Methyl isothiocyanate (MIT) consistently killed large crabgrass [Digitaria sanguinalis (L.) Scop. # DIGSA] seed at concentations of 4.0 mM or greater. Concentrations of 0.6 to 1.0 mM MIT delayed germination of large crabgrass seed but ultimately allowed the majority of seed to germinate. Dormant large crabgrass seed were killed at concentrations of MIT similar to those required to kill nondormant seed. MIT stimulated germination of dormant large crabgrass seed at sublethal concentrations (0.1 to 1.0 mM). Experiments with metham (sodium methyldithiocarbamate) in the greenhouse and field (metham rapidly degrades to MIT in soils) confirmed results of laboratory experiments with MIT.

In greenhouse studies, the butyl ester of fluazifop {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy]propanoic acid} applied preemergence at 0.035 kg ai/ha gave 91% control of goosegrass (Eleusine indica Gaertn. ♯ ELEIN), 79% control of large crabgrass [Digitaria sanguinalis (L.) Scop. ♯ DIGSA], and 73% control of giant foxtail (Setaria faberi Herrm. ♯ SETFA). In field studies, the butyl ester of fluazifop at 0.56 kg ai/ha applied preemergence gave 79% control of goosegrass, 76% control of large crabgrass, and 53% control of giant foxtail. The butyl ester of fluazifop at 0.07 kg/ha gave 79 to 85% control of each grass at the pretillering stage in field studies. The same rate applied at the early tillering stage gave 84% control of goosegrass but only 53 and 58% control of large crabgrass and giant foxtail, respectively. Relative species response was similar from spray and leaf-spot applications of the herbicide. The butyl ester of fluazifop at 4 μg/plant when spot-applied to leaves of the three grasses at the tillering stage resulted in 65% control of goosegrass but only 20 and 25% control of large crabgrass and giant foxtail, respectively.

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.

Field experiments in 1984 and 1985 near Headland, AL involved the influence of 18 integrated weed management systems incorporated from nine herbicide-tillage systems (H-T) and two row patterns on control of large crabgrass and Texas panicum, crop yield, and net returns in grain sorghum. The conventional-tillage system plus herbicide combinations; alachlor preplant incorporated (PPI), atrazine postemergence (POST), and paraquat POST directed, provided 90% or greater control of large crabgrass throughout the season and high sorghum yields in one of two years; and 90% or greater control of Texas panicum from mid-June through mid-August and high sorghum yields in both years. Results in 1984 and 1985 similar to those above were obtained with strip tillage plus herbicide combinations; alachlor PPI, atrazine POST, and paraquat POST directed; alachlor PPI and tridiphane plus atrazine POST; and tridiphane plus atrazine POST and paraquat POST directed. Row patterns did not consistently influence control of large crabgrass, Texas panicum, or sorghum yield. Economic net returns ranged from – $20 to $210 per hectare for the large crabgrass control systems in 1984; however, low sorghum yields in 1985 resulted largely in negative returns. Similar net returns were obtained in the Texas panicum experiment.

The relative sensitivity of various crops and weeds to celery root residue incorporated into soil was determined in greenhouse experiments. A range of concentrations was used to determine the percentage of celery residue needed to cause a 50% reduction in plant growth (I50). The most sensitive weed was spiny amaranth and the least sensitive was common purslane. The most sensitive crop was radish and the least sensitive was celery. Selectivity was calculated as crop I50/weed I50 and varied from a maximum of 13 for celery and spiny amaranth to a low of 0.4 for radish and common purslane. Selective weed suppression might be obtained when celery residue is present.

The effects of sethoxydim {2-[1-(ethoxyimino) butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexene-1-one} rate, order, and timing of sequential herbicide applications, and the addition of oil concentrate on sethoxydimbentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H-one 2,2-dioxide] antagonism were studied on broadleaf signalgrass [Brachiaria platyphylla (Griseb.) Nash. ♯3 BRAPP], fall panicum (Panicum dichotomiflorum Michx. ♯ PANDI), and large crabgrass [Digitaria sanguinalis (L.) Scop. ♯ DIGSA] in field experiments during 1980 and 1981. Tank-mixing bentazon with sethoxydim reduced control of these species compared to applications of sethoxydim alone. Sequential applications of the herbicides prevented the antagonism. Variations in time between and order of sequential applications had no consistent effect on efficacy. Increases in sethoxydim rate reduced the severity of the antagonism in some cases, while the addition of oil concentrate had no effect.

Research was conducted in central Georgia to determine the influence of norflurazon on bermudagrass stand and production when applied to newly sprigged bermudagrass and in the spring to dormant bermudagrass. Norflurazon at rates up to 1.12 kg ai/ha on newly sprigged bermudagrass caused moderate chlorosis to the emerging leaves but did not adversely influence stand density or ground cover at 60 and 90 days after treatment (DAT). Norflurazon applied to dormant bermudagrass the spring of 1993 resulted in greater than 50% foliage chlorosis at rates ≥ 1.68 kg/ha. Foliage chlorosis was 94% on bermudagrass treated with 3.36 kg/ha 30 DAT and at spring growth initiation. However, chlorosis level was reduced when bermudagrass began rapid growth. Forage production was not influenced by the early season chlorosis when compared to nontreated areas or areas treated with diuron at 1.12 kg/ha and the weed free check.

Greenhouse studies were conducted to determine host status of weed species for Rhizoctonia solani AG-1, which causes Rhizoctonia foliar blight of soybean. Weed species were barnyardgrass, broadleaf signalgrass, common cocklebur, entireleaf morningglory, hemp sesbania, itchgrass, johnsongrass, large crabgrass, northern jointvetch, prickly sida, purple nutsedge, redweed, sicklepod, and smooth pigweed. Seedling weeds were inoculated with suspensions containing intraspecific group IA and IB isolates of the fungus. In the first study, sclerotia of IA were recovered from tissue of all weeds except smooth pigweed, and mycelia of IA were recovered from all except smooth pigweed and redweed. In that study, neither microsclerotia nor mycelia of IB were recovered from sicklepod, barnyardgrass, or large crabgrass, and only microsclerotia were recovered from itchgrass and purple nutsedge. In the second study, sclerotia of IA, microsclerotia of IB, and mycelia of each isolate were recovered from all weed species. In other studies, R. solani spread from at least six of seven weed species to a noninfected soybean plant growing in close proximity. These studies emphasize the importance of weed control, not only for reducing plant competition and increasing yield, but also for the potential impact on development of RFB.

Large crabgrass [Digitaria sanguinalis (L.) Scop. # DIGSA] control with BAS 9052 OH {2-[1-(ethoxyimino)-butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexene-1-one} was similar whether applied alone or in combination with acifluorfen {5-[2-chloro-4-(trifluoromethyl) phenoxy]-2-nitrobenzoic acid}. Combinations of BAS 9052 OH and bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4-(3H)-one 2,2-dioxide] gave decreased grass control compared to BAS 9052 OH alone. This antagonism between BAS 9052 OH and bentazon was eliminated by applying bentazon as a separate application 1.5 h or longer before the application of BAS 9052 OH. A 0.2 h interval between applications of the herbicides decreased large crabgrass control compared to control obtained with BAS 9052 OH applied alone, but the decrease was signifciantly less than occurred with a concurrent application of the two herbicides.

Experiments were conducted in 1991 and 1992 to evaluate annual grass and broadleaf weed control with bromoxynil applied alone and with graminicides. Bromoxynil controlled velvetleaf better than entireleaf morningglory and controlled both species better than sicklepod. Mixing bromoxynil with fluazifop-P, quizalofop-P, and sethoxydim reduced control of barnyardgrass, green foxtail, large crabgrass, and shattercane. Control of broadleaf signalgrass with quizalofop-P was reduced by bromoxynil. Annual grass control with clethodim was not affected by bromoxynil.

One and two postemergence (POE) applications of the butyl ester of fluazifop {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl] oxy]phenoxy] propanoic acid} or sethoxydim (2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} following preemergence (PRE) application of fluometuron {N,N-dimethyl-N′-[3-(trifluoromethyl)phenyl] urea} were compared to a preplant-incorporated (PPI) application of trifluralin [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine] or pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine] plus fluometuron PRE or pendimethalin plus fluometuron PRE for annual grass control in cotton (Gossypium hirsutum L.) and net economic return to land, overhead, and management. One POE application of either fluazifop or sethoxydim following fluometuron PRE resulted in greater control of a high population of broadleaf signalgrass [Brachiaria platyphylla (Griseb.) Nash. # BRAPP] and greater yield and net return than a PPI application of trifluralin or pendimethalin plus fluometuron PRE. A second application of fluazifop or sethoxydim increased late-season control but did not increase yield or net return. In a high population of large crabgrass (Digitaria sanguinalis L. # DIGSA), fluometuron PRE plus two POE applications of fluazifop or sethoxydim resulted in grass control, lint yield, and net return similar to trifluralin or pendimethalin PPI plus fluometuron PRE. No differences in grass control, crop response, or net return were noted between PPI application of trifluralin or pendimethalin. Control of broadleaf signalgrass and large crabgrass with pendimethalin plus fluometuron PRE was less than with pendimethalin PPI plus fluometuron PRE. In fields with a low population of large crabgrass, fall panicum (Panicum dichotomiflorum Michx. # PANDI), and goosegrass [Eleusine indica (L.) Gaertn. # ELEIN], fluometuron PRE provided excellent season-long control. No benefits were obtained from addition of a grass herbicide. No treatments affected cotton maturity or fiber quality.

Greenhouse and laboratory studies were conducted to determine the effect of 22 postemergence corn broadleaf herbicide combinations on the efficacy of sethoxydim applied to giant foxtail, large crabgrass, and shattercane. Eighteen combinations caused a reduction in sethoxydim efficacy on at least one grass species. Dicamba, atrazine plus dicamba, atrazine plus bentazon, bromoxynil, primisulfuron, CGA-152005 plus primisulfuron, MON 12000, and flumetsulam plus clopyralid plus 2,4-D (NAF-73) were evaluated further on the efficacy and foliar absorption of sethoxydim applied to giant foxtail, large crabgrass, and shattercane. In timing studies, applying all herbicide combinations at 7 or 3 d before sethoxydim application eliminated significant antagonistic interactions. However, applying NAF-73, primisulfuron, or CGA-152005 plus primisulfuron 1 d prior resulted in a reduction in sethoxydim efficacy on at least one grass species. Dicamba, atrazine plus dicamba, and atrazine plus bentazon decreased 14C-sethoxydim absorption 9 to 63% across grass species. Replacing crop oil concentrate (COC) with DASH increased sethoxydim absorption when applied with these herbicides but not to the full extent of sethoxydim applied alone with DASH. Sethoxydim efficacy was retained or improved with DASH when applied with dicamba, atrazine plus dicamba, atrazine plus bentazon, or bromoxynil. When primisulfuron, CGA-152005 plus primisulfuron, MON 12000, or NAF-73 was applied with 14C-sethoxydim no effect on sethoxydim absorption was observed. DASH was less effective than COC at restoring sethoxydim efficacy when applied with these herbicides.

Greenhouse and laboratory studies were conducted to determine the effects of tank-mixing the sodium salt of dicamba (Na-dicamba) with imazethapyr on the efficacy and foliar absorption of imazethapyr, applied with non-ionic surfactant (NIS) or methylated seed oil (MSO), by shattercane, giant foxtail, and large crabgrass. The effects of various salt formulations of dicamba and the addition of ammonium sulfate on efficacy, 14C-absorption and on foliar spray retention by the same species were also evaluated. Na-dicamba antagonized imazethapyr efficacy by reducing 14C-absorption. Using MSO instead of NIS prevented antagonism when Na-dicamba was applied at 70 and 140 g/ha and reduced the severity of the antagonism at greater application rates by greatly increasing 14C-absorption compared to NIS. Reductions in 14C-absorption and spray retention were due to the salt formulations of dicamba rather than the parent acid. The addition of ammonium sulfate prevented dicamba antagonism of imazethapyr toxicity to grassy weeds by maintaining 14C foliar absorption and spray retention at normal levels.

Tomatoes (Lycopersicon esculentum ‘Roma VF’) and four weeds were grown in various combinations in field plots in 1973 and 1974. Season-long interference by jimsonweed (Datura stramonium L.), tall morningglory [Ipomoea purpurea (L.) Roth], and common cocklebur (Xanthium pensylvanicum Wallr.) at densities of 11, 43, and 86/m2 reduced tomato yields in 1973. In 1974, tomato yields were reduced by these three broadleaf weeds at densities of 2.7, 5.4, 8.1, and 11/m2. Season-long interference by large crabgrass [Digitaria sanguinalis (L.) Scop.] reduced tomato yield at densities of 55, 215, and 430/m2 in 1973 and 11, 22, 33, and 55/m2 in 1974. The fresh weight of tomato shoots decreased with all weed densities in both years. Total weed shoot weight increased with density and individual weed weights decreased with increasing densities. Tomato fruit quality, as measured by soluble solids, acidity, and color, was not influenced by the various weeds and densities.

A 3-yr study was initiated in 1982 to determine the effects of herbicides and crop rotations on large crabgrass [Digitaria sanguinalis (L.) Scop. # DIGSA] and broadleaf signalgrass [Brachiaria platyphylla (Griseb.) Nash # BRAPP] population dynamics. Regardless of the crop rotation sequence, broadleaf signalgrass immediately became the predominant weed where standard herbicide programs were used. Large crabgrass became the predominant species after two growing seasons if no herbicides were applied. Domination by large crabgrass appeared to be due to greater seed production. The domination by broadleaf signalgrass in plots treated with herbicides was attributed to its tolerance to the primary grass herbicide alachlor [2-chloro-N-(2,6-diethylphenyl)-N-methoxymethyl)acetamide]. Broadleaf signalgrass emergence from soil treated with 2.2 kg ai/ha was not statistically different from that in untreated soil, while large crabgrass and fall panicum [Panicum dichotomiflorum (L.) Michx. # PANDI] emergence was significantly reduced at the same rate.

Field studies were conducted in 1992 and 1993 to evaluate AC 263,222 applied postemergence (POST) alone and as a mixture with atrazine or bentazon for weed control in imidazolinone-resistant corn. Nicosulfuron alone and nicosulfuron plus atrazine were also evaluated. Herbicide treatments were applied following surface-banded applications of two insecticides, carbofuran or terbufos at planting. Crop sensitivity to POST herbicides, corn yield, and weed control was not affected by insecticide treatments. AC 263,222 at 36 and 72 g ai/ha controlled rhizomatous johnsongrass 88 and 99%, respectively, which was equivalent to nicosulfuron applied alone or with atrazine. AC 263,222 at 72 g/ha controlled large crabgrass 99% and redroot pigweed 100%, and this level of control exceeded that obtained with nicosulfuron alone. AC 263,222 at 72 g/ha controlled sicklepod and morningglory species 99 and 98%, respectively. Nicosulfuron alone or with atrazine controlled these two species less than AC 263,222 at 72 g/ha. Addition of bentazon or atrazine to AC 263,222 did not improve control of any species compared with the higher rate of AC 263,222 at 72 g/ha applied alone. Corn yield increased over the untreated control when POST herbicide(s) were applied, but there were no differences in yield among herbicide treatments.

Fluazifop-P, sethoxydim, and quizalofop were evaluated over two years for postemergence annual grass control in sweet potatoes. All treatments controlled broadleaf signalgrass and large crabgrass, but in 1987 only rates of at least 0.14 kg/ha of fluazifop-P and quizalofop and 0.28 kg/ha of sethoxydim controlled large crabgrass. No. 1 grade and total yield were greater from plots treated with herbicides compared with the weedy check in 1986. In 1987, No. 1 grade and total yield were greater in plots treated with fluazifop-P at 0.14 kg/ha or higher and sethoxydim or quizalofop at 0.28 kg/ha or higher.

Sweet corn was grown with a living mulch of white clover, a dead mulch of rye, and without mulch, in both till and no-till conditions. Unplanted controls were also included in the experimental design. Corn yields were highest in clover treatments early in the experiment but lowest in later years. The declining yields in the clover living mulch were related to the strip application of glyphosate which allowed establishment of perennial and biennial weeds, notably dandelion and horseweed. These overwintering weeds apparently prevented effective control of summer annuals, especially redroot pigweed, common lambsquarters and large crabgrass, by atrazine and metolachlor. Presence of a rye mulch decreased weed biomass and had no detrimental effect on corn yield. In general, corn yield was not affected by tillage, although the number of marketable ears was reduced in the no-till treatments during the drought year of 1988. The much greater weed biomass in the unplanted control treatments showed the importance of crop competition for weed control in sweet corn cropping systems.

Field experiments were conducted to determine effects of adding 2.8 kg/ha (NH4)2SO4 and/or substituting BCH 81508 S for crop oil with sethoxydim applied to large crabgrass, corn, johnsongrass, and common bermudagrass. Adding (NH4)2SO4 did not affect control of johnsongrass or common bermudagrass but did increase control of large crabgrass and corn by 6 and 15%, respectively. Cora control was enhanced more by (NH4)2SO4 at lower sethoxydim rates. Substituting BCH 81508 S for crop oil increased seedling johnsongrass, large crabgrass, common bermudagrass, rhizome johnsongrass, and corn control by 7, 9, 9, 10, and 15%, respectively. A sethoxydim rate by spray adjuvant interaction was observed with seedling johnsongrass, common bermudagrass, and corn where response to BCH 81508 S decreased as sethoxydim rates increased. The effects of substituting BCH 81508 S for crop oil and adding (NH4)2SO4 were independent.

Field experiments were conducted to determine the effects of various densities of four fall-seeded small grain mulches and diphenamid (N,N-dimethyl-α-phenyl benzeneacetamide) on weed control, yield, and quality in no-till flue-cured tobacco (Nicotiana tabacum L. ‘McNair 944’). A greenhouse study investigated the effects of non-soil-incorporated mulch from the same small grains plus alfalfa (Medicago sativa L.) on various growth parameters of tobacco (‘Speight G-70’). None of the mulches used in the greenhouse study adversely affected growth of the tobacco. Mulch from rye (Secale cereale L. ‘Abruzzi’) killed about 2 weeks before transplanting plus diphenamid provided better annual broadleaf weed control (85%) than wheat (Triticum aestivum L. ‘McNair’), barley (Hordeum vulgare L. ‘Keowee’), and no mulch. Oat (Avena sativa L. ‘Brooks’) mulch resulted in 80% broadleaf weed control. There were no differences in annual grass control (which was short lived) among mulches but control was lower in the no-mulch treatment. Rye mulch resulted in a 22% increase in the control of broadleaf weeds compared to no-mulch. Yield of the no-till tobacco did not differ among mulches and averaged 82% of that conventionally grown. The quality was not affected. The rye mulch did not affect the yield or quality of tobacco when compared to a nonmulch, noncultivated treatment. The 18% decrease in the no-till yield was apparently the result of the lack of tillage and increased weed interference and was not due to adverse effects from the rye.