Monosodium Salt Of Methylarsonic Acid Research Articles

Influence of Pyrithiobac Application Rate and Timing on Weed Control and Cotton Yield in Greece1

Field experiments were conducted at four locations (Larissa, Halkidona, Thessaloniki, and Halastra) in Greece to evaluate weed and cotton response to various pyrithiobac rates applied preplant incorporated (PPI), preemergence (PRE), or postemergence (POST). Pyrithiobac applied PPI or PRE at 0.068, 0.102, or 0.136 kg ai/ha controlled black nightshade, pigweeds, and common purslane at Larissa. However, pyrithiobac applied PRE at Thessaloniki and Halkidona was more effective against black nightshade and pigweeds than pyrithiobac applied PPI. Pyrithiobac applied PPI or PRE at 0.068 or 0.102 kg/ha did not control common lambsquarters at Thessaloniki. Weed control with trifluralin plus fluometuron applied PPI and alachlor plus fluometuron applied PRE at Larissa was slightly lower than that obtained with pyrithiobac. At Halkidona, trifluralin plus fluometuron applied PPI and alachlor plus fluometuron applied PRE provided weed control similar to that obtained with pyrithiobac. But at Thessaloniki, these treatments provided better weed control than pyrithiobac. Furthermore, pyrithiobac applied early postemergence (EPOST), midpostemergence, or in sequential systems controlled black nightshade and pigweeds, but it resulted in fair to good control of common purslane, velvetleaf, and common cocklebur. None of the POST treatments controlled common lambsquarters. Fluometuron EPOST controlled black nightshade, common lambsquarters, and common purslane ≥70, 86, and 67%, respectively. Fluometuron EPOST did not control pigweeds, velvetleaf, and common cocklebur. Cotton treated with pyrithiobac, regardless of method of application, yielded similar to the weed-free control. Cotton treated with pyrithiobac PPI at the highest rate (0.136 kg/ ha) yielded less at Halkidona, although adverse effects after its application were not visually apparent. Yield of cotton treated with herbicides was similar, with no difference among treatments.Nomenclature: Alachlor; fluometuron; pyrithiobac; trifluralin; black nightshade, Solanum nigrum L. #3 SOLNI; common cocklebur, Xanthium strumarium L. # XANST; common lambsquarters, Chenopodium album L. # CHEAL; common purslane, Portulaca oleracea L. # POROL; prostrate pigweed, Amaranthus blitoides S. Wats AMABL; redroot pigweed, Amaranthus retroflexus L. # AMARE; velvetleaf, Abutilon theophrasti Medicus # ABUTH; cotton, Gossypium hirsutum L. ‘Stoneville 474’, ‘Hazera Vered’, ‘Deltapine 20’, ‘Deltapine 50’, ‘Stoneville Bravo’.Additional index words: Application timing, cotton herbicide, crop injury, residual activity.Abbreviations: EPOST, early postemergence; MPOST, midpostemergence; MSMA, monosodium salt of methylarsonic acid; POST, postemergence; PPI, preplant incorporated; PRE, preemergence; WAP, weeks after planting; WAT, weeks after treatment.

Tolerance of Seedling Bermudagrass to Postemergence Herbicides

The introduction of improved seeded cultivars of bermudagrass [Cynodon dactylon (L.) Pers.] has generated significant interest from the turfgrass industry. An important component of successfully establishing these new cultivars will be to develop effective weed control strategies for the critical establishment period. A field study and a greenhouse study were conducted to evaluate the tolerance of several seeded bermudagrasses to commonly used postemergence herbicides at different periods of establishment. In a field study, ‘Princess’ bermudagrass was seeded at a rate of 48 kg ha−1 during the early summer of 2000 and 2001. Postemergence herbicides were applied at either 1, 2, or 4 wk after emergence (WAE). Herbicide treatments included MSMA (monosodium salt of methylarsonic acid) at 1.12 kg ha−1, metsulfuron (2[[[[(4‐methoxy‐6‐methyl‐1,3,5‐triazin‐2yl] amino] carboxyl] amino] sulfonyl]‐2‐benzoic acid) at 0.021 kg ha−1, diclofop ((±)‐2‐[4‐(2,4‐dichlorophenoxy) phenoxy]propanoic acid) at 1.12 kg ha−1, clopyralid (3,6 dichloro‐2‐pyridinecarboxylic acid) at 0.56 kg ha−1, dicamba (3,6‐dichloro‐2‐methoxybenzoic acid) at 0.56 kg ha−1, 2,4‐D amine D [(2,4‐ dichlorophenoxy) acetic acid at 0.56 kg ha−1, and quinclorac (3, 7‐dichloro‐8‐quinolinecarboxylic acid) at 0.842 kg ha−1 Visual injury ratings were recorded at 3, 5, 7, 15, and 30 d after treatment (DAT) and percent turfgrass cover was recorded at 30 and 60 DAT. In the greenhouse study, the same herbicides and treatments were used with the cultivars Princess, Yukon, NuMex Sahara, Jackpot, and Mirage. In both the field and greenhouse studies, there was no clear effect of application timing on the tolerance of seedling bermudagrass to herbicides. Diclofop and metsulfuron caused the highest levels of injury in both years of the field study and in the greenhouse study. The other herbicides tested caused less injury. The bermudagrass recovered from all herbicide injury by 30 d after treatment. The results from this study indicate that seedling bermudagrass is relatively tolerant of many commonly used postemergence herbicides as soon as 1 WAE. These results will be useful to turfgrass managers who are considering use of improved cultivars in various turf situations.

Weed Management in Cotton with CGA-362622, Fluometuron, and Pyrithiobac

An experiment was conducted at five locations in North Carolina during 2000 and 2001 to evaluate weed control, crop injury, and cotton yield. Weed management systems included different combinations of pyrithiobac preemergence (PRE), fluometuron PRE, CGA-362622 postemergence (POST), pyrithiobac POST, and monosodium salt of methylarsonic acid (MSMA) plus prometryn applied late POST-directed (LAYBY). At Goldsboro in 2000, cotton was injured 74 to 78% by CGA-362622 POST when evaluated 4 to 7 d after treatment (DAT). Injury at Clayton, Goldsboro, and Lewiston in 2001 and Rocky Mount in 2000 was less than 16% 4 to 7 DAT with the same treatment and was not apparent by 62 DAT. CGA-362622 controlled common lambsquarters, common ragweed, Palmer amaranth, sicklepod, smooth pigweed, andIpomoeaspecies including entireleaf, ivyleaf, and pitted morningglory, and the addition of pyrithiobac to the herbicide system, either PRE or POST, increased control ofAmaranthusspecies, jimsonweed, and prickly sida. CGA-362622 did not control jimsonweed or prickly sida. Fluometuron PRE, pyrithiobac PRE, and MSMA plus prometryn LAYBY were beneficial for increasing weed control and cotton lint yields. Prometryn plus MSMA LAYBY increased control of common ragweed, entireleaf morningglory, jimsonweed, pitted morningglory, and smooth pigweed and provided higher cotton yields than similar systems without a LAYBY. The greatest weed control and greatest cotton lint yields required complete weed management systems that included a combination of PRE, POST, and LAYBY treatments.

Weed Efficacy Evaluations for Bromoxynil, Glufosinate, Glyphosate, Pyrithiobac, and Sulfosate

Thirteen field trials were conducted in 1999 and 2000 to evaluate postemergence (POST) weed control with single applications of bromoxynil at 420 or 560 g ai/ha, glufosinate at 291 or 409 g ai/ha, glyphosate at 1,120 g ai/ha, pyrithiobac at 36 or 72 g ai/ha, or sulfosate at 1,120 g ai/ha. Additional treatments evaluated included two applications with glufosinate at both rates in all possible combinations, two applications of glyphosate, and two applications of sulfosate. Weeds were 2 to 5 cm or 8 to 10 cm tall for annual grass and broadleaf weeds whereas yellow nutsedge and glyphosate-resistant corn were 8 to 10 cm tall. All herbicide treatments controlled 2- to 5-cm common cocklebur, Florida beggarweed, jimsonweed, ladysthumb smartweed, Pennsylvania smartweed, pitted morningglory, prickly sida, redroot pigweed, smooth pigweed, and velvetleaf at least 90%. All herbicide treatments except pyrithiobac at either rate controlled 2- to 5-cm common lambsquarters, common ragweed, and tall morningglory at least 90%; pyrithiobac at the lower rate was the only treatment that failed to control entireleaf and ivyleaf morningglory at least 90%. Bromoxynil and pyrithiobac at either rate controlled 2- to 5-cm sicklepod 33 to 68% whereas glufosinate, glyphosate, and sulfostate controlled ≥99%. Glyphosate and sulfosate applied once or twice controlled hemp sesbania less than 70% and volunteer peanut less than 80%. Bromoxynil and pyrithiobac were the least effective treatments for control of annual grass species and bromoxynil controlled Palmer amaranth less than 80%. Glufosinate controlled broadleaf signalgrass, fall panicum, giant foxtail, green foxtail, large crabgrass, yellow foxtail, seedling johnsongrass, Texas panicum, and glyphosate-resistant corn at least 90% but controlled goosegrass less than 60%. Glyphosate and sulfosate controlled all grass species except glyphosate-resistant corn at least 90%. In greenhouse research, goosegrass could be controlled with glufosinate POST plus a late POST-directed treatment of prometryn plus monosodium salt of methylarsonic acid.

Purple (Cyperus rotundus) and Yellow Nutsedge (C. esculentus) Control in Bermudagrass (Cynodon dactylon) Turf1

Field studies were conducted in 1996 and 1997 to determine postemergence control of purple (Cyperus rotundus) and yellow nutsedge (Cyperus esculentus) by single and sequential applications of bentazon, halosulfuron, and sulfentrazone; sequential applications of MSMA; and single applications of imazaquin and imazaquin plus MSMA. Sequential applications of halosulfuron at 70 g ai/ha controlled purple nutsedge more effectively at 10 wk after initial application (WAI) than all other herbicides. Single applications of imazaquin (0.56 kg ai/ha) or imazaquin plus monosodium salt of methylarsonic acid (MSMA, 2.24 kg ai/ha) controlled purple nutsedge adequately 6 WAI (78 and 90%, respectively) but not 18 WAI. Single applications of either halosulfuron (70 g/ha) or imazaquin plus MSMA or sequential applications of either bentazon (1.12 kg ai/ha), MSMA (2.8 kg/ha), or halosulfuron controlled yellow nutsedge greater than 80% by the end of the season in 1996 when nutsedge was in bermudagrass (Cynodon dactylon L.). However, in absence of bermudagrass in 1997, only sulfentrazone or the halosulfuron sequential treatments controlled yellow nutsedge 13 WAI. In 1996, single and sequential applications of halosulfuron reduced viability of purple nutsedge tubers to 33 and 30%, respectively, compared to 84% in the nontreated control. However, herbicide treatments did not reduce tuber viability in 1997. Sulfentrazone (0.28 kg ai/ha) plus MSMA (2.24 kg/ha) and sequential MSMA applications reduced viability of yellow nutsedge tubers to 6 and 31%, respectively, in 1997.Nomenclature: Bentazon, 3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide; halosulfuron, methyl 5-[[(4,6-dimethoxy-2-pyrimidinyl)amino]carbonylami-nosulfonyl]-3-chloro-1-methyl-1-H-pyrazole-4-carboxylate; imazaquin, 2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-quinolinecarboxylic acid; MSMA, monosodium salt of methylarsonic acid; sulfentrazone, N-[2,4-dichloro-5-[4-(difluoromethyl)-4,5-dihydro-3-methyl-5-oxo-1H-1,2,4-triazol-1-yl] phenyl] methanesulfonamide; purple nutsedge, Cyperus rotundus L. #3 CYPRO; yellow nutsedge, Cyperus esculentus L. # CYPES; bermudagrass, Cynodon dactylon (L.) Pers. #CYNDA.Additional index words: Tuber viability, weed management, CYNDA, CYPES, CYPRO.Abbreviations: fb, followed by; MSMA, monosodium salt of methylarsonic acid; NIS, nonionic surfactant; POST, postemergence; WAI, weeks after initial treatment; WP, wettable powder.

Fruiting Response of Cotton (Gossypium hirsutum) to Pyrithiobac

Field experiments were conducted in 1991 and 1992 near Stoneville, MS and Greenville, MS, to determine the impact of pyrithiobac on cotton fruiting, maturity, and yield. Trials were conducted in areas maintained weed-free with standard production practices to optimize yields. Pyrithiobac was applied at 105 or 210 g ae/ha either PRE or POST to cotton in the cotyledon to 2-leaf, 5- to 7-leaf, and matchhead-square (MHS) stages of growth. At one location, monosodium salt of methylarsonic acid (MSMA) and fluometuron plus MSMA were applied as standard comparisons. At the Stoneville location, injury 1 wk after treatment (WAT) with pyrithiobac ranged from 2.5% with 105 g/ha applied at cotyledon to 2-leaf to 26% with 210 g/ha applied at MHS. Injury was transient in nature and was rarely detectable 4 wk after treatment in either year. Injury was not evaluated at the Greenville location. At Stoneville, a reduction in height occurred with MHS applications of pyrithiobac and MSMA. There was no reduction in yield for any treatment compared to the untreated check in 1991 at Stoneville and in both years at Greenville. In 1992 at Stoneville, treatments of 210 g/ha pyrithiobac, MSMA, and fluometuron plus MSMA at all application timings reduced yield. Pyrithiobac at 105 g/ha applied PRE also reduced yield. Greatest yield loss occurred with treatments of MSMA applied at MHS. There were no yield reductions at either location with postemergence application of 105 g/ha pyrithiobac.

Buffalograss Seedling Tolerance to Postemergence Herbicides

In 1992 and 1993, 12 postemergence herbicide treatments were applied to field-grown buffalograss [Buchloe dactyloides (Nutt.) Engelm.] seedlings having 1 to 3 leaves and 2 to 4 tillers, respectively. The only herbicide treatments that did not cause plant injury at 1 or 2 weeks after treatment (WAT) or reduce turf coverage 4 or 6 WAT compared to nontreated plots (in 1992 or 1993) were (in kg·ha–1) 0.6 dithiopyr, 0.8 quinclorac, 2.2 MSMA, and 0.8 clorpyralid. Evaluated only in 1993, metsulfuron methyl (0.04 kg·ha–1) also caused no plant injury or reduction in coverage. Fenoxaprop-ethyl (0.2 kg·ha–1) caused severe plant injury and reduced coverage by >95% at 6 WAT. Dicamba reduced coverage by 11% at 6 WAT in 1992 but not 1993. The chemicals (in kg·ha–1) triclopyr (0.6), 2,4-D (0.8), triclopyr (1.1) + 2,4-D (2.8), 2,4-D (3.1) + triclopyr (0.3) + clorpyralid (0.2), and 2,4-D (2.0) + mecoprop (1.1) + dicamba (0.2) caused plant injury at 1 or 2 WAT in 1992 or 1993, but coverage was similar to that of nontreated turf by 6 WAT. Chemical names used: 3,6-dichloro-2-pyridinecarboxylic acid (clorpyralid); 3,6-dichloro-o-anisic acid (dicamba); (+/–)-2-[4-(2,4-dichlorophenoxy)phenoxy]propanoic acid (diclofop); 3,5-pyridinedicarbothioic acid, 2-(difluoromethyl)-4-(2-methylpropyl)-6-(trifluoromethyl)-S,S-dimethyl ester (dithiopyr); 2-[4-[(6-chloro-2-benzoxazolyl)oxy]phenoxy] propanoate (fenoxaprop-ethyl); 2-(2,4-dichlorophenoxy)propionic acid (mecoprop); methyl 2-[[[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)-amino]carbonyl]amino]sulfonyl]benzoate (metsulfuron methyl); monosodium salt of methylarsonic acid (MSMA); 3,7-dichloro-8-quinolinecarboxylic acid (quinclorac); [(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid (triclopyr); (2,4-dichlorophenoxy) acetic acid (2,4-D).

Creeping Bentgrass Quality following Preemergence and Postemergence Herbicide Applications

Three field experiments were conducted to determine if several preemergence and postemergence herbicides were safe to apply to creeping bentgrass (Agrostis stolonifera L. `Penncross') maintained at putting green height. When dithiopyr was applied at preemergence in late February or early March, the emulsifiable concentrate formulation (≤1.7 kg·ha-1) and granular formulation (≤1.1 kg·ha-1) did not reduce the quality or cover of creeping bentgrass. Applied at preemergence, bensulide plus oxadiazon at 6.7 + 1.7 kg·ha-1 and 13.4 + 3.4 kg·ha-1 reduced turfgrass quality for 2 to 3 weeks and 8 weeks after treatment, respectively. When MON 12051 and monosodium salt of methylarsonic acid (MSMA) (≤0.14 and ≤2.2 kg·ha-1, respectively) were applied at postemergence to creeping bentgrass in early June, the reduction in turfgrass quality varied from slight to moderate for 1 to 2 weeks, but turfgrass fully recovered with no effect on turfgrass cover. Quinclorac applied at postemergence in early June at ≥0.6 kg·ha-1 severely reduced creeping bentgrass quality and cover for ≥8 weeks. Diclofop at 0.6 kg·ha-1 applied to creeping bentgrass in June, July, or August maintained consistently higher quality and cover ratings than when applied at ≥1.1 kg·ha-1. Diclofop applied at 0.6 kg·ha-1 in June and repeated at the same rate in July reduced quality of creeping bentgrass less than when applied at 1.1 kg·ha-1 at any date. Chemical names used: O,O-bis (1-methylethyl) S-{2-[(phenylsulfonyl)amino]ethyl} phosphorodithioate (bensulide); (±)-2-[4-(2,4-dichlorophenoxy)phenoxy]propanoic acid (diclofop); S,S-dimethyl-2-(difluoromethyl)-4-(2-methylpropyl)-6-(trifluoromethyl)-3,5-pyridinedicarbothioate (dithiopyr); methyl-5-{[(4,6-dimethoxy-2-pyrimidinyl)amino] carbonylaminosulfonyl}-3-chloro-1-methyl-1-H-pyrazol-4-carboxylate (MON 12051); 3-[2,4-dicloro-5-(1-methylethoxy)phenyl]-5-(1,1-dimethylethyl)-1,3,4-oxadiazol-2-(3H)-one (oxadiazon); 3,7-dicloro-8-quinolinecarboxylic acid (quinclorac).

Peanut Control in Rotational Crops

Abstract Volunteer peanut (Arachis hypogaea L.) can reduce the effectiveness of crop rotation as a component in a peanut disease management program. Experiments were conducted in three states to evaluate peanut control with glyphosate [N-(phosphonomethyl)glycine] or with herbicides commonly applied postemergence for broadleaf weed control in corn (Zea mays L.) and cotton (Gossypium hirsutum L.). Two sequential applications were needed for acceptable control with corn and cotton herbicides. Greater than 80% control of peanut was achieved with dicamba (3,6-dichloro-2-methoxybenzoic acid) applied early postemergence (EPOST) followed by dicamba or ametryn [N-ethyl-N′-(l-methylethyl)-6-(methylthio)-1,3,5-triazine-2,4-diamine] applied late postemergence (LPOST). MSMA (monosodium salt of methylarsonic acid) applied EPOST followed by oxyfluorfen [2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene] + MSMA LPOST and fluometuron [N,N-dimethyl-N′-[3-trifluoromethyl) phenyl]urea] + MSMA applied EPOST followed by prometryn [N,N′-bis(1-methylethyl)-6-(methylthio)-1,3,5-triazine-2,4-diamine] + MSMA, cyanazine [2-[[4-chloro-6-(ethylamino)-1,3,5-triazin-2-yl]amino]-2-methylpropanenitrile] + MSMA, lactofen {(±)-2-ethoxy-1-methyl-2-oxoethyl 5-[2-chloro-4-(trifluoromethyl)phenoxy]- 2-nitrobenzoate} + MSMA, or oxyfluorfen + MSMA LPOST controlled peanut at least 80%. Single applications of glyphosate at 0.84 to 1.12 kg ae/ha controlled peanut at least 80% and were at least as efficacious as the same total rate of glyphosate applied sequentially.

Buffalograss Tolerance to Postemergence Herbicides

Buffalograss [Buchloe dactyloides (Nutt.) Engelm.] is a turfgrass species traditionally adapted to low-rainfall areas that may incur unacceptable weed encroachment when grown in higher rainfall areas such as Florida. An experiment was performed to evaluate the tolerance of two new buffalograss cultivars, `Oasis' and `Prairie', to postemergence herbicides commonly used for grass, broadleaf, and sedge weed control. Twenty to 40 days were required for each cultivar to recover from treatment with asulam, MSMA, and sethoxydim (2.24, 2.24, and 0.56 kg-ha-l, respectively). Other herbicides used for postemergence grass weed control (metsulfuron, quinclorac, and diclofop at 0.017, 0.56, and 1.12 kg·ha-1, respectively) did not cause unacceptable buffalograss injury. Herbicides used for postemergence broadleaf weed control, triclopyr, 2,4-D, sulfometuron, dicamba (0.56, 1.12, 0.017, and 0.56 kg·ha-1, respectively), and a three-way combination of 2,4-D + dicamba + mecoprop (1.2 + 0.54 + 0.13 kg·ha-1), caused 20 to 30 days of unacceptable or marginally acceptable turfgrass quality, while 20 days were required for `Prairie' buffalograss to recover from atrazine treatments. `Oasis' buffalograss did not fully recover from 2,4-D or 2,4-D + dicamba + mecoprop through 40 days after treatment. Herbicides used for postemergence sedge control, bentazon and imazaquin, caused slightly reduced, but acceptable, levels of turf quality in both cultivars throughout the experiment. Chemical names used: 6-chloro-N-ethyl-N'-(1-methylethyl)-1,3,5-triazine-2,4-diamine (atrazine); methyl[(4-aminophenyl)sulfonyl]carhamate (asulam); 3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide (bentazon); 3,6-dichloro-2-methoxybenzoic acid (dicamba); (±)-2-[4-(2,4-dichlorophenoxy)phenoxy]propanoic acid (diclofop); 2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-quinolinecarboxylic acid (imazaquin); (±)-2-(4-chloro-2-methylphenoxy)propanoic acid (mecoprop); 2-[[[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl]amino]sulfonyl]benzoic acid (metsulfuron); monosodium salt of methylarsonic acid (MSMA); 2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one(sethoxydim); 2-[[[[(4,6-dimethylethyl-2-pyrimidinyl)amino]carbonyl]amino]sulfonyl]benzoic acid (sulfometuron); [(3,5,6-trichloro-2-pyridinyl)oxy]acetic acid (triclopyr); (2,4-dichlorophenoxyl)acetic acid (2,4-D); 3,7-dichloro-8-quinolinecarboxylic acid (quinclorac).

Response of Selected Forage Grasses to Herbicides

AbstractEarly spring applications of herbicides were evaluated for weed control and phytotoxicity to kleingrass (Panicum coloratum L.) during establishment. In 1986, areas treated with MSMA (monosodium salt of methylarsonic acid) at 2.2 and 4.5 kg ha−1 or chlorsulfuron {2‐chloro‐N‐[ [(4‐methoxy‐6‐methyl‐1,3,5‐triazin‐2‐yl) amino] carbonyl] benzenesulfonamide} at 0.018 and 0.035 kg ha−1 reduced weed yield to <900 and increased kleingrass yield to >9300 kg ha−1. Untreated areas produced 5400 and 4300 kg ha−1 of weeds and kleingrass, respectively. In 1988, kleingrass yields were increased only where weeds were removed by hand or MSMA. Bensulide [O,Obis( 1‐methylethyl) S‐[2‐[(phenylsulfonyI) amino] ethyl] phosphorodithioate], butylate [S‐ethyl bis(2‐methylpropyl)carbamothioate], siduron [N‐(2‐methylcyclohexyl)‐N'‐phenylurea], and sulfometuron {2‐[[[[(4,6‐dimethyl‐2‐pyrimidinyl) amino] carbonyl] amino] sulfonyl] benzoic acid) were highly injurious to kleingrass. In 1989, no treatment increased kleingrass yields. In the greenhouse, ‘Selection 75’ kleingrass, common buffelgrass (Cenchrus ciliaris L.), ‘WW‐Spar’ and ‘WW‐Ironmaster’ old world bluestem [Bothriochloa ischaemum (L.) Keng var. ischaemum (Hack.) Celarier and Harlan], ‘Bell’ rhodesgrass (Chloris gayana Kunth), ‘Cowboy’ laurisiagrass (Penniseturn orientale L.), ‘Haskel’ sideoats grama [Bouteloua curtipendula (Michx.) Torr.], ‘Lameta’ Indiangrass (Sorghustrum nutans L.), 'Alamo' switchgrass (Panicum virgatum L.), and ‘Palar’ Wilman lovegrass (Eragrosfis superba Peyn.) were treated. Based on seedling weight, most grasses tolerated butylate, MSMA, 2,4‐D [(2,4‐dichlorophenoxy) acetic acid], chlorsulfuron, and metsulfuron {2‐[[[[(4 methoxy‐6‐methyl‐1,3,5‐triazin‐2‐yl)amino] carbonyl] amino] sulfonyl] benzoic acid]. Buffelgrass, Indiangrass, and old world bluestem tolerated sulfometuron. Atrazine [6‐chloro‐N‐ethyl‐N'‐(‐methylethyl)‐ 1,3,5‐triazine‐2,4‐diamine] and propazine [6‐chloro‐N,N'‐ bis(l‐methylethyl)‐l,3,5‐triazine‐2,4diamine] were sometimes injurious, but bensulide and siduron were highly injurious to most grasses.

Resistance of Common Cocklebur (Xanthium strumarium) to the Organic Arsenical Herbicides

The presence of a common cocklebur (Xanthium strumariumL. # XANST) population resistant to organic arsenical herbicides was confirmed in three adjoining counties of South Carolina's ten-county cotton-growing region, but little evidence of resistance was found in the remaining seven counties. This population was resistant to both disodium salt of methylarsonic acid (DSMA) and monosodium salt of methylarsonic acid (MSMA) but not to herbicides from nine other chemical groups. A much greater level of resistance was apparent in the field than under greenhouse conditions and larger plants were more resistant than small plants.

Purple Nutsedge (Cyperus rotundus) Control with Imazaquin in Warm-Season Turfgrasses

Postemergence applications of imazaquin {2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-quinolinecarboxylic acid} controlled higher levels of purple nutsedge (Cyperus rotundusL. # CYPRO) in common bermudagrass [Cynodon dactylon(L.) Pers.] and hybrid bermudagrass (′Tifgreen’ and ‘Tifdwarf′,C. dactylon×C. transvaalensisBurtt-Davy) than monosodium salt of methylarsonic acid (MSMA). Control was better at 560 or 840 g ai/ha of imazaquin than at lower rates. Postemergence applications of imazaquin plus 2240 g ai/ha of MSMA controlled more purple nutsedge than equivalent rates of imazaquin alone. Preemergence applications of imazaquin were not effective. Bermudagrass discoloration was observed in some experiments on turfs mowed at a height of 1.3 cm or less but usually disappeared within 2 to 3 weeks, especially when MSMA was used in combination with imazaquin. No injury was observed on bermudagrasses, zoysiagrass (Zoysia japonicaSteud. ‘Meyer′), St. Augustinegrass [Stenotaphrum secundatum(Walt.) Ktze. ‘Raleigh′], and centipedegrass [Erernochloa ophiuroides(Munro) Hack.] maintained at mowing heights above 1.3 cm.

Interaction of Fluometuron and MSMA with Sethoxydim and Fluazifop

Field experiments were conducted to determine the effects of tank-mixing fluometuron {N,N-dimethyl-N′-[3-(trifluoromethyl)phenyl] urea} or MSMA (monosodium salt of methylarsonic acid) with sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} or the butyl ester of fluazifop {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl]oxy] phenoxy] propanic acid} on cotton (Gossypium hirsutumL.) tolerance and large crabgrass [Digitaria sanguinalis(L.) Scop. # DIGSA] control. Postemergence (over-the-top) application of 1.7 kg ai/ha of fluometuron reduced cotton lint yield 17 to 23% in three of four tests. No yield reduction resulted from postemergence application of 1.1 kg ae/ha of MSMA. Tank-mixing 0.1 or 0.2 kg ai/ha of sethoxydim or 0.1 or 0.2 kg ae/ha of fluazifop with fluometuron or MSMA did not alter the effect of fluometuron or MSMA on cotton yield. Tank mixtures of 1.1 to 2.2 kg/ha of fluometuron plus sethoxydim or fluazifop were antagonistic. No antagonism was observed when fluometuron was applied 3 days before or 6 h following sethoxydim or fluazifop application. Tank-mixing 1.1 or 2.2 kg/ha of MSMA with sethoxydim or fluazifop initially reduced control of large crabgrass. Antagonism was not observed at 4 weeks after tank-mix application of MSMA plus sethoxydim, and was observed in only one of three experiments 4 weeks following tank-mix application of MSMA plus fluazifop. When antagonism was observed with tank mixtures of fluazifop plus MSMA, sequential application of MSMA 1 to 7 days before application of fluazifop did not overcome the antagonism. No antagonism occurred when MSMA was applied 6 or more hours after fluazifop application.

Efficacy of Bentazon and MSMA as Affected by a Humic Acid-Type Polymeric Polyhydroxy Acid Adjuvant

Foliar applications of14C-bentazon [3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] with PPA (polymeric polyhydroxy acid) at 1 or 2% (v/v) or nonoxynol (9.5 POE) [α-(p-nonylpheny1)-ω-hydroxypoly(oxyethylene)] at 1% (v/v) or mixtures of PPA and nonoxynol did not increase absorption or translocation of14C-bentazon in soybeans [Glycine max(L.) Merr. ‘Lee 74′] or common cocklebur (Xanthium strumariumL. # XANST). PPA alone at 1 to 2% (v/v) did not significantly affect absorption or translocation of14C-bentazon in smooth pigweed (Amaranthus hybridusL. # AMACH), but PPA with nonoxynol significantly increased translocation out of the treated leaf. Both PPA and nonoxynol decreased absorption and movement of14C-MSMA [monosodium salt of methylarsonic acid] out of the treated leaf of johnsongrass [Sorghum halepense(L.) Pers. # SORHA]. In greenhouse research, PPA at 0.25 and 0.5% (v/v) did not increase the level of control of common cocklebur obtained following postemergence applications of bentazon at 0.24 and 0.48 kg ai/ha. Similarly, PPA at 0.25 and 0.50% (v/v) did not increase the toxicity of MSMA at 0.3 and 0.6 kg ai/ha to either johnsongrass or common cocklebur.

Repeated Annual Applications of Herbicides for Control of Rhizome Johnsongrass (Sorghum halepense) in Cotton (Gossypium hirsutum)

When postemergence applications of sethoxydim {2-[1-(ethoxyimino) butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} were compared with DSMA (disodium salt of methylarsonic acid), MSMA (monosodium salt of methylarsonic acid), and glyphosate [N-(phosphonomethyl)glycine] for control of johnsongrass [Sorghum halepense(L.) Pers. # SORHA] in cotton (Gossypium hirsutumL. ‘Acala SJ-2′), repeated annual applications of sethoxydim were more successful than other herbicides in protecting yields of cotton and reducing populations of rhizome johnsongrass over time. After the first year of treatment with sethoxydim in 1982, when an 18% yield loss of cotton occurred, populations of rhizome johnsongrass were reduced to the extent that they were no longer a threat to yields in plots treated with sethoxydim in 1983 and 1984. Although DSMA and glyphosate improved yields when compared to cultivated control plots, substantial yield losses occurred every year, and populations of johnsongrass remained unchanged after 3 yr of treatment. Averaged over 3 yr, plots treated with sethoxydim produced 94% as much cotton as weed-free plots, compared to 60 and 45% for plots treated with glyphosate and DSMA/MSMA, respectively.

Factors Affecting Degradation of MSMA in Soil

The effects of herbicide concentration, soil water content, and temperature on the fate and degradation of the monosodium salt of methylarsonic acid (MSMA) were evaluated in four soils. Available arsenicals were extracted, purified, and separated using reversed-phase high-performance liquid chromatography (HPLC). Residual MSMA was determined with a graphite furnace atomic absorption spectrophotometer at 193.7 nm. Initial loss of MSMA was rapid, and degradation followed first-order kinetics. The rate of change of the rate constant was temperature dependent only at soil water contents less than field capacity. MSMA dissipation was significantly faster in finer textured soils with continuous flooding and under controlled laboratory conditions (<180 days) than under field (ca. 350 days) conditions. Also, in finer textured soils, degradation of MSMA resulted in significant increases in arsenate and cacodylic acid (dimethyl arsinic acid) over native levels under flooded conditions. However, MSMA treatments contributed only a small fraction to total soil arsenic which dissipated to original concentrations by 120 days. The results indicate that under present recommended use patterns it is highly unlikely that MSMA will accumulate in the environment or carry over from one growing season to the next.

Effect of Cotton (Gossypium hirsutum) Herbicide Carryover on Subsequent Crops

The residual effect of three cotton (Gossypium hirsutumL.) herbicide programs, including the use of no herbicides, a minimum program consisting of fluometuron {N,N-dimethyl-N′-[3-(trifluoromethyl)phenyl] urea} and MSMA (monosodium salt of methylarsonic acid), and an intensive program consisting of trifluralin [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine], fluometuron, MSMA, and linuron [N′-(3,4-dichlorophenyl)-N-methoxy-N-methylurea], were evaluated from 1976 to 1982. Herbicide injury to wheat (Triticum aestivumL.) and hairy vetch (Vicia villosaRoth.) on three soils showed carryover effects in the following sequence: Sharkey silty clay > Dundee silt loam > Loring silt loam. The intensive program was the most injurious on the Sharkey silty clay. The effects of the two herbicide programs were nearly equal on the Dundee and Loring silt loams. Possible replacement crops for cotton, such as grain sorghum [Sorghum bicolor(L.) Moench.] and corn (Zea maysL.) suffered the least damage from carryover; rice (Oryza sativaL.), soybeans [Glycine max(L.) Merr.] and cucumber (Cucumis sativisL.) suffered severe damage. Greenhouse bioassays generally confirmed field results, and fluometuron appeared to be the major component of carryover.