesen, H. A., P. A. O'Sullivan, and N. H. Vanderborn. 1976. HOE 23408, a new selective herbicide for wild oats and green foxtail in wheat and barley. Can. J. Plant Sci. 56:567-578. Harden, J., E. Ellison, and C. Cole. 1982. Annual grass control in soybeans with sethoxydim. Proc. South. Need Sci. Soc. 35:29- 30. Higgins, E. R., C. Buchholz, M. Schnappinger, and S. N. Pruss. 1982. .Annual grass control in soybeans with CGA-82725. Proc. Northeastern Heed Sci. Soc. 37:41. Himmelstein, F. J. and R. A. Peters. 1983. Timing of postemergence grass herbicides for annual grass control in a new alfalfa seeding. Proc. Northeastern Heed Sci. Soc. 37:57-60. Hinton, A. C. and P. L. Minotti. 1983. Differential response of grass species to fluazifop and sethoxydim. Proc. Northeastern Need Sci. Soc. 37:161-162. 17. 18. 19. 20. 21. 22. 23. 24. 25. 104 ICI Americas Inc. Fusilade, experimental herbicide, technical information. ICI Americas Inc., Agric. Chemicals Div., Goldsboro, NC 4 pp. Kapusta, G. 1983. Influence of grass height and fluazifop and sethoxydim rate on giant foxtail control in soybeans, 1983. North Central Need Control Conf. Res. Rep. 40:265. Marrese, R. J. 1980. Today's herbicide: Hoelon. Needs Today. ll(4):6. Morrison, 1. N. and D. Maurice. 1984. The relative response of two Setaria spp. to diclofop. Need Sci. 32:686-690. Nalewaja, J. D., S. D. Miller, and A. G. Dexter. 1982. Postemergence grass and broadleaf herbicide combinations. Proc. North Central Heed Control Conf. 37:77-80. Nichols, R.L. 1983. Combining fluazifop and sethoxydim with 2,4-0 and 2,4-DB. Abstr. Heed Sci. Soc. Am. p. 30. Oliver, L. R., D. G. Mosier, and 0. w. Howe. 1982. A comparison of new postemergence herbicides for control of annual grasses. Abstr. Need Sci. Soc. Am. p. 17. Renner, K. A. 1983. Postemergence control of giant foxtail (Setaria faberi Herrm.) and wild proso millet (Panicum miliaceum L.) in soybeans (Glycine max (L.) Merr.), M.S. Thesis. University of Wisconsin. 162 pp. Richardson, w. G., T. M. Nest, and C. Parker. 1980. The activity and postemergence selectivity of some recently developed herbicides: R 40244, DPX 4189, acifluorfen, ARD 34/02 (NP 55) and PP 009. Tech. Rep. Agr. Res. Council Need Res. Org. 61, pp. 41- 52. 26. 27. 28. 29. 30. 31. 32. 105 Richardson, w. G., T. M. Nest, and C. Parker. 1981. The activity and preemergence selectivity of some recently developed herbicides: UBI S-734, SSH-43, ARD 34/02 (=NP 55), PP 009 and DPX 4189. Tech. Rep. Agr. Res. Council Need Res. Org. 62, pp. 35-43. Sciarappa, w. J. 1981. EUP results in the Northeast with sethoxydim. Proc. Northeastern Need Sci. Soc. 36:39-40. Todd, B.(L and E.lL Stobbe. 1977. Selectivity of diclofop- methyl among wheat, barley, wild oat (Avena fatua) and green foxtail (Setaria viridis). Heed Sci. 25:382-385. Tripp, T. N. and P. A. Banks. 1983. Comparison of sethoxydim and fluazifop-butyl for large crabgrass (Digitaria sanguinalis (L.) ScopJ control as affected by growth stage and tank mixtures. Abstr. Need Sci. Soc. Am. p. 30. Velovitch, .L. J. 1982. New postemergence herbicides for controlling grass weeds in soybeans. Needs Today. 13(2):12, 17- 18. Velovitch, J. J. 1983. Studies on postemergence grass herbicides f0r soybeans and uptake, translocation and metabolism of fluazifop-butyl in several plants. PhJL Dissertation. Univ. of Illinois at Urbana-Champaign. 115 pp. Nest, L. 0., J. H. Dawson, and A. P. Appleby. 1980. Factors influencing barnyardgrass (Echinochloa crus-galli) control with diclofop. Heed Sci. 28:366-371. CHAPTER 3 THE INFLUENCE OF TEMPERATURE, RAINFALL, AND TIME OF DAY ON THE EFFICACY 0F FLUAZIFOP-BUTYL ABSTRACT Fluazifop-butyl ((1)-butyl 2-[4-([S-trifluoromethyl)-2-pyridinyl] oxy) phenoxy] propanoate) toxicity to green foxtail (Setaria viridis) U”) Beauv.) but not Japanese millet (Echinochloa crusgalli var. frumentacea (Roxb.)), was significantly reduced as temperatures increased from l8»to 30 C. Temperature differences for green foxtail were not overcome by increasing herbicide rates up to 0.28 kg/ha. Herbicidal activity on both species was differentially influenced by applications made at 8 amn, 3 pm», and 10 pm», but no consistent pattern was observed. lkiparticular environmental factor could be associated with diurnal variation. Simulated rainfall within two hours of herbicide application reduced control of both species atllO7 kg/ha, but increasing the fluazifop-butyl rate to 0.14 kg/ha shortened the necessary rain-free interval to as low as 30 minutes. 106 1 INTRODUCTION Recent development of postemergence grass herbicides has provided a unique and flexible strategy for control of annual and perennial grass species. Toxicity of these graminicides is influenced by a number of environmental factors, as well as plant moropholigical characteristics (5). An understanding of these factors is necessary for optimal usage of these compounds. Air temperature differences may affect absorption, translocation, and ultimately herbicidal activity of foliar-applied graminicides (3, l7). Kel ls et. al. (8) reported greater quackgrass (Agropyron rep_ens (L.) Beauv.) control with fluazifop-butyl at 30 than at 20 C. From radiolabel studies with 14C-fluazifop-butyl, differences in herbicide absorption, and more extensive distribution of chemical throughout plants exposed to 30 C, were suggested as contributing to temperature differences. However, Hartzler and Foy (7) could not find a difference in the overall control of large crabgrass (Digitaria sanguinalis (LJ Scop.) by sethoxydim (2-[1-(ethoxyimino) butyll-S-[Z-(ethythio) propyl] -3-hydroxy-2-cyclohexen-l-one) or CGA-82725 (2-propynyl 2-[4- ([3,5-dichloro-2-pyridiny1] oxy) phenoxy] propanoate) when treated at various temperatures. They did report more rapid initial development of injury symptoms on plants maintained at 32 than at 16 C. Chow (2) reported wild oat (Avena fatua LJ control with diclofop-methyl (methyl 107 108 2-[4-(2,4-dichlorophenoxyd phenoxy] propanoate) decreased with increasing temperatures from 12 to 28 C. Differences in the diurnal response to postemergence graminicides has been demonstrated for selected annual grasses (l, 4, 12). Ennis and Ashley (4) found that sethoxydim and CGA-82725 provided better control of large crabgrass when applications were made in the morning and evening, compared to mid-day; Conditions of specific environmental factors such as air temperature, relative humidity, , and soil temperature at the time of herbicide application, were suggested as contributing to diurnal differences. Studies with simulated rainfall have demonstrated the ability of the graminicides to maintain their activity with rainfal'l applied as soon as 0.5 to 3 h after herbicide application (6, 9, l3, 14, 16). Rhodes and Coble (15) reported simulated rainfall of 1.3 cm to broadleaf signalgrass (Brachiaria platyphylla (Griseb.) Nash), could not reduce grass control if delayed more than 15 nfinutes after sethoxydim application. The objectives of this research were to determine the influence of temperature, time of day of application, and simulated rainfall, on the efficacy of fluazifop-butyl for two annual grasses. MATERIALS AND METHODS General greenhouse procedures. Green foxtail and japanese millet seedlings were grown in the greenhouse in 975 ml (12 cm diameter) plastic pots. These species were chosen based on previous research, which demonstrated them to be relatively tolerant and susceptible, to 109 fluazifop-butyl respectively. Soil media consisted of a 3:1 Spinks loamy sand to peat-perlite mix, with a combined pH of 6.2 to 6.4. Approximately 50 m1 of a soluble:fertilizer (Peters 20-20-20) at a concentration of 1 g/l was applied to all pots twice weekly. Natural light was supplemented with metal halide lighting at an average photosynthetic photon flux density (PPFD) of 290 umol°s']1n'2. A 14111 photoperiod was utilized for the timing study, with 16 h photoperiods for temperature and rainfall studies. Greenhouse air temperature averaged 25 C-day/ZO C-night, and relative humidity flucturated from 30 to 60%. One to three days prior to herbicide application, grasses were thinned to three to four uniform plants per pot. Foliar applications of formulated fluazifop-butyl (4 EC) were made with an air pressurized moving belt sprayer, equipped with an 8001 E even flat fan nozzle, and delivering 337 L/ha at a pressure of 235 kPa. All herbicide treatments included a petroleum based oil concentrate (80:20 petroleum oil to emulsifiers*) on a 0.7% v/v basis. Visual ratings of herbicidal activity, on a scale of 0 to 10 (0 = no effect, 10 = complete kill), were made 14 days after treatment for temperature study, and 16 days after treatment for timing and rainfall studies. l>lant tissue was also harvested, oven dried for two to three days at 55 C, and weighed. Effect 9: temperature. Nhen Japanese millet and green foxtail seedlings reached the early four- and six-leaf stage, respectively, plants were placed in growth chambers containing both fluorescent and incandescent lights. I’lants were exposed to an average PPFD of 215 *Torch crop oil concentrate, manufactured by Torch Chemicals, Division of Amoco Oil Company, Chicago, IL. 110 pmol°s"1'm'2 and a 16 h photoperiod. Air temperature was maintained at 18, 24, or 30 C, and relative humidity fluctuated for each temperature from 30 to 50, 35 to 60, and 40 to 70%, respectively; After 48 h, plants were treated with 0.035, 0.07, 0.14, and 0.28 kg/ha fluazifop- butyl and immediately returned to their respective growth chambers. Plants were surface irrigated within each growth chamber as necessary. Every third day, the pots were watered with 30 ml of the fertilizer solution. Seven days following treatment, all plants were removed from growth chambers and placed in the greenhouse. There were three replications within each temperature and data presented are the average of three experiments, in which chambers were assigned different temperatures within each experiment. Effect of time 91 application. Fluazifop-butyl applications of CLO35,(L07, and 0.14 kg/ha were made to Japanese millet seedlings which reached the four-leaf stage, and 0.07, 0.14, and 0.28 kg/ha to four-leaf green foxtail and both species at the six-leaf stage. All plants were surface irrigated 30 to 60 minutes prior to herbicide treatment at 8:00 a.m., 3:00 p.m., and 10:00 p.m. Average temperature and relative humidity in the greenhouse immediately'following treatment were 8:00 a.m., 18.9 C and 53.7%; 3:00 p.m., 24.1 C and 45.8%; 10:00 p.m., 21.4 C and 47.8%. Design of this 3 x 3 factorial experiment was a randomized complete block (RCB) with four replications. Each grass species and growth stage was a separate experiment. All studies were repeated three times except green foxtail at the four-leaf stage, which was repeated twice. Data presented are means of repeated experiments. 111 Effect of rainfall. Green foxtail and Japanese millet seedlings were treated with herbicide rates of 0.07 and 0.14 kg/ha at the five- and four-leaf stage, respectively. Simulated rainfall (approximately 1.7 cm) was applied with repeated applications through a two-nozzle boom, powered on a constant speed chain. Even if flat fan nozzles (8003 E), at a height of 20 to 25 cm above the plant canopy, delivered water at a pressure of 276 kPa. Rainfall was initiated O, 15, 30, 45, 60, 120, 240, and 4801ninutes after herbicide application. Fkn~each species, the two factor experiment was arranged in a RCB with four replications. Data presented are the means of two experiments. RESULTS AND DISCUSSION Effect of temperature. Significant differences in grass control due to temperature were found with green foxtail but not with Japanese millet (Figure l and 2, Table l). A trend comparison of temperature affects on green foxtail, revealed a significant linear increase in grass phytotoxicity with decreasing temperature (Table 1). For Japanesernillet, a large amount of unexplained variability resulted in a non-significant response to temperature, although grass control appeared consistently lower at 30 C (Figure 2). Results also indicated for both grasses a significant linear but curving response to increasing fluazifop-butyl rates (Figure l and 2, Table 1). Maximum injury on Japaneselnillet occurred at a lower herbicide rate (0.14 kg/ha) than for green foxtail (0.28 kg/ha). Table 1 indicates that, although temperature differences account for some treatment variability, herbicide rate was the predominant variable influencing Figure 1. 112 Response of green foxtail to fluazifop—butyl at 18, 24, and 30 C. 1 10 09 N] G (0 Mean Injury Rating «b 01 0) 113 0.035 0.07 0.14 Chemical Rate (Kg/Ha) 0.28 114 Figure 2. Response of Japanese millet to fluazifop-butyl at 18, 24, and 30 C. 0| 0’ N] Mean Injury Rating h 115 0.035 0.07 0.14 Chemical Rate (Kg/Ha) Ia 0.28 116 Table 1. Analysis of variance and trend comparisons for green foxtail and Japanese millet response to increasing fluazifop-butyl rates and air temperatures. Green Foxtail Japanese Millet Source df MS Fa MS F Total 107 Temperature 2 47.81 8.60** 17.58 0.73 Linear 1 93.39 16.8* 24.5 1.16 Quadratic 1 2.24 0.4 10.67 0.45 Error (a) 4 5.56 23.92 Chemical 3 290.09 344.48** 219.07 . 165.7** Linear 1 846.25 1007.4** 566.31 429.0** Quadratic l 21.33 25.4** 90.75 68.8** Cubic 1 2.67 3.18 0.15 0.11 Error (b) 90 0.84 1.32 aTabular F values for 2 and 4 df, p =0.05, 6.94; l and 4 df, p =0.05, 7.71, 3 and 90 df, p =0.01, 4.04; 1 and 90 df, p =0.01, 6.93. 117 grass control. A correlation of ratings and dry weight data was made, and revealed a close association. Averaging over replications within each experiment and temperature, the correlation coefficients (r) of green foxtail for 18, 24, and 30 C were -0.94 to -O.96, -0.97 to -0.98, and - 0.95 to -O.97, respectively. The coefficients for Japanese millet at the same temperatures were -0.86 to -0.98, -O.94 to -0.97, and -O.92 to -0.99, respectively. Results of this experiment agree with those of Chow (2) but conflict with other reports, which used fluazifop-butyl as well as other graminicides (8, 17). Greater phytoxicity at higher temperatures has been attributed to more absorption and translocation of the applied herbicides (8, 10, ll, 17). Autoradiographs by Kel ls et al. (8) and Hills (17) indicate~a greater distribution of graminicide at higher temperatures in quackgrass and bermudagrass (Cynodon dactylon (LJ Pers.L. One possible explanation for the reduced control of annual grasses at higher temperatures is an accumulation of flazifop-butyl in treated leaves and meristematic tissue at lower temperatures, with minimal translocation of the herbicide. In contrast, there may be dilution of the applied chemical through extensive translocation to plant parts at higher temperatures, subsequently reducing the concentration of actual herbicide at the site of action. This could have resulted in less initial injury'and greater regrowth oflalants exposed to higher temperatures. This could indicate that extensive distribution of graminicides is desirable and necessary for optimum control of perennial grasses, but may be detrimental to control of annual grasses. 118 {Effect g:_tjmg of application. Phytotoxicity to six-leaf Japanese millet and green foxtail at both stages was found to be significantly affected by the time of application (Figure 3, Table 2). However, there was no consistent pattern to indicate better control at one time of the day than another (Figure 3). In addition, the variability of treatment differences explained by time of application was very small compared to the influence of chemical rates (Table 2L. Therefore, although time of application could influence grass control, it is more likely that herbicide rate is the controlling factor. ‘There was a significant linear responseeof grass injury to increasing herbicide rates for each species and growth stage (Table 2). For four-leaf green foxtail, phytotoxicity also followed a curvilinear response with control being maximum at 0.14 kg/ha. Both green foxtail and Japanese millet were more tolerant to fluazifop-butyl at the six-leaf stage (Figure 3). This coincides with previous research, which indicated a wide range of annual grasses required higher chemical rates for consistent control, as they matured (data not presented) Results from dry weight data were generally'similar to visual ratings. The correlation coefficients (r) for repeated experiments of four- and six-leaf Japanese millet, and four- and six-leaf green foxtail were -0.94 to -0.96, -0.75 to -O.79, -O.90 to -0.96, and -O.87 'u3-4L89, respectively; Lower coefficients for larger grasses suggests biomass is often a poor indicator of the actual effect of fluazifop- butyl on each species. Figure 3. 119 Response of four- (A), and six-leaf (B) Japanese millet, and four-(C), and six-leaf (0) green foxtail to fluazifop- butyl, with morning (8:00 amt), mid-day (3:00 pmu) and evening (10:00 p.m.) applications. 120 A a 10 - 10{ 9- 9 - a - a - E 7" 7h 5 .. .. 5 - 5 - E (L50 0.05)I § 4 - 4 ' A 0 AM 2 (LSD 0.05) 9 3 PM 3 ~ 3 ' x 10 PM 2 _ A 8 A 2 .. o a ,_ x10PM 1- l ’J J J o 0.035' "17W 0.14 o 0.07 0.14 7:28 Chemical Rafe (Kg/Ha) Chemical Rate (Kg/Ha) c 0 10 ~ 10 . 0 - 9 - a» 8 - 3 "’ 7’ a .. .. E s - 5 - .5 (L50 0.05)I 5 4~ 4- g A 8 AM (Lso 0.05)] 3" e a PM 3' x 10 PM A 0 AM 2 - 2 - o 3 PM it 10 PM i i- 1 '- J J __.I J _l _J o 0.07 0.14 0.25 0 0.07 0.14 0.28 Chemical Rafe (Kg/Ha) Chemical Rate (Kg/Ha) 121 Table 2. Analysis of variance and trend comparison for green foxtail and Japanese millet response to increasing fluazifop-butyl rates. Green foxtail Japanese millet Growth Stage 4-leafa 6-1eaf 4-1eaf 6-1eaf Source df MS Fc MS F MS F MS F Total 107 Timeb 2 6.514 ** 16.396 ** 0.766 3.433 ** Chemical 2 139.149 ** 339.174 ** 477.919 ** 254.266 ** Linear 1 218.88 ** 678.347 ** 953.389 ** 506.681 ** Quadratic 1 59.418 ** 0 2,449 1.852 Time x chemical 4 5.597 ** 3.215 2.106 0.502 Error 72 1.105 1.690 2.706 0.521 aDegrees of freedom (df) for this experiment are 71 for total and 48 for QY‘Y‘OY‘. b CTabular F values for 2 and 72 df, p = 0.01, 4.91; 2 and 48 df, p = 0.01, Time - Time of application; 8:00 a.m., 3:00 p.m., and 10:00 p.m. 5.08; 4 and 72 df, p = 0.01, 3.59; 1 and 72 df, p = 0.01, 7.00. n 122 The apparent lack of a consistent optimal time for application is not in agreement with results found by previous researchers with other herbicides (1, 4, 12). Use of a different graminicide and grass species, varying environmental conditions, and conducting this experiment in the greenhouse, could explain these discrepancies. Ennis and Ashley (4) associated such environmental parameters as relative humidity, air and soil temperatures, and length of light after herbicide application, as possible factors affecting time of day differences. Nester and Harger (12), in a field trial, attributed time of day differences for diclofop-methyl control of itchgrass (Rottboellia exaltata L. F. ), primarily to soil moisture. Air temperature in this greenhouse experiment were consistently lower for morning (18.9 C), than afternoon (24.1 C) or evening (21.4 C) applications. Relative humidity was slightly higher for morning applications. Soil moisture was maintained at a suitable level for all plants. Differences in the time of application could not be associated with changes in an environmental factor that could occur in the field. From the results of this experiment, consistent control cfi’ an annual grass species is expected to depend on the stage of growth when an application is made, and the rate of herbicide used. Fluctuating environmental factors could affect control, but no generalization can be made to indicate an optimal time of day for herbicide application. Moi rainfall. Generally, simulated rainfall within two hours of fluazifop-butyl application reduced control of both Japanese rnillet and green foxtail (Figure 4). For both species, the rate of fluazifop-butyl influenced the time interval allowable between chemical application and rainfall. Rainfall on Japanese millet, treated with 123 Figure 4. Effect of simulated rainfall on the response of Japanese millet (A) and green foxtail (B) to fluazifop—butyl. 124 A ‘° ' 0.14 Kg/Ha A a .E g 0.07 Kg/Ha E‘ V 0 D E o A g (LSD 0.05) I I E l I J l 1 1F 0 15 30 45 50 120 246480 Rain-free interval (Minutes) 8 0.14 K [He 10 Q 4 A 9 3 o g’ 7 0.07 Kg/Ha 45 ‘6 m 6 >. ‘5 5 E 0 A 4 5 (LSD 0.05) I I 9 5 E 2 1 J l J J l J“ 0 15 30 45 50 120 240 430 Rain-free lntervai (Minutes) 125 0.07 kg/ha herbicide, was not effective in reducing grass control if delayed between 60 to 120 minutes. However, increasing the chemical rate to 0.14 kg/ha reduced the necessary rain-free interval to 30 to 60 minutes. For green foxtail treated with (L07 kg/ha, a rain-free interval of 60 to 1201ninutes*was also required, but this period was reduced to 30 to 45 minutes at 0.14 kg/ha. It is possible further increases in the herbicide rate could shorten the rain-free interval necessary for optimum control, but the cost of these herbicide rates could make this approach uneconomical. Adequate control of these and many other annual grasses at chemical rates comparable to those used in this experiment suggest moderate rainfall will not significantly affect grass control, if delayed up to two hours after chemical application. Note however, that experimental conditions were likely more ideal than those expected under field conditions. Environmental factors and growth stage, among other variables, could alter retention and absorption of the herbicide, thus affecting the rain-free interval necessary. The application of water through flat fan nozzles at relatively high pressure (276 kPa) might be more severe than expected from natural rainfall. A much larger distribution of small water droplets is expected to more effectively wash off herbicide than a natural rain. Dry weight data was similar to visual ratings. The correlation coefficients (r) of each experiment for Japanese millet and green foxtail was -0.98 and -0.93, and -O.84 and -0.90, respectively. The flexibility demonstrated by fluazifop-butyl to such factors as rainfall, time of application, and to a limited degree, temperature, allows effective control of green foxtail, Japaneselnillet and probably 126 numerous other annual grasses under various conditions. The herbicide rates and growth stages are suggested as predominant factors determining efficacy. LITERATURE CITED Ashley, R. A. 1982. Timing applications of diclofop for control of large crabgrass. Proc. Northeastern Need Sci. Soc. 36:199- 202. Chow, P. N. P. 1978. Selectivity and site of action in relation to field performance of diclofop. Need Sci. 26:352-358. Cranmer, J. R. and J. D. Nalewaja. 1981. Environment and BAS 9052 OH phytotoxicity. Proc. North Central Weed Control Conf. 36:26. Ennis, B. G. and R. A. Ashley. 1983. Effect of morning, mid-day and evening application on control of large crabgrass by several postemergence herbicides. Proc. Northeastern Need Sci. Soc. 37:155-160. Gilreath, J. P. 1983. Postemergence grass herbicides. Needs Today. l4(l):3-5. Harker, K. N. and R. N. Anderson. 1981. Volunteer corn and giant foxtail control in soybeans with BAS 9052 and R0-13-8895. Proc. North Central Weed Control Conf. 36:97-98. Hartzler, R. G. and C. L. Foy. 1983. Efficacy of three postemergence grass herbicides for soybeans. Heed Sci. 31:557- 561. 127 10. 11. 12. 13. 14. 15. 128 Kells, J. J., u. F. Meggitt, and D. Penner. 1984. Absorption, translocation, and activity of fluazifop-butyl as influenced by plant growth stage and environment. Need Sci. 32:143-149. Laube, B. C. and H. E. Arnold. 1982. Simulated rainfall treatment influence on postemergence grass control with CGA 82725, fluazifop-butyl, and Dowco 453. Proc. North Central Weed Control Conf. 37:73-74. McWhorter, C. G. 1979. The effect of surfactant and environment on the toxicity of metriflufen to soybeans (Glycine max) and johnsongrass (Sorghum halepense). Heed Sci. 27:675-679. McWhorter, C. G. 1981. Effect of temperature and relative humidity on translocation of 14C-metriflufen in johnsongrass (Sorghum halepense) and soybean (Glycine max). Heed Sci. 29:87-93. Nester, P. R. and T. R. Harger. 1982. Hour of diclofop application vs. itchgrass control. Proc. South. Need Sci. Soc. 35:34-35. Parsells, A” J., M. M. Fawzi, J. S. Claus, and J. C. Summers. 1983. DPX-Y6202 - a new postemergence grass herbicide for soybeans, cotton and other broadleaf crops. Proc. North Central Weed Control Conf. 38:14-15. Plowman, R. E., u. C. Stonebridge, and J. N. Hawtree. 1980. Fluazifop-butyl - - a new selective herbicide for the control of annual and perennial grass weeds. Proc. Brit. Weed Control Conf. 17:29-37. Rhodes,(L N” Jr” andlL D.Coble. 1983. Environmental factors affecting the performance of sethoxydim. Proc. South. Heed Sci. Soc. 36:154-155. 16. 17. 129 Nills, G. D. 1981. Effect of environment on the toxicity of BAS- 9052 [2-(N-ethoxybutyrimidoy1)-5-(2-ethy1thiopropyl)-3-hydroxy-2- cyclohexen-l-one] and KK-80 (ethyl-4-[4-[4-(trif1uoromethyl) phenoxy] phenoxy]-Z-pentenoate] to common bermudagrass (Cynodon dactylon L.). Abstr. Need Sci. Soc. Am. p. 9-10. Hills, G. D. 1984. Toxicity and translocation of sethoxydim in bermudagrass (Cynodon dactylon) as affected by environment. Need Sci. 32:20-24. CHAPTER 4 EFFECT OF CARRIER VOLUME AND ADJUVANT CONCENTRATION ON THE TOXICITY 0F FLUAZIFOP-BUTYL ABSTRACT Toxicity of fluazifop-butyl ((1)-butyl 2-[4-([5-(trif1uoromethyl)- 2- pyridinyl] oxy) phenoxy] propanoate) to large crabgrass (Digitaria sanguinalis (L.) Scop.) and stinkgrass (Erajrostis cilianensis (A11.) E. Mosher) in field studies, increased as carrier volumes decreased from 468 to 47 L/ha. Toxicity to large crabgrass in the greenhouse was significantly increased as carrier volumes decreased from 374 to 47 L/ha, and concentrations of a petroleum based crop oil concentrate increased from 0.625 to 5% v/v. Effects of carrier volumes and adjuvant concentrations were most pronounced with low herbicide rates that normal 1y provide marginal grass control. There was no significant interaction of adjuvant x spray volume, suggesting that each application factor inf1uenced grass control independently of the other. 130 INTRODUCTION Increasing utilization of postemergence herbicides has led to greater interest in spray application factors which could improve their effectiveness. The influence of application factors including spray volume and adjuvants have been assessed on 2,4-0 ([2,4-dichlorophenoxy] acetic acid), glyphosate (N-[phosphonomethyl] glycine), and gramoxone (1, l'-dimethy1-4,4'-bipyridinium ion), among others (3, 13, 18, 21, 22, 24). Recent research has shown that phytotoxicity of post-applied graminicides is influenced by carrier volume (5, 7, 11, 17) and adjuvants (2, 4, 5, 8, 10, 12, 16, 20, 23). Buhler and Burnside (5) reported fluazifop-butyl, haloxyfop-methyl (methyl 2-[4-([3-chloro-5-(trif1uoromethyl)-2-pyridinyl] oxy) phenoxy] propanoate), and sethoxydim (2-[1-(ethoxyimino) butyll-S-[Z-(ethylthio) propyl]-3-hydroxy-2-cyclohexen-l-one) toxicity to forage sorghum (Sorghum bicolor (L.) Moench 'Rox Orange') and yellow foxtail (Setaria lutescens (Weigel) Hubb.) was significantly greater at a carrier volume of 24 compared to 570 L/ha. Increasing chemical rates generally reduced the influence of carrier volume on herbicide toxicity. Charvat and Kinsella (7) noted more effective control of volunteer corn (£93 @215. L.) with sethoxydim as carrier volume was reduced, but differences diminished at higher herbicide rates. Hartzler and Foy (15) applied CGA-82725 (2-propyny1 2-[4-([3,5-dichloro-2-pyridinyl] oxy) phenoxy] 131 132 propanoate), RO-13-8895 (acetone 0-[D-(2-[p-(a,a,a-trif1uoro-p-toyl) oxy] phenoxy) propionyl] oxime), and sethoxydim to giant foxtail (Setaria faberi Herrm.), in carrier volumes of 93, 187, and 374 L/ha. No correlation between giant foxtail phytotoxicity and carrier volume could be found. Slack and Witt (26) treated annual grasses with fluazifop-butyl, haloxyfop-methyl, CGA-82725, and sethoxydim in 43, 118, and 236 L/ha using controlled droplet applicators, hollow cone, and flat fan nozzles, respectively. Results indicated no differences in grass control due to carrier volume or nozzle type. Buhler and Burnside (5) observed the addition of a petroleum based crop oil concentrate significantly increased fluazifop-butyl, haloxyfop-methyl, and sethoxydim toxicity to forage sorghum, compared to applications without an adjuvant. They also noted that increasing the concentration of adjuvant from 0.1 to 5% v/v general 1y improved sorghum control. Differences between adjuvant concentrations were more difficult to detect as herbicide rates increased. Hartzler and Fay (16) reported addition of adjuvants to sethoxydim was important in controlling 1arge crabgrass, but only at herbicide rates providing marginal control. However, adjuvants had little effect on the activity of CGA-82725 or R0-13-8895. Kel ls et a1. (19) found that increasing the concentration of either soybean oil concentrate or a petroleum based crop oil concentrate from 1 to 4% v/v, did not improve quackgrass (Agropyron repens (L.) Beauv.) control with sethoxydim. Objectives of this research were to determine the effect of carrier volume and concentration of a petroleum based crop oil concentrate on fluazifop-butyl activity on large crabgrass. MATERIALS AND METHODS Field Investigations General Procedures. Preliminary studies were conducted to determine herbicide rates and spray volumes necessary to observe differences in grass control. These studies were conducted at the Michigan State University Muck Research Station near Laingsburg, Michigan. Herbicide plots of 1.5 by 6.1 m were established on a Houghton muck soil (56% organic matter, pH 6JU. Formulated fluazifop- butyl (4 EC) was applied with a COZ-pressurized backpack sprayer. All applications were made with a 1.5 m boom, equipped with flat fan nozzles on 51 cm spacings. Natural populations of large crabgrass and stinkgrass were treated at 13 to 18 cm in height. Visual ratings (0 = no effect, 10 = complete kill) were made 12 days after treatment (DAT) in 1982, and 17 DAT in 1983. The factorial experiment was a randomized complete block (RCB) design with three replications in 1982, and four in 1983. 1982 Field Study. Fluazifop-butyl rates of 0.112, 0.28, and 0.56 kg/ha were applied in carrier volumes of 93JL 234, and 468 L/ha on July 29. A petroleum based crop oil concentrate (80:20 petroleum oil to emulsifiers*) was added to all treatments at the same rate per acre, *Torch crop oil concentrate, manufactured by Torch Chemicals, Division of Amoco Oil Company, Chicago, IL. 133 134 (1.1 L/ha), although adjuvant concentrations were 2.5, l, and 0.5% v/v for 93.5, 234, and 468 L/ha, respectively. Climatic conditions on this date included: air temperature 24 C, soil temperature 25 C, 63% relative humidity'(RH), northwest winds two to five miles per hour (mph), dry soil surface, and sunny skies. Nozzles 800067, 8003, and 8006 were used to deliver 9305, 234, and 468 L/ha carrier volumes, respectively. Broadleaf weeds were controlled with a broadcast application of 1.12 kg/ha nitrofen (2,4-dichloropheny1 p-nitrophenyl ether) on August 5. 1983 Field Study. Fluazifop-butyl rates of 0.035, 0.07, 0.14 and 0.28 kg/ha were applied in carrier volumes of 47, 93.5, 187, and 374 L/ha on July 8. Petroleum based crop oil concentrate was added to all treatments at the same rate per acre (1.1 L/ha), although concentrations were 5, 2.5, 1.25, and 0.625% v/v for carrier volumes of 47, 93.5, 187, and 374 L/ha, respectively. Climatic conditions on this date included: air temperature 28 C, soil temperature 32 C, 54% RH, southwest winds four to six mph, dry soil, and sunny skies. Nozzles 800067, 8002, and 8004 were used for low (47 L/ha), medium (93.5 L/ha), and higher (187 and 374 L/ha) carrier volumes, respectively. In this study, broadleaf weeds were managed by hand weeding. Greenhouse Investigations. General Procedures. Large crabgrass plants were grown in the greenhouse in 975 ml (12 cm diameter) plastic pots. Soil media consisted of a 3:1 Spinks loamy sand to peat-perlite mix, with a combined pH of 6.2 to 6.4. Approximately 50 m1 of a soluble fertilizer 135 (Peters 20-20-20) solution at a concentration of 1 g/l was applied to all pots twice weekly. Natural light was supplemented (16 h photoperiod) with metal halide lighting, at an average photosynthetic photon flux density (PPFD) of 290 umol°s‘1m"2. Greenhouse air temperature averaged 25 C-day/20 C-night, and relative humidity flucturated from 30 to 60%. One to three days prior to herbicide application, plants were thinned to three to four uniform grasses per pot. Large crabgrass was treated at the four-leaf stage, and 17 DAT visual ratings were recorded and plants harvested. After drying at 55 C, samples were weighed. Adjuvant Stugy. Foliar application of fluazifop-butyl at rates of 0.07, 0.14, and 0.28 kg/ha were made with an air pressurized moving belt sprayer. It was equipped with an 8001 Even flat fan nozzle, delivering 337 L/ha at a pressure of 235 kPa. A petroleum based crop oil concentrate (83:16 petroleum oil to emulsifiers*) was used at 0.625, 1.25, 2.5, and 5% v/v for each herbicide rate. This study was a two factor factorial placed in a RCB design with four replications. Data presented are the means of two experiments. Spray Volume and Adjuvant Study. A rate of 0.07 kg/ha fluazifop- butyl was applied with a 002-pres5urized backpack sprayer. This rate was expected to provide marginal control, based on previous research (data not presented). Carrier volumes of 47 and 93.5 L/ha were achieved with an 800067 nozzle while 187 and 374 L/ha were delivered using an 8004 nozzle tip. An adjuvant (Agicide Activator*) was used at *Agicide Activator, manufactured by Hopkins Agricultural Chemical Co” Madison, WI. 136 0.625, 1.25, 2.5, and 5% v/v for each spray volume. Design of this study was a RCB with four replications, and data presented are the means of two experiments. RESULTS AND DISCUSSION Field Investigations 1982 Field Study. In 1982, a spray volume of 93.5 L/ha resulted in greater control than 234 or 468 L/ha, but this was only evident at chemical rates of 0.112 kg/ha for both species, and 0.28 kg/ha for large crabgrass (Figure 1). As herbicide rates increased, the effect of spray volume diminished. All rates of fluazifop-butyl gave acceptable control of both species, defined as a rating of 7.5, and therefore no conclusion could be drawn to suggest a distinct advantage to implementing the use of lower carrier volumes. .Application of lower chemical rates could bring out differences in effectiveness at different spray volumes. It should be noted that for each spray volume, a different concentration of adjuvant was used. Therefore, differences attributed to spray volume, may in fact, have been influenced by the adjuvant concentrations. 1983 Field Study. In 1983, significant differences in grass control were again observed (Figure 2%. In general, an increase in carrier volume from 47 to 187 L/ha reduced control of both species. However, the carrier volume of 374 L/ha provided similar or superior control than 93.5 or 187 L/ha. It was observed that grass populations 137 Figure 1. Response of large crabgrass (A) and stinkgrass (B) to fluazifop—butyl at three carrier volumes, 1982. 10 N] O Q 01 Mean Injury Rating e or {A} 10 Mean. injury Rating Cl 138 // (LSD 0.0511 A 93.5 Llha 0 234 Llha X 468 Llha J 1 1 J J 0.112 0.224 0.336 0.448 0.56 Chemical Rate (Kg/Ha) (LSD 0.05) I A 93.5 Llha 0 234 Llha X 468 Llha J J J J ‘1 0.1 12 0.224 0.336 0.448 0.56 Chemical Rate (Kg/Ha) Figure 2. Response of large crabgrass (A) and stinkgrass (B) to fluazifop-butyl at four carrier volumes, 1983. NI 140 :1? I g 5 (LSD 0.05)I 15 § ‘ A 47 Llha 5 0 93.5 Llha 3 3 187 Llha z x 374 Llha 1 J J J J 0 0.035 0.07 0.14 0.28 Chemical Rate (Kg/Ha) 10 #3 9 8 g 7 E e E 5 f5 ‘ (LSD 0.05) I 0 2 3 A47 Llha o 93.5 Llha 2 3 187 Llha X 374 Llha 1 J J J] __l 0 0.035 0.07 0.14 0.28 Chemical Rate (Kg/Ha) 141 were dense in various areas throughout the plot. Possibly the volume of 374 L/ha provided more uniform plant coverage and herbicide penetration than lower volumes. As herbicide rates increased, the effect of spray volume was again diminished (Figure 2%. F0r both 1982 and 1983, stinkgrass was more susceptible than large crabgrass (Figure l and 2). As before, adjuvant concentrations varied with carrier volume, and observed spray volume differences could have been influenced by adjuvant concentration. Results from these field studies were used to construct greenhouse experiments designed to determine which application factor, spray volume and/or adjuvant concentration, influences grass phytotoxicity differences. Greenhouse Investigations Adjuvant Study. Large crabgrass control was affected by both adjuvant concentration and herbicide rate (Figure 3, Table l). A trend comparison of each variable revealed a significant linear response to increasing adjuvant concentrations, and a significant linear but curving response to increasing herbicide rates (Table 1). Differences were reduced as fluazifop-butyl rates increased (Figure 3). .Although increasing the adjuvant concentration inf1uenced phytotoxicity, this was primarily at herbicide rates which did not provide acceptable control (< 0.14 kg/ha). From Figure 3, no significant advantage is evident for increasing the adjuvant concentration above 1.25% v/v, at a chemical rate of 0.14 kg/ha. 'Table 1 indicates herbicide rate was the predominant variable influencing phytotoxicity. A1though adjuvant concentration can affect grass 142 Figure 3. Response of large crabgrass to fluazifop—butyl at fotn“ adjuvant concentrations (% v/v). ..A 0 Mean injury Rating 10 0) a on 01 s: 00 c0 d O 143 / I (LSD 0.05) I A 0.525% 0125% x 2.5% 3 5% 0 0.07 ' 0.14 0.23 Chemical Rate (Kg/Ha) 144 Table 1. Analysis of variance and trend comparisons for large crabgrass response to increasing fluazifop-butyl rates and adjuvant concentrations. Source df MS Fa Total 95 - - Adjuvant 3 6.95 42.82** Linear l 20.21 124.52** Quadratic l 0.59 3.63 Cubic 1 0.04 0.25 Chemical Rate 2 377.46 2325.69** Linear 1 708.89 4367.78** Quadratic l 46.02 283.55** Error 66 0.1623 - aTabular F values for 3 and 66 df, p = 0.01, 4.09; 2 and 66 df, p = 0.01, 4.94; 1 and 66 df, p = 0.01, 7.03. 145 control, it does not promote control for concentrations above 1.25% v/v, where herbicide rates provide commercially acceptable control. Results of dry weight data were similar to visual ratings. A correlation of these two responses for each experiment revealed a correlation coefficient (r) of -O.91 and -O.93, with line equations y = 0.571-0.053x and y = O.375-0.03x, respectively. Spray Volume and Adjuvant Study. Fluazifop-butyl toxicity to large crabgrass generally increased as spray volume was reduced from 374 to 47 L/ha, or adjuvant concentration increased from 0.625 to 5% v/v (Table 2L Visual ratings and tissue dry weight data were similar. From Table 2, visual ratings suggested a significant increase in grass phytotoxicity up to an adjuvant concentration of 2.5% v/v. Grass control was similar for spray volumes of 47 and 93.5 L/ha, both of which were more effective than 187 and 374 L/ha. A trend comparison for grass phytotoxicity to increasing adjuvant concentrations, revealed a significant linear response (Table 3). For increasing spray volumes, there was a linear response between 47 and 187 L/ha and an overall cubic response (Table 3). The carrier volume cfl’374 L/ha provided somewhat more effective grass control than 187 L/ha. There was no significant adjuvant by volume interaction, which suggests each variable affected grass control independently of the other. General Discussion. Results of volume differences agree with results of some researchers using other species or chemicals (5, 7, ll, 17), but not with others (14, 15, 26). One possible explanation for those studies which could not detect a response to spray volume, was that the herbicide rates used were too high. This is supported from 146 Table 2. Effect of spray volume and adjuvant concentration on the response of large crabgrass to fluazifop-butyl.a Adjuvant Concentration Spray Volume (% v/v) (L/ha) Visual Ratingb Dry weightC 0.625 6.08 0.44 1.25 6.91 0.41 2.5 7.95 0.28 5.0 8.06 0.24 46.8 8.41 0.20 93.5 8.64 0.21 187.0 5.66 0.50 374.0 6.30 0.46 LSD (0.05)d 1.10 0.14 aHerbicide rate was 0.07 kg/ha. b0 = no effect, 7.5 = acceptable control, 10 = complete kill. CWeight based on a g/plant basis. dEach visual rating and dry weight is based on the mean of 32 observations. 147 Table 3. Analysis of variance and trend comparison for large crabgrass response to increasing adjuvant concentrations and Spray volumes. Visual Ratinga Dry Heightb Source df MS FC Ms F Total 127 Adjuvant (ADJ) 3 28.22 5,77** 0.316 3.81* Linear 1 78.4_ 15.¢3** 0.878 10.58** Quadratic l 4.13 0.84 0.002 0.02 Cubic l 2.14 0.44 . 0.069 0.83 Volume (VOL) 3 71.67 14,55** 0.786 9,47** Linear 1 138.76 28.38** 1.757 2].]7** Quadratic l 1.32 0.27 0.015 0.18 Cubic 1 74.94 15.33** 0.588 7.08** ADJ x VOL 9 5.68 1.15 0.095 1.14 Error 90 4.89 0.083 a0 = no effect, 10 = complete kill. bHeight based on g/plant basis. CTabular F values for : 3 and 90 df, p = 0.01, 4.01; p = 0.05, 2.71; 1 and 90 df, p = 0.01, 6.93. 148 data of field experiments, indicating volume differences were more pronounced at lower chemical rates (Figure l and 2). The effectiveness of lower spray volumes could be due to droplet size, herbicide concentration, or retention characteristics. Buhler and Burnside (6) reported a larger percentage of small spray droplets from small orifice nozzles. This could result in greater surface contact, due to a more uniform spray distribution, and thus more herbicide absorption per unit time (5). The decrease in large crabgrass control with higher carrier volumes, in one study (Table 2) could be, in part, a result of droplet size differences. Smaller orifice nozzles (800067) were used for lower carrier volumes and larger orifice nozzles (8004) for higher volumes. Distinct differences in grass phytotoxicity occurred between 93.5 and 187 L/ha, but grass control was similar among 46.8 and 93.5 L/ha, and 187 and 374 L/ha. Decreasing spray volumes also increased herbicide concentration per spray droplet. Ambach and Ashford (1) observed an increase in barley (Hordeum vulgare (L.) 'Bonanza') phytoxicity when equal amounts of glyphosate were applied in droplets of increasing concentration. Similar results with fluazifop-butyl were reported by Buhler and Burnside (5). They suggested that with a higher herbicide concentration per droplet, more herbicide would be absorbed for each unit of spray solution which was retained on the leaf surface. Spray volume will affect the loss of herbicide due to runoff. Sandberg et a1. (24) suggested an increase in glyphosate toxicity as carrier volume decreased was the result of greater herbicide retention. However, no significant differences below 190 L/ha were observed. Buhler and Burnside (5) reported a marked decrease in grass control 149 when carrier volume was increased above 190 L/ha. Results from this study (Figure 2, Table 2) did not indicate a significant loss in grass control for spray volumes above 187 L/ha. Leaf surface characteristics of various species could alter the influence of herbicide runoff. For large crabgrass, the densely pubescent leaf surface could retain many different droplet sizes, thus reducing any loss in activity due to runoff. Observations indicating more effective grass control with an increase in adjuvant concentration are in agreement with Buhler and Burnside (5), as well as Hartzler and Foy (16), but not with Anderson (2) or Kel ls et a1. (19). Lack of a significant difference may have resulted from herbicide rates sufficient to provide effective control without an adjuvant or differences in species studied. Both Hartzler and Foy (16) and Buhler and Burnside (5) reported minimal effects of increasing adjuvant concentrations as herbicide rates increased. Susceptibility of a grass species to graminicides can also effect the influence of an adjuvant. For a number of annual species, Schreiber et al. (25) observed that only a species intermediately susceptible to diclofop was affected by the presence of a surfactant. The advantage of adjuvants has generally been attributed to increasing the leaf surface contact of the spray solution by reducing surface tension, and also increasing herbicide absorption. An increasing but leveling off of grass phytotoxicity with incremental changes in adjuvant concentration, could suggest a threshold level needed for maximum control (Figure 3), Table 2). The required level of adjuvant necessary for maximum control could vary with grass species and herbicide rate. Results from this experiment generally indicate a 150 concentration of 1.25 to 2.5% v/v will provide optimum control for recommended herbicide rates. The advantage of application factors such as spray volume and adjuvant concentration in optimizing control while minimizing herbicide rates, could dependlunnieach specific situation. Effects on large crabgrass may not be similar for other species. Species susceptibility, growth stage, and population density, should be considered before deciding upon a herbicide rate, spray volume, and adjuvant concentration. Although lower spray volumes and higher adjuvant concentrations can be beneficial under marginal control conditions, adequate herbicide rates.and unifornlplant coverage are prerequisites for consistent control. LITERATURE CITED Ambach, R. M. and R. Ashford. 1981. Effect of variations in drop makeup on the phytotoxicity of glyphosate. Need Sci. 29:221-224. Anderson, R. N. 1982. Comparisons of four herbicides applied postemergence for grass control. Proc. North Central Weed Control Conf. 37:80-82. Bayer, D. E. and H. R. Drever. 1965. The effect of surfactants on efficiency of foliar-applied diuron. Need Sci. 13:222-226. Bayer, G. H. and C. S. Russell. 1984. The influence of adjuvants on postemergence soybean herbicides. Proc. Northeastern Need Sci. Soc. 38:52. Buhler, 0.1L and O.(L Burnside. 1984. Effect of application factors on postemergence phytotoxicity of fluazifop-butyl, haloxyfop-methyl, and sethoxydim. Heed Sci. 32:574-583. Buhler, D. D. and O. C. Burnside. 1983. Effect of spray components on glyphosate toxicity to annual grasses. Need Sci. 31:124-130. Charvat, L. D. and J. Kinsella. 1983. Volunteer corn control in soybeans with sethoxydim. Proc. North Central Weed Control Conf. 38:21-22. Chernicky, J.l%, J. Gossett, and T. R.|Murphy. 1984. Factors influencing control of annual grasses with sethoxydhn or R0-13- 8895. Need Sci. 32:174-177. 151 10. 11. 12. 13. 14. 15. 16. 17. 18. 152 Colby, S. R., .L. T. Daniel, and [L A. Thomas. 1982. Postemergence control of perennial grasses.with sequential and single applications of PP009. Abstr. Weed Sci. Soc. Am. p. 16. Cranmer, J. R. and J. D. Nalewaja. 1981. Additives and BAS 9052 OH phytotoxicity. Proc. North Central Weed Control Conf. 36:96. Cranmer, J. R. and W. B. Duke. 1983. Control led droplet application (CDA) of fluazifop and sethoxydim for annual and perennial weed control. Abstr. Weed Sci. Soc. Am. p. 23-24. Ennis, B. G. and R. A. Ashley. 1984. Crop oil as additive for crabgrass control by several postemergence herbicides. Proc. Northeastern Weed Sci. Soc. 38:327-331. Ennis, W. B., Jr. and R. E. Williams. 1983. Influence of droplet size on effectiveness of low-volume herbicidal sprays. Weeds 11:67-72. Froseth, R. E. and W. E. Arnold. 1983. Effect of carrier volume on toxicity of several postemergence herbicides. Proc. North Central Weed Control Conf. 38:133. Hartzler, R. G. and C. L. Foy. 1982. Factors affecting performance of postemergence grass herbicides. Proc. South. Weed Sci. Soc. 35:96-97. Hartzler, R. G. and 0.1" Foy. 1983. Efficacy of three post- emergence grass herbicides for soybeans. Weed Sci. 31:557-561. Johnson, G. B. and F. J. Webb. 1983. Spray pressure, volume and tip study. Proc. Northeastern Weed Sci. Soc. 37:51-52. Jordan, T. N. 1981. Effects of diluent volumes and surfactant on the phytotoxicity of glyphosate to bermudagrass (Cynodon dactylon). Weed Sci. 29:79-83. 19. 20. 21. 22. 23. 24. 25. 26. 153 Kells, J. J., W. F. Meggitt, V. M. Sorenson, and J. L. Wilhm. 1983. Soybean oil as a spray adjuvant for foliar application with conventional and reduced volume systems. Proc. North Central Weed Control Conf. 38:28-29. Lunsford, J. 1983. Effect of herbicide rate, additives, growth stage, and competitive crop on the control of Texas panicum with fluazifop-butyl. Proc. South. Weed Sci. Soc. 36:149. McKinlay, K. 5., R. A. Ashford, and R. J. Ford. 1974. Effects of droplet size, spray volume, and dosage on paraquat toxicity. Weed Sci. 22:31-34. McWhorter, C. G. and T. N. Jordan. 1976. Effects of adjuvants and environment on the toxicity of dalapon to johnsongrass. Weed Sci. 24:257-260. O'Sullivan, P. A., H. A. Friesen, and W. H. VandenBorn. 1977. Influence of herbicides for broad-leaved weeds and ajduvants with diclofop-methyl on wild oat control. Can. J. Plant Sci. 57:117- 125. Sandberg, C. G., W. F. Meggitt, and D. Penner. 1978. Effect of diluent volume and calcium on glyphosate phytotoxicity. Weed Sci. 26:476-479. Schreiber, M. M., G. F. Warren, and P. L. Orwick. 1979. Effects of wetting agent, stage of growth, and species on the selectivity of diclofop. Weed Sci. 27:679-683. Slack, C. H., and W. W. Witt. 1983. Herbicide applications with CDA. Abstr. Weed Sci. Soc. Am. p. 54. IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII 11111111111111111111111111111111 1293