Efficacy of EPTC (S-ethyl dipropylcarbamothioate), butylate [S-ethyl bis(2-methylpropyl)carbamothioate], vernolate (S-propyl dipropylcarbamothioate), and cycloate (S-ethyl cyclohexylethylcarbamothioate) applied with dichlormid (N,N-diallyl-2,2-dichloroacetamide), and the former three herbicides applied with dichlormid and dietholate (O,O-diethyl-O-phenol phosphorothioate) for wild proso millet (Panicum miliaceum L. ssp. ruderale (Kitagawa) Tzevelev. # PANMI) control in corn (Zea mays L.) was evaluated in fields previously treated with EPTC + dichlormid or EPTC + dichlormid + dietholate. Cycloate + dichlormid usually controlled millet regardless of prior herbicide use. But EPTC + dichlormid was less effective than on soils not previously treated with the herbicides, suggesting enhanced soil biodegradation. The use of EPTC + dichlormid with row cultivation or applications of selected herbicides improved millet control. Following prior use of EPTC + dichlormid, wild proso millet control was improved by the addition of dietholate to EPTC + dichlormid and vernolate + dichlormid but not butylate + dichlormid. In dissipation studies using soils previously treated with EPTC + dichlormid, the relative order of herbicide persistence was EPTC + dichlormid < vernolate + dichlormid < butylate + dichlormid < EPTC + dichlormid + dietholate < vernolate + dichlormid + dietholate = butylate + dichlormid + dietholate < cycloate + dichlormid. When EPTC + dichlormid + dietholate was applied to soils previously treated with that mixture, wild proso millet control was again reduced. Dissipation studies confirmed that dietholate slowed biodegradation of EPTC in soils previously treated with EPTC + dichlormid but not with EPTC + dichlormid + dietholate.

Ryegrass (Lolium multiflorum Lam. # LOLMU) control in wheat (Triticum aestivum L.) using chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl) amino] carbonyl] benzenesulfonamide} at 35 g ai/ha was significantly higher when applied preemergence (pre) than early postemergence (poe) to ryegrass with two to four leaves and wheat with three to five tillers. Metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one] applied at 420 g ai/ha early poe controlled more than 95% of the ryegrass, but control was unacceptable when the same rate was applied late poe when the ryegrass was at midtiller and wheat at full tiller. Wheat leaf burn, stunting, and stand reduction occurred where metribuzin was applied early poe but yields were not affected. Ryegrass control was excellent where diclofop {(±)-2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid} was applied early poe at 560 g ai/ha. Wheat yields, averaged over years, for early poe applications of chlorsulfuron at 35 g/ha, metribuzin at 280 and 420 g/ha, and diclofop at 560 g/ha were 22, 22, 24, and 20% higher, respectively, than the untreated stands. Injury associated with the herbicide treatments was not observed on soybeans [Glycine max (L.) Merr.] planted following wheat.

Norflurazon [4-chloro-5-(methylamino)-2-(3-(trifluoromethyl)phenyl)-3(2H)-pyridazinone] persistence in five Georgia soils after application to the same plots in 1982 and 1983 was characterized by rapid initial degradation followed by slow loss of the herbicide. The rate of norflurazon loss at each location for each year was not affected by application rate (1.7 or 3.4 kg ai/ha). Relative rates of norflurazon loss were Dothan loamy sand ≥ Greenville sandy clay loam ≥ Rome gravelly clay loam = Appling coarse sanely loam > Bradson clay loam. The rate of dissipation was slower in 1983 than 1982 in the Greenville and Appling soils. Cool and/or dry environmental conditions combined with higher soil organic matter content caused slower herbicide loss. Norflurazon residue 1 yr after treatment in all soils was greater in 1983 than in 1982. Significant injury to grain sorghum [Sorghum bicolor (L.) Moench. ‘BR 64’) was observed in the spring of 1984 at all locations in all plots that were treated with norflurazon for the previous two seasons. The degree of injury corresponded to the concentration of norflurazon detected at that sampling date. Leaching did not appear to be an important method of norflurazon loss.

In field and greenhouse studies, tank mixing 0.3 and 0.4 kg ai/ha of the butyl ester of fluazifop {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy]propanoic acid} with 0.4 kg ai/ha of acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid} reduced control of large crabgrass [Digitaria sanguinalis (L.) Scop. # DIGSA] and itchgrass (Rottboellia exaltata L.f. # ROOEX) compared to fluazifop applied alone in soybeans [Glycine max (L.) Merr.]. Less antagonism between the two herbicides was observed in a year when conditions were optimum for large crabgrass control with fluazifop. Application of acifluorfen 1 to 3 days before application of fluazifop decreased large crabgrass control. Antagonism between fluazifop and acifluorfen was avoided when fluazifop was applied 3 to 5 days before acifluorfen. No antagonism was observed when fluazifop at 0.3 or 0.4 kg/ha was tank mixed with acifluorfen at 0.4 kg/ha for control of itchgrass. Itchgrass was more susceptible to fluazifop than large crabgrass.

Experiments in controlled-environment chambers indicated that high temperature, 30 C, increased the phytotoxicity of bromoxynil (3,5-dibromo-4-hydroxybenzonitrile) to wild mustard (Sinapis arvensis L. # SINAR) and redroot pigweed (Amaranthus retroflexus L. # AMARE) compared to low temperature, 10 C, during and after treatment. Bromoxynil phytotoxicity generally was higher at relative humidities of 90 to 95% compared to 40 to 60%, but relative humidity had less influence on bromoxynil phytotoxicity than did temperature. A simulated rain immediately after bromoxynil treatment reduced control of both species, but the reduction was of no practical importance for wild mustard. The data indicate that wild mustard and redroot pigweed control would be reduced by bromoxynil application during a period of low temperatures or to plants in advanced growth stages.

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.

Honey mesquite (Prosopis glandulosa Torr. # PRCJG) was treated with four herbicides at 1.1 kg ae/ha at 14 dates from April 30 through September 23 over a 2-yr period. Overall, clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) was the most effective herbicide, killing 80% or more of the honey mesquite at most dates. Picloram (4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid), triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid}, and 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid] were less effective than clopyralid. Honey mesquite control was correlated with Julian day of year sprayed, 15 plant, 11 environmental, and 8 herbicide concentration variables. Most effective control was negatively correlated with Julian day of year sprayed and new xylem ring thickness. Control was positively correlated with total daily apparent photosynthesis, upward methylene blue dye movement in the xylem, and herbicide concentration in the xylem 3 days after spraying. The only environmental variable of 11 measured that was significantly correlated with honey mesquite control was soil water and that was only with picloram. The concentration of herbicide in the stem was highest for clopyralid, followed by picloram, and then by 2,4,5-T and triclopyr, which were about equal. Variables most useful in regression equations for predicting control with herbicides were total daily apparent photosynthesis and rate of upward movement of methylene blue dye. Variables most incorporated into regression equations relating honey mesquite control with herbicide content were herbicide concentrations in the xylem 3 or 30 days after treatment.

Various chemical treatments were evaluated over two growing seasons for control of triazine-resistant common lambsquarters (Chenopodium album L. # CHEAL) and for control of a triazine-resistant infestation containing both redroot pigweed (Amaranthus retroflexus L. # AMARE) and Powell amaranth (A. powellii S. Wats. # AMAPO). Atrazine [6-chloro-N-ethyl-N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine], cyanazine {2-[[4-chloro-6-(ethylamino)-1,3,5-triazin-2-yl] amino]-2-methylpropanenitrile}, and metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one] provided unsatisfactory control of these biotypes. Satisfactory control of common lambsquarters was obtained with preemergence applications of pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine] or dicamba (3,6-dichloro-2-methoxybenzoic acid), or postemergence applications of dicamba, bromoxynil (3,5-dibromo-4-hydroxybenzonitrile), or bentazon [3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide]. Satisfactory control of pigweed was obtained with preemergence applications of alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide] or postemergence treatments of dicamba, bromoxynil, or 2,4-D [(2,4-dichlorophenoxy) acetic acid].

Established stands of alfalfa (Medicago sativa L.) at two field locations were treated at one date in the fall with pronamide [3,5-dichloro (N-1,1-dimethyl-2-propynil) benzamide] at 0.8 and 1.6 kg ai/ha and at two dates in the spring with sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} at 0.3 and 0.6 kg ai/ha for the control of quackgrass [Agropyron repens (L.) Beauv. # AGRRE]. Herbicide efficacy was compared by measuring botanical and chemical composition and yield of forage. Both chemicals suppressed quackgrass in first-cutting herbage. While sethoxydim at the higher rate was equivalent to pronamide for increasing the proportion of alfalfa in forage, pronamide was superior for increasing seasonal total yield. Late postemergence applications of sethoxydim were more effective for quackgrass regrowth control than earlier spring applications. Controlling quackgrass in late spring resulted in lower crude protein (CP) content in first-cutting forage than did controlling it in fall. Alfalfa competing with untreated quackgrass had a lower CP content than where quackgrass was controlled with herbicides. All herbicide treatments reduced the neutral-detergent fiber (NDF) of the herbage. As measured by the acid-detergent fiber (ADF) concentration of alfalfa, sethoxydim slightly retarded spring growth of the legume.

Response of grain sorghum [Sorghum bicolor (L.) Moench. ‘BR 64’] to norflurazon [4-chloro-5-(methylamino)-2-(3-(trifluoromethyl)phenyl)-3(2H)-pyridazinone] and fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl) phenyl]-4(1H)pyridinone} and the effect of previous treatment on the persistence of herbicide activity in five soils were determined in the greenhouse. Relative phytotoxicity of fluridone in the soils was ordered as Greenville sandy clay loam > Appling coarse sandy loam > Dothan loamy sand = Rome gravelly clay loam > Bradson clay loam. Phytotoxicity of norflurazon was ordered as Greenville = Appling = Dothan > Rome > Bradson. Fluridone was more phytotoxic than norflurazon. Field soil that has been previously treated with norflurazon or fluridone (500 days earlier at 1.7 kg ai/ha) still had low concentrations of each herbicide present at the time of retreatment in the greenhouse. Previous treatment of norflurazon did not affect the rate of decline in activity in any of the soils compared to previously nontreated soils except for Appling. Significantly higher concentrations of norflurazon remained in all previously treated soils 297 days after treatment (DAT) compared to previously nontreated soil. Residual carryover of norflurazon was greater in the Bradson soil (2.8% O.M.) than soils having less than 2% O.M. Fluridone dissipation was significantly faster in previously treated soil than in previously nontreated soil, indicating enhanced microbial degradation of the herbicide.

The influence of surfactant type and concentration on the efficacy of asulam {methyl [(4-aminophenyl) sulfonyl] carbamate} for controlling rhizomatous johnsongrass [Sorghum halepense (L.) Pers. # SORHA] was evaluated in field and greenhouse studies. Under field conditions, nonoxynol (9 to 10 POE) [α-lp-nonylphenyl)-w-hydroxypoly (oxyethylene)] applied at concentrations of 6% (v/v) with asulam at 2.8 kg ai/ha reduced rhizomatous johnsongrass biomass by 35%, with no consistently significant difference in asulam's performance between surfactant concentrations of 0 and 3% (v/v) being observed. Asulam applied with nonoxynol at concentrations of 3 and 6% (v/v) reduced sugarcane (Saccharum interspecific hybrids) yields and significantly offset any advantages from increased johnsongrass control. In greenhouse studies, where johnsongrass foliage was washed either 0, 1, 6, 24, or 48 h after treatment (HAT), the degree of johnsongrass control with asulam was generally not affected by the type of surfactant (paraffin-base petroleum oil-surfactant blend or alcohol-surfactant-water mixture) used. At least 48 h was needed to insure adequate basipetal translocation, hence maximum inhibition of rhizome regrowth with asulam applied alone. Increasing the surfactant concentration shortened this interval to 48 h (0.25%) to 24 h (0.5 to 1%) to 6 h (3%) to 1 h (6%).

In greenhouse studies, Fusarium lateritium Nees ex Fr. was effective in suppressing the growth of velvetleaf (Abutilon theophrasti Medic. # ABUTH) and prickly sida (Sida spinosa L. # SIDSP). Sprays containing conidia of the fungus and fungus-infested sodium alginate-kaolin clay granules controlled both weeds in corn (Zea mays L.), cotton (Gossypium hirsutum L.), and soybeans [Glycine max (L.) Merr.] without causing a reduction in dry weight of the crops. In field tests, postemergence foliar applications of the fungus controlled velvetleaf and prickly sida 40 and 80%, respectively, in 1982, but controlled only 27 and 34% of velvetleaf and prickly sida, respectively, in 1983. Preemergence applications of the fungus in the granule formulation controlled velvetleaf and prickly sida 46 and 59%, respectively, in 1982. In 1983, this treatment controlled the weeds 35 and 38%, respectively.

The phytotoxicity of seven herbicides after soil application was determined in the field and greenhouse. Clopropoxydim {(E,E)-2-[1-[[(3-chloro-2-propenyl)oxy] imino] butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one}, sethoxydim {2-[1-(ethoxyimino)butyl]-5-(2-ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one}, the methyl ester of haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy]propanoic acid} applied to soil at 0.21 kg/ha, and the methyl ester of diclofop {(±)-2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid}applied to soil at 1.12 kg/ha were phytotoxic to oats (Avena sativa L. ‘Moore’) in the field and greenhouse. These rates are equivalent to postemergence use rates of these herbicides. DPX-Y6202 {2-[4-[(6-chloro-2-quinoxalinyl)oxy] phenoxy] propanoic acid} and the butyl ester of fluazifop {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl]oxy] phenoxy] propanoic acid} applied to soil at 0.84 kg/ha or greater were phytotoxic to oats. The ethyl ester of fenoxaprop {(±)-2-[4-[(6-chloro-2-benzoxazolyl)oxy] phenoxy] propanoic acid} soil applied exhibited very limited phytotoxicity to oats. Oat stands were reduced when oats were seeded into soil treated with clopropoxydim, sethoxydim, haloxyfop, diclofop, DPX-Y6202, fluazifop, and fenoxaprop, with the amount of stand reduction decreasing from clopropoxydim to fenoxaprop. Oat fresh weight reductions were greatest with all herbicides when the herbicides were in contact with all underground parts (shoots, seeds, and roots). Oat fresh weight reductions were greater when either the shoot or seed of the germinating oat plants were exposed to the herbicides compared to root exposure. Foxtail millet (Setaria italica L. ‘Siberian’) was more susceptible to injury than oats or wheat (Triticum aestivum L. ‘Len’) when seeded into soil treated with any one of the seven postemergence grass control herbicides.

Imazaquin {2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-quinolinecarboxylic acid} sorption and mobility were studied in five Alabama soils ranging from sandy loam to clay. Techniques included thinlayer soil chromatography, batch equilibrium, and soil solution recovery. Imazaquin was mobile in all soils with Rf values of 0.8 to 0.9. Sorption based on batch equilibrium was minimal with Kd values ranging from 0.001 to 0.21. The soil solution recovery technique was used to evaluate imazaquin sorption in each soil as influenced by imazaquin concentration, wetting and drying, and pH. As herbicide concentration added to the soils was increased from 0.1 to 10 mg/kg, the amount of 14C-imazaquin in soil solution increased. Temporarily drying each soil to 25 or 50% of field capacity resulted in maximum sorption of imazaquin. Lowering the pH enhanced sorption in all soils such that the amount of imazaquin in solution ranged from 38 (low pH) to 100% (high pH). Soil sorption appeared to be governed by the pH-dependent charge surfaces from aluminum and iron oxyhydroxides (specifically hematite and gibbsite) and kaolinite.

A root washer was constructed which rapidly separated Canada thistle [Cirsium arvense (L.) Scop. # CIRAR] roots larger than 1.3-mm diam with 96% or greater efficiency from cohesive clay soil. The washer removed 93 ± 15% of 43 200 cm clay soil from Canada thistle roots in 2 h. Small residual soil clods and organic debris were removed by hand after washing. The washing action did not damage the root system. From 4 to 6 h were required to wash the large Canada thistle roots from an equivalent volume of clay soil by hand, without using the washer. Rhizomes, seeds, and tubers also may be separated from soil with the washer. The tank and frame of this washer are durable, and moving parts such as bearings can be replaced easily.

Experiments were conducted over 4 yr to investigate the effects of four postemergence herbicides on soybean [Glycine max (L.) Merr. ‘Williams 79’] yield under weed-free conditions. Bentazon [3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide], acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid}, and naptalam/dinoseb {2-[(1-naphthalenylamino)carbonyl] benzoic acid}/[2-(1-methylpropyl)-4,6-dinitrophenol] alone and in combination with 2,4-DB [4-(2,4-dichlorophenoxy) butyric acid] applied to soybeans at the V3 and V5 soybean growth stages caused early crop injury, but soybeans outgrew most of the injury by 21 days and there was no effect on yield. Bentazon plus 2,4-DB with or without adjuvant did not affect the yield of five soybean cultivars tested.

Acetochlor [2-chloro-N-(ethoxymethyl)-N-(2-ethyl-6-methylphenyl)acetamide], alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide], and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] were applied in 280 L of water/ha to plots covered with 0 to 6720 kg/ha of wheat (Triticum aestivum L.) straw. At straw levels of 1120 kg/ha or greater, 50% or less of the applied herbicides were received by the soil surface before irrigation. Sprinkle irrigation (1.3 cm) washed 15 to 20% of the originally applied herbicide into the soil regardless of straw level. More metolachlor was retained on the straw than acetochlor or alachlor. Analysis of the wheat straw indicated that little water-extractable herbicide remained for all herbicides. Initial herbicidal activity on grain sorghum [Sorghum bicolor (L.) Moench.] was reduced by the presence of wheat straw at the time of application, with acetochlor being least affected and alachlor most affected. Ten days after treatment, less than 10% of the original alachlor and acetochlor remained in the soil. When planted at this time, grain sorghum response was inversely related to the amount of straw mulch that was originally present. Metolachlor residues in the soil on day 10 were 11 to 26% of that on day 0 and there was comparably less reduction in activity on grain sorghum.

Total alkaloid concentration, percentage water, crude protein, and neutral detergent fiber in velvet lupine (Lupinus leucophyllus Dougl. # LUPLE) were monitored for 3 weeks following application of herbicides registered or soon to be registered for rangeland use. Picloram (4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid), dicamba (3,6-dichloro-2-methoxybenzoic acid), and clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) caused some signs of epinasty but did not kill velvet lupine. Total alkaloid concentration and nutrient quality of velvet lupine leaves treated with these herbicides was not significantly different from untreated plants. Esters of 2,4-D [(2,4-dichlorophenoxy)acetic acid] and 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid] and triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy]acetic acid} killed most velvet lupine plants and caused a subsequent decrease in total alkaloid concentration, crude protein, and water content as the plants desiccated. Herbicides that effectively killed velvet lupine decreased alkaloid levels, thus lowering the potential for increased livestock poisoning.

Corn (Zea mays L.) grain yield was measured in a 5-yr study at two locations in central Ohio in relationship to johnsongrass [Sorghum halepense (L.) Pers. # SORHA] populations infesting the plots. Herbicide treatments were EPTC + R-25788 (S-ethyl dipropyl carbamothioate) + (N,N-diallyl-2,2-dichloroacetamide) at 6.7 kg ai/ha to corn in a monoculture and in a 3-yr rotation of winter wheat (Triticum aestivum L.), corn, and soybeans [Glycine max (L.) Merr.], with each crop being grown each year. There were large increases in johnsongrass populations in the monocultures during the course of the 5-yr study, and corn grain yield fell to zero, even though ear formation was not greatly reduced. Conversely, johnsongrass populations in the rotation were low and maize grain yields and numbers of ears remained high. The differential in grain yields between the two treatments was apparently due chiefly to lack of pollination or kernel development, since ears were formed in approximately equal numbers, except for the last year.

Research was conducted to determine the effect of winter wheat (Triticum aestivum L.) straw mulch level on weed control in a winter wheat-ecofallow corn (Zea mays L.)-fallow rotation at North Platte and Sidney, NE, in 1981 and 1982. Wheat straw mulch was established at 0, 1.7, 3.4, 5.1, and 6.8 Mg/ha in stubble fields. After application of 1.5 times the recommended rate at corn planting, metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] concentration remained higher in unmulched soil than in mulched soil for more than 4 months, due to interception of metolachlor by the mulch. Even though the amount of metolachlor in the soil was reduced by mulch, weed control was not reduced and increased with increasing mulch level. Thus, increasing metolachlor rate was not necessary to maintain adequate weed control in no-till winter wheat stubble since mulch itself provided some measure of weed control.