Chloroacetamide and thiocarbamate herbicides have many properties in common: both herbicide classes are effective only as preemergence herbicides; they inhibit early seedling growth and cause similar injury symptoms in susceptible species; they are detoxified in plants by glutathione conjugation; they have a similar spectrum of selectivity; they can be applied safely in certain susceptible grass crops when applied with antidotes; and they can inhibit the synthesis of lipids, isoprenoids, and other metabolic processes requiring coenzyme A. It can be hypothesized that these similarities are due to the ability of the chloroacetamides and the sulfoxide of thiocarbamates to bind covalently to enzymes, coenzymes, or metabolic intermediates containing sulfhydryl (-SH) groups.

Field experiments were conducted to determine the influence of growth stage on tolerance of seeded tomatoes (Lycopersicon esculentum Mill.) and of eastern black nightshade (Solanum ptycanthum Dun. #3 SOLPT) to the sodium salt of acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid} at low use rates. Tomatoes as young as the 2 true-leaf stage exhibited some tolerance to acifluorfen at rates of 0.14 kg ae/ha and less. Rates of 0.28 and 0.56 kg/ha caused increased phytotoxicity; however, yield was not greatly reduced. At the 8-leaf stage, foliar injury was slight and existed only at the highest rates tested; however, tomato yields were reduced. Control of black nightshade at the 2-leaf stage was acceptable at rates as low as 0.14 kg/ha. When nightshade was at the 5-leaf stage, 0.28 and 0.56 kg/ha rates provided acceptable control − 87% and 96%, respectively. Nightshade in the 10-leaf stage was not controlled effectively at rates below 0.56 kg/ha.

In 1983 and 1984, 20 commercial soybean [Glycine max (L.) Merr.] cultivars were field tested for their response to fluchloralin [N-(2-chloroethyl)-2,6-dinitro-N-propyl-4-(trifluoromethyl)benzenamine], metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-l,2,4-triazin-5(4H)-one], and vernoiate [S-propyl dipropylcarbamothioate]. Recommended rates for the herbicides were 1.1, 0.4, and 2.8 kg ai/ha, respectively. Each herbicide was applied at recommended (lx), 2x, and 4x rates in both years with an 8x rate added in 1984. Plant height, vigor, and injury were used to determine herbicide effects. Differences existed among cultivars, herbicides, and rates. Increased herbicide rates generally resulted in reduced plant height and vigor and increased plant injury. Cultivars tolerant to the three herbicides included Cumberland, Essex, FFR 560, NAPB 420, and Pixie.

Experiments were conducted in the greenhouse and in the field to determine the influence of flax (Linum usitatissimum L.) seeding depth on tolerance to trifluralin [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine]. Flax stand and fresh weight generally decreased as flax seeding depth increased within or below trifluralin-treated soil. Seeding flax below a trifluralin-treated soil layer did not increase tolerance to trifluralin. Although 0.8 kg ai/ha of trifluralin reduced stand when flax was seeded 3 to 6 cm deep in the field, seed yield remained constant.

When tank mixed with certain boadleaf-selective herbicides, fluazifop {(+)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid}, sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one}, haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid}, and fluazifop-P {(R)-2-[4-[[5-trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} were less effective in controlling two annual grasses, Texas panicum (Panicum texanum Buckl. #3 PANTE) and large crabgrass [Digitaria sanguinalis (L.) Scop. # DIGSA]. These herbicides were applied alone or were combined with the broadleaf-selective herbicides bentazon {3-(1-methylethyl)-(1H)-2,l,3-benzothiadiazin-4(3H)-one-2,2-dioxide} and/or 2,4-DB [4-(2,4-dichlorophenoxy)butanoic acid]. The herbicide combinations controlled smooth pigweed (Amaranthus hybridus L. # AMACH) and yellow nutsedge (Cyperus esculentus L. #CYPES). Increasing the rates of the grass-selective herbicides in the mixture reduced the adverse effects of 2,4-DB or bentazon.

Experiments were conducted to determine the energy requirements and the most effective rotary tiller configuration for incorporating cyanazine {2-[[4-chloro-6-(ethylamino)-1,3,5-triazin-2-yl] amino]-2-methylpropanenitrile} on an 18-cm band centered on top of the previous year's corn (Zea mays L.) ridge. When the rotary tiller was operated full width at a 10-cm depth, the least cyanazine concentration was found in the center of the ridge, and the greatest concentration was found between ridges. The treatment having the greatest cyanazine concentrations in the center of the ridge and the least in the inter-row between ridges consisted of a ridge cleaner, a cyanazine application, and the rotary tiller configured to till a. 30-cm strip on the center of the ridge with a rotor enclosure. Energy requirements for operating the rotary tiller increased as the depth of operation increased, and the 10-cm depth of operation required less energy than two passes with a tandem disk.

Green and yellow foxtail [Setaria viridis (L.) Beauv. #3 SETVI and S. glauca (L.) Beauv. #SETLU] seed germination after 14 days were similar at 15, 20, and 25 C. However, at 10, 30, and 35 C, green foxtail seed germination was higher than that of yellow foxtail, indicating that temperature extremes influenced green foxtail seed germination less than that of yellow foxtail. Seed germination of both species was initiated at about the same time; however, green foxtail seed germinated 1 to 2 days faster than yellow foxtail at all temperatures. After 72 h in −4 bars osmotic potential solution at 25 C, green foxtail seed germination was 70% compared to 12% for yellow foxtail, suggesting that green foxtail seed may germinate more rapidly than yellow foxtail seed in soils with limited moisture.

Sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio) propyl]-3-hydroxy-2-cyclohexen-1-one} at 0.34 kg ai/ha, fluazifop {(+)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} at 0.13 kg ai/ha, and SC-1084 {3-hydroxy-4-[4-[[5-trifluoromethyl)-2-pyridinyl] oxy] phenoxy] pentanoic acid} at 0.28 kg ai/ha controlled ‘Tifway’ bermudagrass [Cynodon transvaalensis Burtt-Davy #3 CYNTR] x [Cynodon dactylon (L.) Pers. # CYNDA] nearly 100% when applied for 2 consecutive years. Tall fescue (Festuca arundinacea Schreb. ‘Ky 31’ # FESAR) tolerated fluazifop at 0.13 kg/ha and SC-1084 at 0.07 to 0.28 kg/ha; however, centipedegrass [Eremochloa ophiuroides (Munro) Hack, ‘common’ #ERLOP] and zoysiagrass (Zoysia japonica Steud. # ZOYJA x Zoysia tenuifolia Willd. ex trin. ‘Emerald’ #ZOYTE did not tolerate these treatments. Centipedegrass tolerated sethoxydim, zoysiagrass tolerance was intermediate, and tall fescue was injured severely. Sethoxydim at 0.22 kg/ha discolored leaves of zoysiagrass, but the turf recovered fully. Thus, bermudagrass, when mixed with either tall fescue, centipedegrass, or zoysiagrass, can be controlled selectively with herbicides applied postemergence.

The effect of common lambsquarters (Chenopodium album L. #3 CHEAL) density on spring barley (Hordeum vulgare L. ‘Lidal’) was studied in a 2-yr field experiment near Fairbanks, AK. The data were fit to a rectangular hyperbola model. Common lambsquarters densities explained 74 to 75% of the variability in barley yield. The maximum yield loss attributable to common lambsquarters was 23% in 1982 and 36% in 1983.

Leafy spurge causes economic loss by reducing both herbage production and use. Herbage use by grazing cattle in various densities of leafy spurge (Euphorbia esula L. #3 EPHES) was evaluated over a 3-yr period in North Dakota. Forage production and disappearance were estimated in four density classes of leafy spurge. Use of cool- and warm-season graminoids, forbs, and leafy spurge was estimated during the middle and the end of each grazing season. Cattle used 20 and 2% of the herbage in the zero and low density infestations, respectively, by mid-season. Moderate and high density infestations were avoided until the milky latex in leafy spurge disappeared in early fall, and herbage availability in zero and low density infestations declined. Herbage use in moderate and high density infestations increased to an average of 46% by the end of the grazing season compared to 61% in zero and low density infestations. An annual herbage loss of at least 35% occurred in pasture infested with 50% density or more of leafy spurge.

A rotary wiper was developed to apply herbicides selectively to weeds beneath horticultural crops such as fruit trees and ornamentals. Herbicide is delivered internally through a circular pipe manifold imbedded in a rotary polyurethane foam disk, thus avoiding herbicide drift. A free-wheeling bumper wheel, larger than the wiper disk, is mounted just above the disk causing it to move around a tree trunk or shrub on contact. The rotary wiper effectively applied herbicides to weeds within the row of fruit trees.

The objective of this study was to determine the effectiveness of tebuthiuron {N-[5-(1,1-dimethylethyl)- 1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} to treat brush-infested arid rangeland under field-scale conditions. A 130-ha tract in southern New Mexico dominated by creosotebush [Larrea tridentata (Sesse & Moc. ex DC.) Coville #3 LARTR) was treated with pelleted tebuthiuron at 0.4 kg ai/ha. After the fourth season following treatment, control of creosotebush, honey mesquite (Prosopis glandulosa Torr. #PRCJG), and tarbush (Flourensia cernua DC. # FLOCE) was 87, 48, and 100%, respectively. Total shrub density was reduced from 4440 plants/ha to 570 plants/ha. Grass basal area increased from 1.1 to 3.4%. The treatment did not affect forbs greatly. Total herbaceous above-ground biomass production in the fourth season after treatment was 860 kg/ha compared to 140 kg/ha on an adjacent untreated area. Perennial grass production was nearly 11-fold greater on the treated area than on the untreated area.

Effects of 0.1 M ammonium sulfate, 0.1 M potassium phosphate, and 7 g/ha of the isopropylamine salt of imazapyr {(+)-2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-pyridinecarboxylic acid} were evaluated on the phytotoxicity of the ammonium salt of imazaquin {2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-quinolinecarboxylic acid} and the ammonium salt of imazethapyr {(+)-2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-5-ethyl-3-pyridinecarboxylic acid} applied postemergence to pitted morningglory (Ipomoea lacunosa L. #3 IPOLA). While each of these salts and imazapyr applied alone had no effect, combining them with imazaquin or imazethapyr significantly increased control of pitted morningglory.

Since the late 1970s, the reason(s) for the performance of certain pesticides to fail after several years of continuous use has been studied. These pesticides include representatives from the herbicide, insecticide, and fungicide groups, encompassing several classes of chemistry–carbamates, carbamothioates (thiocarbamates), and organophosphates.

Accelerated biodegradation of herbicides in soils can be demonstrated in the laboratory either by treating soil samples with a herbicide under conditions favorable for microbial growth or by sampling field soils soon after herbicidal treatment. Quantitative measurement of accelerated degradation of thiocarbamates in field soils is complicated by the difficulty both of obtaining a proper untreated soil and of obtaining a representative sample by proper mixing of treated soil. Both bacteria and fungi degrade thiocarbamate herbicides, and examples of either class of organisms can be isolated by suitable selection and enrichment conditions. The enzymes involved in the initial steps of thiocarbamate biodegradation seem labile and have not been characterized. Studies of accelerated biodegradation of pesticides should measure the disappearance of the parent or active herbicide using chemical analyses or bioassays. Measuring accelerated biodegradation by determining metabolites (including CO2) is complicated by potential formation of other products, by incorporation of radioactivity into soil microflora, and by complex kinetics partly due to co-metabolism of the herbicide. Additional index words: EPTC, butylate.

Research conducted since 1979 in the north central United States and southern Canada demonstrated that after repeated annual applications of the same thiocarbamate herbicide to the same field, control of some difficult-to-control weed species was reduced. Laboratory studies of herbicide degradation in soils from these fields indicated that these performance failures were due to more rapid or “enhanced” biodegradation of the thiocarbamate herbicides after repeated use with a shorter period during which effective herbicide levels remained in the soils. Weeds such as wild proso millet [Panicum miliaceum L. spp. ruderale (Kitagawa) Tzevelev. #3 PANMI] and shattercane [Sorghum bicolor (L.) Moench. # SORVU] which germinate over long time periods were most likely to escape these herbicides after repeated use. Adding dietholate (O,O-diethyl O-phenyl phosphorothioate) to EPTC (S-ethyl dipropyl carbamothioate) reduced problems caused by enhanced EPTC biodegradation in soils treated previously with EPTC alone but not in soils previously treated with EPTC plus dietholate. While previous use of other thiocarbamate herbicides frequently enhanced biodegradation of EPTC or butylate [S-ethyl bis(2-methylpropyl)carbamothioate], previous use of other classes of herbicides or the insecticide carbofuran (2,3 -dihydro-2,2 -dimethyl-7-benzofuranyl methylcarbamate) did not. Enhanced biodegradation of herbicides other than the thiocarbamates was not observed.

The influence of previous herbicide applications on the degradation rate of butylate [S-ethyl bis (2-methylpropyl)carbamothioate], EPTC (S-ethyl dipropyl carbamothioate), alachlor [2-chloro-N-(2,6-diethyl-phenyl)-N-(methoxymethyl)acetamide], and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] was measured. Degradation studies were conducted on soils with zero to eight previous applications of butylate, zero and six consecutive annual applications of alachlor, and zero to seven previous applications of metolachlor. Previous applications of alachlor or of metolachlor did not affect the rate of degradation when the same herbicide was reapplied. Soils with previous butylate-use history had more rapid degradation of butylate or EPTC than soils with no previous butylate applications. Because soil sterilization reduced 14CO2 evolution to a low level, soil microorganisms could be the primary mechanism of butylate degradation. There was no difference between butylate or EPTC degradation rate in soils treated previously with butylate. Butylate could not be detected 28 days after treatment in soils previously treated with butylate, whereas soils not previously treated with butylate still contained biologically active butylate. Dietholate (O,O-diethyl O-phenyl phosphorothioate) added to butylate generally reduced the rate of butylate degradation in soils previously treated with butylate, but the butylate concentration always was lower in soils treated previously with butylate than in soils without previous butylate applications. Weed control in the field showed rapid loss of butylate and EPTC in soils with previous butylate treatment and that dietholate reduced the rate of butylate and EPTC degradation.

Although the word “xanthium” may conjure up visions of the exotic Far East, it is the generic name of spiny cocklebur (Xanthium spinosum L. #3 XANSP) and common cocklebur (X. strumarium L. # XANST). A familiar weed of fields and roadsides, cocklebur may have originated in the Mediterranean region and has plagued farmers and shepherds since Biblical times. Common cocklebur was considered a beneficient herb in ancient times. Its roots, seeds, and leaves were used as a diuretic and as a tonic to purify the blood. North American Indians used the leaves of spiny cocklebur to counteract hydrophobia.