Donnie K. Miller

A proposal to standardize soil/solution herbicide distribution coefficients

Abstract Herbicide soil/solution distribution coefficients (Kd) are used in mathematical models to predict the movement of herbicides in soil and groundwater. Herbicides bind to various soil constituents to differing degrees. The universal soil colloid that binds most herbicides is organic matter (OM), however clay minerals (CM) and metallic hydrous oxides are more retentive for cationic, phosphoric, and arsenic acid compounds. Weakly basic herbicides bind to both organic and inorganic soil colloids. The soil organic carbon (OC) affinity coefficient (Koc) has become a common parameter for comparing herbicide binding in soil; however, because OM and OC determinations vary greatly between methods and laboratories, Koc values may vary greatly. This proposal discusses this issue and offers suggestions for obtaining the most accurate Kd, Freundlich constant (Kf), and Koc values for herbicides listed in the WSSA Herbicide Handbook and Supplement. Nomenclature: Readers are referred to the WSSA Herbicide Handbook and Supplement for the chemical names of the herbicides.

Glyphosate-Insecticide Combination Effects on Weed and Insect Control in Cotton'

Field studies were conducted to evaluate weed control with combinations of glyphosate at 750 g ae/ha and the insecticides acephate (370 g ai/ha), dicrotophos (370 g ai/ha), dimethoate (220 g ai/ha), fipronil (56 g ai/ha), imidacloprid (53 g ai/ha), lambda-cyhalothrin (37 g ai/ha), oxamyl (280 g ai/ha), or endosulfan (420 g ai/ha) and insect control with coapplication of the herbicide with insecticides acephate, dicrotophos, dimethoate, and imidacloprid. Applying lambda-cyhalothrin or fipronil with glyphosate reduced control of hemp sesbania by 19 and 9 percentage points, respectively, compared with glyphosate alone. Acephate, dicrotophos, dimethoate, imidacloprid, lambda-cyhalothrin, oxamyl, and endosulfan did not affect hemp sesbania, pitted morningglory, prickly sida, and redweed control by glyphosate. Lambda-cyhalothrin and fipronil did not affect glyphosate control of weeds other than hemp sesbania. Addition of glyphosate to dicrotophos improved cotton aphid control 4 d after treatment compared with dicrotophos alone. Thrips control was improved with addition of glyphosate to imidacloprid. Insect control was not reduced by glyphosate regardless of insecticide. Nomenclature: Acephate, O, S-dimethyl acetylphosphoramidothioate; dicrotophos, 3-dimethoxyphosphinoyloxy-N,N-dimethylisocrotonamide; dimethoate, O,O-dimethyl-S-methylcarbamoylmethyl phosphorodithioate; endosulfan, (1,4,5,6,7,7-hexachloro-8,9,10-trinorborn-5-en-2,3-ylenebismethylene)sulfite; fipronil, 5-amino-1-(2,6-dichloror-α,α,α-triflouro-p-tolyl)-4-trifluoromethylsulfinylpyrazole-3-carbonitrile; glyphosate; imidacloprid, (EZ)-1-(6-chloro-3-pyridylmethyl)-N-nitroimidazolidin-2-ylideneamine; lambda-cyhalothrin, reaction product comprising equal quantities of (S-α-cyano-3-phenoxybenzyl (Z)-(1R,3R)-3-(2-chloro-3,3,3-trifluoropropenyl)-2,2-dimethylcyclopropanecarboxylate and (R)-α-cyano-3-phenoxybenzyl (Z)-(1S,3S)-3-(2-chloro-3,3,3-trifluoropropenyl)-2,2-dimethylcyclopropanecarboxylate or of (S)-α-cyano-3-phenoxybenzyl (Z)-(1R)-cis-3-(2-chloro-3,3,3-trifluoropropenyl)-2,2-dimethylcyclopropanecarboxylate and (R)-α-cyano-3-phenoxybenzyl (Z)-(1S)-cis-3-(2-chloro-3,3,3-trifluoropropenyl)-2,2-dimethylcyclopropanecarboxylate; oxamyl, (EZ)-N,N-dimethyl-2-methylcarbamoyloxyimino-2-(methylthio)acetamide; hemp sesbania, Sesbania exaltata (Raf.) Rydb. ex A. W. Hill #3 SEBEX; AESVI; pitted morningglory, Ipomoea lacunosa L. # IPOLA; prickly sida, Sida spinosa L. # SIDSP; redweed, Melochoia corchorifolia L. # MEOCO; cotton, Gossypium hirsutum L; cotton aphids, Aphis gossypii Glover; thrips, Frankliniella spp. Additional index words: Aphids, herbicide–insecticide combinations, pesticide compatibility, thrips. Abbreviations: DAT, days after treatment; POST, postemergence.

Interference between Rottboellia cochinchinensis and Zea mays

Abstract Field studies conducted over 2 yr in Louisiana determined critical periods of Rottboellia cochinchinensis interference in Zea mays. In a duration of interference study, R. cochinchinensis was allowed to compete with Z. mays for 0 (weed-free, season-long), 2, 4, 6, 8, 10, 12, or 14 (weedy, season-long) wk, after which plots were maintained weed-free for the rest of the growing season. Rottboellia cochinchinensis biomass at time of initial removal increased linearly as weeks of interference increased. For 2 wk of interference, R. cochinchinensis biomass was greater in 1993 than 1994, but for 4 wk or more of interference, biomass was greater the second year indicating environmental conditions were more conducive to R. cochinchinensis growth in 1994. Season-long R. cochinchinensis interference reduced Z. mays height by 18% compared with the weed-free check. For both years, R. cochinchinensis reduced yields 125 kg ha−1 for each week of interference. In weed-free maintenance studies, 0, 2, 4, 6, 8, 10, 12, or 14 (weed-free, season-long) wk of weed-free conditions were provided, after which R. cochinchinensis was allowed to repopulate. Zea mays yield was equivalent for the weed-free control and plots maintained free of R. cochinchinensis for 2 wk or more. In the interference studies, season-long R. cochinchinensis interference reduced Z. mays yield at least 33% compared with the season-long weed-free check. Nomenclature: Rottboellia cochinchinensis (Lour.) W. Clayton ROOEX, itchgrass; Zea mays L. DeKalb 689, corn.

MSMA Antagonizes Glyphosate and Glufosinate Efficacy on Broadleaf and Grass Weeds

Field and greenhouse studies were conducted to investigate the compatibility of MSMA in a tank mixture with glyphosate or glufosinate for broadleaf and grass weed control. Glyphosate, glufosinate, and MSMA were evaluated at 0.5×, 1×, and 2× rates, with 1× rates of 0.84 kg ae/ha, 0.5 kg ai/ha, and 2.2 kg ai/ha, respectively. Glyphosate and glufosinate provided similar levels of control for most weed species and were often more efficacious than MSMA alone. Glyphosate controlled Palmer amaranth better than glufosinate. Glufosinate controlled hemp sesbania, pitted morningglory, and ivyleaf morningglory better than glyphosate at one location. Weed control was not improved with the addition of MSMA to glyphosate or glufosinate when compared with either herbicide alone. MSMA antagonized glyphosate efficacy on barnyardgrass, browntop millet, hemp sesbania, Palmer amaranth, and redroot pigweed. MSMA antagonized glufosinate efficacy on browntop millet, hemp sesbania, ivyleaf morningglory, johnsongrass, Palmer amaranth, pitted morningglory, prickly sida, redroot pigweed, and velvetleaf. Antagonism of glyphosate or glufosinate by MSMA was often overcome by applying the 2× rate of either herbicide alone. MSMA is not a compatible tank-mixture partner with glyphosate or glufosinate for weed control in cotton. Nomenclature: Glyphosate, glufosinate, MSMA, common barnyardgrass, Echinochloa crus-galli (L.) P. Beauv. ECHCG, browntop millet, Brachiaria ramosa (L.) Stapf PANRA, hemp sesbania, Sesbania exaltata (Raf.) Rydb. ex A. W. Hill SEBEX, ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. IPOHE, johnsongrass, Sorghum halepense (L.) Pers. SORHA, palmer amaranth, Amaranthus palmeri S. Wats. AMAPA, pitted morningglory, Ipomoea lacunosa L. IPOLA, prickly sida, Sida spinosa L. SIDSP, redroot pigweed, Amaranthus retroflexus L. AMARE, velvetleaf, Abutilon theophrasti Medik. ABUTH, cotton, Gossypium hirsutum L

Response of nonglyphosate-resistant cotton to reduced rates of glyphosate

Abstract Field research was conducted in 1999 and 2000 to determine the effect of reduced glyphosate rates on growth and yield of nonglyphosate-resistant cotton. Rates of 9, 18, 35, 70, 140, and 280 g ha−1, representing 0.008, 0.016, 0.031 0.063, 0.125, and 0.25, respectively, of the maximum use rate per application (1,120 g ha−1), were applied to cotton at the two-, five-, or nine-node growth stage. On the basis of visual injury estimates, cotton was more tolerant to glyphosate at the nine-node than at earlier growth stages. Plant dry weight was reduced with 70 g ha−1 of glyphosate or higher, when applied at the two- and five-node growth stages in two of three experiments. Dry weight was not affected by glyphosate at the nine-node stage. Plant height also was unaffected by glyphosate rates below 70 g ha−1, but height reduction was noted for all growth stages by experiment combinations, with the exception of the nine-node application for both experiments in 2000, with herbicide rates of 70 g ha−1 or higher. Cotton maturity delay, as noted by an increase in node above white flower number, was observed only at the highest glyphosate rate applied to two- and five-node cotton in one of three experiments. Percent open boll data analysis indicated a decreased opportunity of observing an open boll with increasing glyphosate rate, and this effect was greater at the five-node compared with the two- and nine-node stages in two of three experiments. Seedcotton yield after all glyphosate applications was equivalent to that for the nontreated control. Nomenclature: Glyphosate; cotton, Gossypium hirsutum L. ‘Stoneville 474’, ‘DP33B’.

Herbicides As Harvest Aids

Abstract Herbicides used as harvest aids are applied at crop maturity to desiccate weed and crop foliage. Weeds present in the harvested crop can increase moisture content and foreign material, reducing grade and market price. Weeds can also delay the harvest operation and reduce harvest efficiency. Glyphosate can be used to desiccate weeds in glyphosate-resistant crops without concern for crop injury. Carfentrazone and pyraflufen-ethyl used as harvest aids can be effective in desiccating broadleaf weeds in corn and soybean. Paraquat, although effective on grass and broadleaf weeds when applied late season, can cause significant crop injury if applied too early. With expanded production of early maturing soybean cultivars in the mid-South (Arkansas, Louisiana, Mississippi, Missouri bootheel, and west Tennessee), presence of green stems, green pods, or green leaf retention, or combinations of these at harvest has increased. Interest in harvest aids has shifted to use as a crop desiccant. Paraquat also is an effective soybean desiccant, but application timing differs for indeterminate and determinate cultivars. Paraquat applied after soybean seed reached physiological maturity reduced number of green stems, pods, and retained green leaves present, allowing harvest to proceed 1 to 2 wk earlier than nontreated soybean. Seed moisture, foreign material, and seed damage also were reduced when paraquat was applied. Nomenclature: Corn, Zea mays L.; soybean, Glycine max (L.) Merr.

Influence of Adjuvants on Itchgrass (Rottboellia cochinchinensis) Control in Corn (Zea mays) with Nicosulfuron and Primisulfuron1

Abstract: In field experiments, nicosulfuron at 35 g ai/ha controlled itchgrass in corn 28 d after treatment better than primisulfuron at 39 g ai/ha (80 vs. 44%). Control with both herbicides was greater when applied to six-leaf itchgrass than to 10-leaf and with the addition of nonionic surfactant than with an organosilicone surfactant and methylated seed oil blend. Weed control for nicosulfuron plus nonionic surfactant resulted in corn yield approximately 1.5 times that of primisulfuron plus nonionic surfactant and 1.6 times that of nicosulfuron plus an organosilicone surfactant and methylated seed oil blend. When primisulfuron was applied with organosilicone surfactant and methylated seed oil rather than nonionic surfactant, corn yield was reduced by 25%. For nicosulfuron with nonionic surfactant, corn yield averaged approximately twice that of the nontreated check. In other field experiments, itchgrass control 28 d after treatment with nicosulfuron was enhanced with addition of an organosilicone and nonionic surfactant blend or methylated seed oil (83 and 78%, respectively) compared with nonionic surfactant (69%). Nicosulfuron was less effective when applied with crop oil concentrate or organosilicone surfactants compared with nonionic surfactant. Nomenclature: Nicosulfuron, 2-[[[[(4,6-dimethoxy-2-pyrimidinyl)amino]carbonyl]amino]sulfonyl]-N,N-dimethyl-3-pyridinecarboxamide; primisulfuron, 2-[[[[[4,6-bis(difluoromethoxy)-2-pyrimidinyl]amino]carbonyl]amino]sulfonyl]benzoic acid; itchgrass, Rottboellia cochinchinensis (Lour.) W. Clayton #3 ROOEX; corn, Zea mays L. ‘DeKalb 689’. Additional index words: Crop oil concentrate, methylated seed oil, nonionic surfactant, organosilicone surfactant, ROOEX. Abbreviations: DAT, days after treatment; POST, postemergence; PRE, preemergence.

Glyphosate Efficacy on Selected Weed Species Is Unaffected by Chemical Coapplication1

A study was conducted in 2004 to determine the effect of coapplication of the insecticides acephate, acetamiprid, bifenthrin, cyfluthrin, cypermethrin, dicrotophos, dimethoate, emanectin benzoate, imidacloprid, indoxacarb, lambda-cyhalothrin, methoxyfenozide, spinosad, thiamethoxam, and zeta-cypermethrin; the plant growth-regulator mepiquat pentaborate; a foliar sodium calcium borate micronutrient solution; and a foliar nitrogen fertilizer solution with glyphosate on the efficacy of weeds that commonly infest cotton. Barnyardgrass, hemp sesbania, johnsongrass, pitted morningglory, and sicklepod were grown in outdoor containers and treated with glyphosate at 1,120 g ai/ha alone or in coapplication at the three-to four- or seven-to eight-leaf growth stage. Glyphosate efficacy, based on visual control ratings at 7, 14, and 28 d after treatment (DAT) and fresh weight reduction of weed biomass at 28 DAT, was unaffected by chemical coapplication or application timing. Averaged across application timing and visual rating interval, glyphosate alone controlled barnyardgrass 97%, hemp sesbania 68%, johnsongrass 98%, pitted morningglory 68%, and sicklepod 89%. These results indicate that glyphosate coapplications evaluated offer producers the ability to combine pest and crop management strategies and reduce application costs without sacrificing control of weeds evaluated. Nomenclature: Acephate; acetamiprid; bifenthrin; cyfluthrin; cypermethrin; dicrotophos; dimethoate; emanectin benzoate; glyphosate; imidacloprid; indoxacarb; lambda-cyhalothrin; mepiquat pentaborate; methoxyfenozide; nitrogen fertilizer solution, (18.8% urea nitrogen and 6.2% water-soluble nitrogen); sodium calcium borate 10%; spinosad; thiamethoxam; zeta-cypermethrin; barnyardgrass, Echinochloa crus-galli (L.) P. Beauv. #3 ECHCG; hemp sesbania, Sesbania exaltata (Raf.) Rydb. ex A. W. Hill # SEBEX; johnsongrass, Sorghum halepense (L.) Pers. # SORHA; pitted morningglory, Ipomoea lacunosa L. # IPOLA; sicklepod, Senna obtusifolia (L.) Irwin and Barneby # CASOB. Additional index words: Herbicide–insecticide combinations, pesticide compatibility. Abbreviations: DAT, days after treatment; RCB, randomized complete block.

Preemergence herbicide and glyphosate effects on seedling diseases in glyphosate-resistant cotton

Field experiments were conducted to evaluate the influence of preemergence (PRE) herbicides metolachlor at 1,700 g ai/ha, pyrithiobac at 70 g ai/ha, or pendimethalin at 840 g ai/ha applied alone or with fluometuron at 1,300 g ai/ha and glyphosate postemergence (POST) at 840 g ai/ha on seedling diseases in glyphosate-resistant cotton. Hypocotyl disease severity both years averaged across PRE herbicide treatments was greater after glyphosate application to four-leaf cotton than cotyledon cotton. The PRE herbicide treatments, particularly those including fluometuron, increased root and hypocotyl disease ratings compared with a nontreated control, and a sequential application of glyphosate did not further increase disease severity. Greenhouse experiments using soil infested with Rhizoctonia solani confirmed findings from the field study showing that PRE herbicides can predispose cotton to greater seedling disease injury with no increased seedling disease severity associated with application of glyphosate. In the field study, glyphosate applied at cotyledon or four-leaf growth stages decreased disease severity on cotton hypocotyls both years. This inhibitory effect of glyphosate was less evident in the greenhouse study and may have been related to species of fungi present, infestation level, and differences in environmental conditions when compared with the field. Nomenclature: Fluometuron; glyphosate; metolachlor; pendimethalin; pyrithiobac; Rhizoctonia solani; cotton, Gossypium hirsutum L. Additional index words: Gossypium hirsutum L., ‘D&PL 5690 RR’, ‘D&PL 5415 RR’, ‘D&PL 436 RR’, herbicide–pathogen interactions, seedling diseases. Abbreviations: EPSP, enolpyruvylshikimate phosphate; fb, followed by; PDA, potato dextrose agar; PRE, preemergence; POST, postemergence.

Efficacy of Residual And Non-Residual Herbicides Used in Cotton Production Systems When Applied with Glyphosate, Glufosinate, or Msma

Field experiments were conducted to evaluate weed control provided by glyphosate, glufosinate, and MSMA applied alone or in mixture with residual and nonresidual last application (LAYBY) herbicides. Herbicide treatments included glyphosate early postemergence (EPOST) alone or followed by glyphosate, glufosinate, or MSMA late-postemergence (LPOST) alone or tank-mixed with one of the following LAYBY herbicides: carfentrazone-ethyl at 0.3 kg ai/ha, diuron at 1.12 kg ai/ha, flumioxazin at 0.07 kg ai/ha, fluometuron at 1.12 kg ai/ha, lactofen at 0.84 kg ai/ha, linuron at 0.56 kg ai/ha, oxyfluorfen at 1.12 kg ai/ha, prometryn at 1.12 kg ai/ha, or prometryn + trifloxysulfuron at 1.12 kg ai/ha + 10 g ai/ha. Residual herbicides were also applied alone LPOST. Weeds evaluated included barnyardgrass, broadleaf signalgrass, coffee senna, entireleaf morningglory, hemp sesbania, ivyleaf morningglory, johnsongrass, large crabgrass, Palmer amaranth, pitted morningglory, prickly sida, redroot pigweed, sicklepod, smooth pigweed, spiny amaranth, and velvetleaf. Treatments containing MSMA provided lower average weed control compared to those containing glyphosate or glufosinate, and residual herbicides applied alone provided inadequate weed control compared to mixtures containing a nonresidual herbicide. Across 315 of 567 comparisons (55%), when a LAYBY herbicide was added, weed control increased. The most difficult to control weed species at all locations was pitted morningglory. Barnyardgrass and hemp sesbania at the Mississippi location and hemp sesbania at the Louisiana location were collectively difficult to control across all treatments as well. Nomenclature: carfentrazone-ethyl; diuron; flumioxazin; fluometuron; glufosinate; glyphosate; lactofen; linuron; MSMA; oxyfluorfen; prometryn; trifloxysulfuron; barnyardgrass, Echinochloa crus-galli (L.) Beauv. ECHCG; broadleaf signalgrass, Brachiaria platyphylla (Griseb.) Nash BRAPP; coffee senna, Cassia occidentalis L. CASOB; entireleaf morningglory, Ipomoea hederacea var. integruiscula Grey IPOHG; hemp sesbania, Sesbania exaltata (Raf.) Rydb.ex A. W. Hill SEBEX; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq IPOHE; johnsongrass, Sorghum halepense L. Pers. SORHA; large crabgrass, Digitaria sanguinalis (L.) Scop. DIGSA; Palmer amaranth, Amaranthus palmeri L. AMAPA; pitted morningglory, Ipomoea lacunosa L. IPOLA; prickly sida, Sida spinosa L. SIDSP; redroot pigweed, Amaranthus retroflexus L. AMARE; sicklepod, Senna obtusifolia (L.) Irwin & Barnaby CASOB; smooth pigweed, Amaranthus hybridus L. AMACH; spiny amaranth, Amaranthus spinosus L. AMASP; velvetleaf, Abutilon theophrasti Medik. ABUTH; cotton, Gossypium hirsutum L