Of 17 thiocarbamate herbicides tested in the greenhouse in repeat soil applications made 4 to 16 weeks apart, 9 showed definite losses in herbicidal activity after the second application. Those showing reduced activity included EPTC (S-ethyl dipropylthiocarbamate), vernolate (S-propyl dipropylthiocarbamate), and butylate (S-ethyl diisobutylthiocarbamate), which have been reported previously to develop accelerated breakdown, plus R-15574 (S-benzyl dipropylthiocarbamate and the sulfoxides of EPTC, vernolate, butylate, SC-7829 (S-propyl diisobutylthiocarbamate), and SC-8149 (S-butyl diisobutylthiocarbamate). Thiocarbamates that showed no significant reduction in activity after the second application were pebulate (S-propyl butylethylthiocarbamate), cycloate (S-ethyl N-ethylthiocyclohexanecarbamate), molinate (S-ethyl hexahydro-1H-azepine-1-carbothioate), R-1880 (S-ethyl dibutylthiocarbamate), R-1856 (S-tertiarybutyl dipropylthiocarbamate), R-1853 (S-isobutyl diethylthiocarbamate), R-1906 (S-butyl diisopropylthiocarbamate), and R-12001 [S-isopropyl 1-(5-ethyl-2-methyl)piperidine carbothioate]. Of 16 nonthiocarbamate herbicides tested, a reduction in control of weeds occurred after the second soil application with 2,4-D [(2,4-dichlorophenoxy)acetic acid], dalapon (2,2-dichloropropionic acid), chlorpropham (isopropyl m-chlorocarbanilate), propham (isopropyl carbanilate), TCA (trichloroacetic acid), pronamide [3,5-dichloro (N-1,1-dimethyl-2-propynyl)benzamide], napropamide [2-(α-naphthoxy)-N,N-diethylpropionamide], bensulide [O,O-diisopropyl phosphorodithioate S-ester with N-(2-mercaptoethyl)benzenesulfonamide], alachlor [2-chloro-2’,6’-diethyl-N-(methoxymethyl)acetanilide], and diethatyl [N-(chloroacetyl)-N-(2,6-diethylphenyl)glycine]. Losses with the latter five herbicides after repeat application have not been reported previously.

The control of western juniper (Juniperus occidentalis Hook.) trees released shrub and herbaceous vegetation from dominance of the tree overstory. Revegetation of the woodland with desirable browse and forage species required weed control of both shrub and herbaceous species. The method of tree control (herbicidal, mechanical, or wood harvesting) influenced subsequent weed control-revegetation options in the understory. Physical restraints imposed by standing dead trees resulting from picloram (4-amino-3,5,6-trichloropicolinic acid) treatment limited the use of weed control and seeding equipment. Accumulation of litter interfered with the use of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] for annual grass control on both the picloram and wood harvest plots. Establishment of forage species was most successful on the mechanically cleared plots. Attempts to revegetate with browse species were largely foiled by native herbivores, and selective predation occurred on herbaceous species.

Field experiments were conducted in 1982 and 1983 on a Dothan sandy loam (Plinthic Paleudult) at Headland, AL, to investigate minimum-tillage production of peanuts (Arachis hypogaea L.). The experiments included two peanut varieties: a) ‘Pronto’ (an earlier maturing Spanish type), and b) ‘Florunner’ (a later maturing runner type). Two row-spacing patterns were used: a) conventional 91-cm rows, and b) a modified twin 18-cm row pattern. A constant seeding rate (140 kg/ha) was used regardless of row spacing. Six herbicide systems were evaluated within each combination of variety and row spacing. The Florunner variety outyielded the Pronto variety across both years and weed management systems. Modified twin 18-cm rows outyielded conventional 91-cm rows across years and peanut varieties. Two of the six weed management systems were successful: 1) paraquat (1,1’-dimethyl-4,4’-bipyridinium ion) + oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide) (preemergence), paraquat (ground cracking), naptalam (N-1-naphthylphthalamic acid) + dinoseb (2-sec-butyl-4,6-dinitrophenol) (postemergence); and 2) paraquat + pendimethalin [N-(1-ethylpropyl-3,4-dimethyl-2,6-dinitrobenzenamine] (preemergence), acetochlor [2-chloro-N(ethoxymethyl)-6’-ethyl-o-acetotoluidide] + dinoseb (ground cracking), and cyanazine {2-[[4-chloro-6-(ethylamino)-s-triazine-2-yl]amino]-2-methylpropionitrile} (early postdirected spray). Both systems provided the best overall control of Texas panicum (Panicum texanum Buckl. ♯ PANTE), Florida beggarweed [Desmodium tortuosum (Sw.) DC. ♯ DEDTO], and sicklepod (Cassia obtusifolia L. ♯ CASOB) and were acceptable for use in minimum-tillage peanut production.

Herbicide treatments containing the butoxyethanol ester of 2,4-D [(2,4-dichlorophenoxy)acetic acid], the dimethylamine salt of dicamba (3,6-dichloro-o-anisic acid), the potassium salt of picloram (4-amino-3,5,6-trichloropicolinic acid), and the isopropylamine salt of glyphosate [N-(phosphonomethyl)glycine] were applied for 6 yr to a pasture in east-central South Dakota containing leafy spurge (Euphorbia esula L. ♯ EPHES). Several treatments resulted in leafy spurge control exceeding 90%. Mean herbage dry-weight yield in treated plots was 2340 kg/ha, a 67% increase over untreated plots. Forage yields did not significantly differ among treatments controlling 90% or more leafy spurge. Marginal net return over marginal cost from herbicide treatments ranged from $35 to –$63/ha. Treatments providing satisfactory leafy spurge control with minimum economic risk were annual spring applications of 2,4-D at 1.7 kg ae/ha or dicamba + 2,4-D at 0.6 + 1.1 kg ae/ha and the biannual application of 2,4-D at 0.8 kg ae/ha.

The addition of chlorflurenol (methyl 2-chloro-9-hydroxyfluorene-9-carboxylate) at 0.6 kg ai/ha or mefluidide {N-[2,4-dimethyl-5-[[(trifluoromethyl)sulfonyl]amino]phenyl] acetamide} at 0.3 kg ai/ha to picloram (4-amino-3,5,6-tricloropicolinic acid) at 0.3 kg ae/ha increased leafy spurge (Euphorbia esula L. # EPHES) control compared to picloram alone. Application of 84 kg/ha nitrogen in the fall prior to a spring treatment of 0.3 kg/ha picloram decreased the original stand (75%) compared to no nitrogen (18%). In greenhouse experiments, chlorflurenol and mefluidide increased the amount of 14C-picloram absorbed approximately twofold when applied in combination but not when applied independently. Based on 14C-picloram absorbed, chlorflurenol and mefluidide each increased the amount of 14C translocated to the root system, whether applied independently or in combination with picloram. An increase in root bud numbers was observed following an application of 0.6 kg/ha chlorflurenol or nitrogen.

Foliage-only, soil-only, and foliage plus soil applications of picloram (4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid), clopyralid (3,6-dichloro-2-pyridinecarboxylic acid), chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl]benzenesulfonamide}, and metsulfuron {2-[[[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl]amino]sulfonyl]benzoic acid} were used to determine the contribution of soil spray deposit to the control of Canada thistle [Cirsium arvense (L.) Scop. ♯ CIRAR] under greenhouse conditions. Herbicide reaching the soil contributed significantly to the suppression of secondary shoot growth, particularly when pots were watered from above. In subirrigated pots, the herbicides showed activity if they were sprayed on moist soil, but not if they were sprayed on dry soil. These results suggest that it is important to shield the soil during postemergence applications of herbicides in greenhouse experiments in order to avoid overestimating foliar activity.

Chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl]benzenesulfonamide} was nontoxic to safflower (Carthamus tinctorius L.) when applied postemergence in 1983 and 1984 at 0.018 and 0.035 kg ai/ha. Trifluralin [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine] at 1.1 and 1.7 kg ai/ha and pronamide [3,5-dichloro(N-1,1-dimethyl-2-propynyl)benzamide] at 0.8 and 1.1 kg ai/ha were applied previously as preplant soil-incorporated treatments. In both years, safflower was relatively free of weeds where trifluralin was applied alone or in sequential treatments with chlorsulfuron. Pronamide, with or without chlorsulfuron, failed to completely control witchgrass (Panicum capillare L. ♯ PANCA) in 1 yr; thus safflower grain yields were reduced 21 to 35% when compared to weed-free safflower. Chlorsulfuron controlled redroot pigweed (Amaranthus retroflexus L. ♯ AMARE), puncturevine (Tribulus terrestris L. ♯ TRBTE), and common sunflower (Helianthus annuus L. ♯ HELAN).

Oxadiazon [2-tert-butyl-4(2,4-dichloro-5-isopropoxyphenyl)-δ2-1,3,4-oxadiazolin-5-one] applied to dormant bermudagrass [Cynodon dactylon (L.) Pers. ‘Tifway’ ♯ CYNDA] retarded early foliar growth more than other herbicides evaluated. When bensulide [O,O-diisopropyl phosphorodithioate S-ester with N-(2-mercaptoethyl)benzenesulfonamide] treatments were delayed until after bermudagrass initiated spring growth, foliar growth and quality were generally lower than when the treatments were applied to dormant turf. Retardation of early foliar bermudagrass growth by 2,4-D [(2,4-dichlorophenoxy)acetic acid] + mecoprop {2-[(4-chloro-o-tolyl)oxy] propionic acid} + dicamba (3,6-dichloro-o-anisic acid) was generally the same whether applied to dormant or semidormant turf. This combination of herbicides reduced the quality and density of bermudagrass when applied to growing but not to dormant turf. Atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] did not retard bermudagrass growth or affect density whether applied to dormant or semidormant turf, but turf quality was slightly lower when atrazine was applied to semidormant turf.

Eight accessions of weedy nightshades representing five species were evaluated for response to four herbicides applied preemergence in growth chamber studies and four herbicides applied postemergence in greenhouse studies. Species differed in susceptibility to all herbicides evaluated. The largest differences were found with postemergence applications of chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl]benzenesulfonamide}; hairy nightshade (Solanum sarrachoides Sendt. ♯ SOLSA) was relatively susceptible, but eastern black nightshade (S. ptycanthum Dun.) was very tolerant. S. ptycanthum, however, was one of the more susceptible species. It was always more susceptible than black nightshade (S. nigrum L. ♯ SOLNI) to all other herbicides evaluated.

Field experiments were conducted to investigate methods of controlling red rice (Oryza sativa L. ♯ ORYSA) in drill-seeded rice (O. sativa). Treatments included the rice cultivar ‘Mars', coated with calcium peroxide (CaO2) at 40% (w/w) and a crop protectant, R-33865 (O,O-diethyl-O-phenyl phosphorothioate) at 0.5 and 1% (v/w). Molinate (S-ethyl hexahydro-1H-azepine-1-carbothioate) at 6.7 kg ai/ha was applied preplant incorporated (ppi). The land was flooded (2.5 to 5 cm deep) after seeding with rice (100 kg/ha, 2.5 cm deep), and the water was maintained throughout the growing season. CaO2, with or without molinate, increased rice grain yield 50% and increased rice culm density fivefold above untreated rice. Molinate applied ppi controlled 96% of the red rice. Rice seed coated with only CaO2 or with CaO2 plus R-33865 at 0.5%, each combined with ppi molinate, produced 5690 and 6030 kg/ha of grain, respectively. These high yields were associated with red rice control by molinate and good stands of rice provided by O2 supplied by CaO2. R-33865 applied to rice seed at 1% (v/w) injured rice by reducing rice culm densities 41%, compared with rice without protectant.

Interference of Powell amaranth (Amaranthus powellii S. Wats. ♯ AMAPO) in sugarbeet (Beta vulgaris L. ‘Mono Hy A4’) was determined in field experiments. Yield of sugarbeet roots and recoverable sucrose/ha decreased as the density of Powell amaranth increased. At densities of 6, 12, 18, and 24 Powell amaranth plants/30 m of row, root yields were reduced 8, 14, 24, and 25%, respectively, and recoverable sucrose yields were reduced 7, 13, 23, and 24%, respectively. The minimum number of Powell amaranth plants required per 30 m of row to reduce sugarbeet root yields was estimated to be nine in 1982 and 11 in 1983.

The relationship between Tartary buckwheat (Fagopyrum tataricum (L.) Gaertn. ♯ FAGTA) plant density (x) and percent yield loss (ŷ) was expressed by the following linear regression equations for barley (Hordeum vulgare L.) and wheat (Triticum aestivum L.), respectively; ŷ = 0.63 + 2.75 √x and ŷ = 5.04 + 3.05 √x. Tartary buckwheat causes serious yield reduction in barley and wheat. A Tartary buckwheat density at 30 plants/m2 at emergence reduced barley yield by 16% and wheat yield by 22%.

Single and sequential applications of mefluidide {N-[2,4-dimethyl-5-[[(trifluoromethyl)sulfonyl] amino] phenyl] acetamide} and acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid} were evaluated in the field for velvetleaf (Abutilon theophrasti Medic. ♯ ABUTH) and common cocklebur (Xanthium pensylvanicum Wallr. ♯ XANPE) control in soybeans [Glycine max (L.) Merr. ‘Williams’]. Acifluorfen was applied at 0.4 or 0.6 kg ai/ha alone or 3, 5, or 7 days following application of 0.1 or 0.3 kg ai/ha mefluidide. Acifluorfen applied alone provided acceptable control of velvetleaf and common cocklebur in the two- and three-leaf stage of growth, but acifluorfen was not as effective when applied to weeds with five to eight true leaves. Sequential applications of mefluidide and acifluorfen often increased velvetleaf and common cocklebur control, compared to either herbicide applied alone.

The effect of rainfall on the performance of a tank mixture of desmedipham [ethyl m-hydroxycarbanilate carbanilate(ester)] and phenmedipham (methyl m-hydroxycarbanilate m-methylcarbanilate) applied postemergence to redroot pigweed (Amaranthus retroflexus L. ♯ AMARE), wild mustard (Sinapsis arvensis L. ♯ SINAR) and sunflower (Helianthus annuus L.) was evaluated in field studies. The occurrence of 1 mm of rain immediately after herbicide application significantly decreased the control of redroot pigweed and wild mustard. A rainfall quantity of 1 mm also reduced injury symptoms on sunflower. Simulating a 12.7-mm rain less than 18 h after desmedipham and phenmedipham application effectively reduced toxicity to redroot pigweed and sunflower. Toxicity to these two species increased at a lesser rate than for wild mustard as the time interval prior to rain was increased. A rain-free period of 6 h was predicted for near-maximum control of wild mustard with these herbicides.

Eleven herbicide systems were evaluated from 1981 to 1983 for cotton (Gossypium hirsutum L. ‘Stoneville 825’) planted no-till directly into cover crops or winter fallow and for cotton planted following conventional tillage. Herbicide systems consisted of paraquat (1,1’-dimethyl-4,4’-bipyridinium ion) or glyphosate [N-(phosphonomethyl)glycine] and/or residual herbicides applied prior to crop emergence. Some systems also included early postemergence or postemergence-directed applications. Cover crops were crimson clover (Trifolium incarnatum L.), hairy vetch (Vicia villosa Roth.), and rye (Secale cereale L.). Soil cover in fallow treatments was comprised mainly of cotton stalk residue. Conventional tillage and seedbed preparation included fall moldboard plowing and spring disking/smoothing. Treatments were maintained in the same site each year. Order of cover crop susceptibility to herbicides applied prior to crop emergence was rye>clover>vetch. In 1981, all residual treatments except cyanazine {2-[[4-chloro-6-(ethylamino)-1,3,5-triazin-2-yl]amino]-2-methylpropanenitrile} alone prior to crop emergence provided better than 80% control of annual weeds. In subsequent years only systems that included applications prior to crop emergence and postemergence-directed herbicides provided acceptable control. From 1981 to 1983, annual grasses increased 20- to 100-fold for systems in which control was poor. Weed control was generally superior in conventional tillage. Vetch adversely affected cotton stands in all 3 yr. Also, in 1982, reduced cotton stands resulted from cyanazine treatments applied prior to crop emergence in clover, vetch, and fallow. Cotton yields were affected by cover dessication, annual weed control, and cotton stands. Buildup of annual weeds reduced yields to near zero for some treatments in 1983.

Terbacil (3-tert-butyl-5-chloro-6-methyluracil), diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea], hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione], and metribuzin [4-amino-6-butyl-3-(methylthio)-as-triazin-5(4H)-one] controlled palmer amaranth (Amaranthus palmeri S. Wats. ♯ AMAPA) in established alfalfa (Medicago sativa L.) when applied after first harvest. However, these same herbicides did not control palmer amaranth when applied early-season in March. Alfalfa forage yields were increased when palmer amaranth was controlled. Residue levels of terbacil and its metabolites in alfalfa forage from plots treated postharvest with 1.1 kg/ha of terbacil were well below the 5-ppm tolerance level established for terbacil in alfalfa. There was some chlorosis of alfalfa foliage following the postharvest use of the 1.1 kg ai/ha of terbacil. There was also a yield reduction of alfalfa in two of the six experiments (one from a March and one from a June application) where 1.1 kg ai/ha of terbacil was evaluated.

The methyl ester of diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid} mixed with soil at 1, 2, and 3 ppmw reduced the growth of Bromus species in the greenhouse as follows: downy brome (Bromus tectorum L. ♯ BROTE) more than Japanese brome (Bromus japonicus Thunb. ex Murr. ♯ BROJA) more than cheat (Bromus secalinus L. ♯ BROSE). The decrease in herbicide effect (decay) over time was described better using a second-order equation than a first-order equation. Plant response-herbicide dose relationships were described best with a cubic polynomial equation.

Glasshouse and growth chamber experiments were conducted to determine chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl] benzenesulfonamide} phytotoxicity to kochia [Kochia scoparia (L.) Schrad. ♯ KCHSC] and green foxtail [Setaria viridis (L.) Beauv. ♯ SETVI] as influenced by temperature and humidity for 1 week after treatment, and by soil moisture and nitrogen. Chlorsulfuron was more phytotoxic to both kochia and green foxtail at 95 to 100% than at 45 to 50% relative humidity for 1 week after treatment whether at 10, 20, or 30 C. Chlorsulfuron phytotoxicity was similar with all posttreatment temperatures at each humidity, except that phytotoxicity was lower at 30 C than at 10 or 20 C at 90 to 100% humidity. Surfactant added to chlorsulfuron exhanced control of kochia more than that of green foxtail and overcame temperature and humidity effects on chlorsulfuron phytotoxicity. A simulated rainfall of 2 mm after chlorsulfuron application reduced toxicity of chlorsulfuron to green foxtail more than to kochia. Chlorsulfuron was more phytotoxic to green foxtail growing with a high than a low soil nitrogen level. High soil moisture following chlorsulfuron application enhanced phytotoxicity to kochia and green foxtail compared to high soil moisture before treatment.