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.

Field research from 1986 to 1988 evaluated control of alfalfa, dandelion, orchardgrass, and annual weeds in corn with sequential herbicide treatments. Glyphosate applied the previous fall controlled 95% or more of the dandelion and orchardgrass before postemergence treatments. Atrazine applied early preplant or with paraquat the day before planting only partially controlled the perennial species. Atrazine applied postemergence usually controlled vegetation escaping initial treatment except orchardgrass following the atrazine treatments. Adding tridiphane increased weed control with atrazine or cyanazine applied postemergence only when fall panicum was present. Herbicides applied postemergence increased corn yield compared to the initial treatments alone, and few differences among postemergence treatments were observed. Sequential treatments which included glyphosate applied in the fall controlled 82% or more of each perennial species before the next growing season. Orchardgrass control was 81% or less the following spring when the initial treatment was atrazine or atrazine plus paraquat.

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.

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.

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.

The efficacies of microencapsulated (ME) and emulsifiable concentrate (EC) formulations of 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 compared in petri dish and soil bioassays. At equimolar concentrations, EC-alachlor inhibited shoot growth of barnyardgrass [Echinochloa crus-galli (L.) Beauv. # ECHCG], large crabgrass [Digitaria sanguinalis (L.) Scop. # DIGSA], and fall panicum (Panicum dichotomiflorum Michx. # PANDI) more than ME-alachlor. ME- and EC-metolachlor caused similar effects on the three grass weeds tested. ME- and EC-alachlor in combination caused effects on barnyardgrass shoot growth intermediate to results with either formulation alone. Air-drying and remoistening of alachlor-treated filter paper or soil before sowing barnyardgrass or fall panicum caused greater shoot length and fresh weight reduction than ME-alachlor that was not dried.

Thiazopyr at 0.14, 0.28, and 0.42 kg ai/ha and pendimethalin at 1.1 kg ai/ha applied preemergence (PRE) were compared as components in weed management systems for no-till cotton. Mid- and late-season control of mixtures of large crabgrass, goosegrass, and fall panicum by thiazopyr at 0.28 kg/ha was 89 to 97% and 11 to 50%, respectively, compared with 11 to 38% midseason and 0 to 5% late-season control by pendimethalin. Thiazopyr at 0.42 kg/ha and pendimethalin controlled broadleaf signalgrass 44 and 0%, respectively, late in the season. Adding fluometuron PRE at 1.7 kg ai/ha had little to no effect on large crabgrass, goosegrass, and fall panicum control but increased broadleaf signalgrass control 47 to 79 percentage points compared with thiazopyr or pendimethalin alone. Late-season control of annual grasses by thiazopyr or pendimethalin plus fluometuron PRE followed by methazole plus MSMA early postemergence (POST)-directed and cyanazine plus MSMA late POST-directed was at least 95% at two locations and 80% at the third location. Common lambsquarters was controlled 54 and 95% in systems without and with fluometuron PRE, respectively. Acceptable control of ivyleaf, pitted, and tall morningglories at all locations and smooth pigweed at two of three locations was achieved only in systems with POST-directed herbicides. Adding POST-directed herbicides to systems with thiazopyr or pendimethalin plus fluometuron PRE increased cotton yield at two of three locations. Treatments had no effect on fiber quality.

Consecutive annual applications of 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 made to continuous no-till corn (Zea mays L. ‘Pioneer 3184’ in 1982 and 1983, ‘Pioneer 3744’ in 1984, and ‘Pioneer 3378’ in 1985 to 1987). In a 5-yr study, control of the dominant annual grass species, large crabgrass [Digitaria sanguinalis (L.) Scop. # DIGSA], by alachlor declined to less than 50% by the fifth year. Control of large crabgrass by metolachlor remained greater than 80% throughout the study but metolachlor allowed the establishment of a greater fall panicum (Panicum dichotomiflorum Michx. # PANDI) population in this and an additional 3-yr study than in chloroacetamide-free checks. In the 3-yr study in which giant foxtail (Setaria faberi Herrm. # SETFA) was dominant, annual applications of metolachlor and a microencapsulated formulation of alachlor provided better control in the second year than the emulsifiable concentrate formulation of alachlor, but formulation differences diminished in the third year.

An experiment was initiated in 1970 and continued through 1979 by exhuming and germinating seed of 12 economic weed species buried beneath 23 cm of soil in eastern and western Nebraska. Loss in germination of exhumed seeds over years is mathematically characterized by the formula for the rectangular hyperbola, which represents many shapes of curves that have zero as their lower limit. Of the 12 weed species, only fall panicum (Panicum dichotomiflorum Michx.) and redroot pigweed (Amaranthus retroflexus L.) seed germination did not drop significantly over the 10-yr burial period. Germination of redroot pigweed seed was higher when buried in eastern Nebraska, but was higher for smooth groundcherry (Physalis subglabrata Mack&Bush.) and velvetleaf (Abutilon theophrasti Medic.) when buried in western Nebraska. Germination of the other nine species were not affected by burial location. The 12 weed species can be ranked as those showing most to least rapid loss of germination during burial for 10 yr as follows: honeyvine milkweed [Ampelamus albidus (Nutt.) Britt.], hemp dogbane (Apocynum cannabinum L.), kochia [Kochia scoparia (L.) Schrad.], sunflower (Helianthus annum L.), large crabgrass [Digitaria sanguinalis (L.) Scop.], common milkweed (Asclepias syriaca L.), musk thistle (Carduus nutans L.), velvetleaf, fall panicum, redroot pigweed, green foxtail [Setaria viridis (L.) Beauv.], and smooth groundcherry.

Field experiments were conducted in 1994 and 1995 to evaluate weed control in imidazolinone-resistant corn with postemergence applications of imidazolinone and sulfonylurea herbicides. Imazethapyr controlled 100% of redroot pigweed, jimsonweed, and eastern black nightshade. Control of fall panicum with imazethapyr was inconsistent, with control ranging from 42 to 85%. Imazethapyr provided less than 55% control of common lambsquarters and 43% of large crabgrass. Imazethapyr plus either atrazine, 2,4-D, or dicamba increased control of common lambsquarters compared to imazethapyr alone. Fall panicum control was > 95% with nicosufluron. CGA-152005 and MON 12000 did not control eastern black nightshade. In 1995, corn yield was greater with the hand-weeded check compared to all herbicide treatments. The greatest return over herbicide cost with imazethapyr was obtained with imazethapyr plus atrazine. Nicosulfuron plus CGA-152005 provided the greatest return over herbicide cost when averaged across years.

Formulated and technical grade HOE-39866 [ammonium-(3-amino-3-carboxypropyl) methylphosphinate] at concentrations of 10–1, 10–2, and 10–3M were applied to leaf blade tissues of nonreproductive adult redroot pigweed (Amaranthus retroflexus L. # AMARE) and fall panicum (Panicum dichotomiflorum Michx. # PANDI). Tissues were sampled at regular intervals after treatment and prepared for light microscopic examination. The major response of both species involved rupture and contortion of the interveinal mesophyll cells with concomitant disorganization of the bundle sheath cells. Rapid epidermal collapse occurred in redroot pigweed but not in fall panicum. The absence of adjuvants resulted in nonuniform symptom expression as herbicide droplets accumulated in depressions and along leaf margins. No other adjuvant-specific effect was observed. Herbicide concentration did not alter the final response but the time-to-expression increased as concentration decreased.

Field experiments conducted in 1988 and 1989 evaluated clomazone alone and in a systems approach for weed control in peanut. Clomazone PPI at 0.8 kg ai/ha controlled common ragweed, prickly sida, spurred anoda, and tropic croton better than ethalfluralin and/or metolachlor applied PPI. POST application of acifluorfen plus bentazon was not needed to control these weeds when clomazone was used. Acifluorfen plus bentazon improved control of these weeds when clomazone was not used and generally were necessary to obtain peanut yields regardless of the soil-applied herbicides. Alachlor PRE did not improve clomazone control of any weed species evaluated. Fall panicum and large crabgrass control was similar with clomazone or clomazone plus ethalfluralin.

Field studies were conducted at Arlington, WI, in 1996 and 1997 and at Georgetown, DE, and LeSueur, MN, in 1997 to determine weed control efficacy, crop injury, and yield response of PAT-transformed sweet corn to glufosinate-based weed management. Sequential applications of glufosinate 10 to 18 d apart at 0.4 and 0.3 kg ai/ha controlled common lambsquarters, common ragweed, velvetleaf, wild-proso millet, and fall panicum 90% or better at all locations. Weed control varied little among 0.3, 0.4, or 0.3 and 0.3 (sequential) kg/ha glufosinate rates. Glufosinate applied alone, with, or following atrazine controlled velvetleaf 90% or greater but was less consistent on common ragweed and common lambsquarters (73 to 100%). Atrazine plus metolachlor applied preemergence (PRE) and glufosinate applied alone postemergence (POST) provided inconsistent wild-proso millet and fall panicum control (43 to 99%). Metolachlor followed by glufosinate improved consistency of grass control (> 76%). Glufosinate followed by cultivation provided 80% or greater control of velvetleaf and wild-proso millet. Glufosinate did not injure or delay maturity of PAT-transformed sweet corn. Sweet corn treated with glufosinate resulted in yields greater than or equal to the sweet corn that was hand-weeded or received a standard herbicide treatment.

In field studies conducted in 1984, 1985, and 1986, annual grass control by a microencapsulated (ME) formulation of alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide] generally was greater than that by the emulsifiable concentrate (EC) in no-till and was comparable to EC-alachlor in conventionally tilled corn (Zea mays L.) and soybeans [Glycine max (L.) Merr.]. In 1986, ME-metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] controlled annual grass similar to EC-metolachlor. In greenhouse studies, shoot height and fresh weight of barnyardgrass [Echinochloa crus-galli (L.) Beauv. # ECHCG] sown in pots and treated with ME-alachlor was significantly greater than that treated with EC-alachlor. Soybean straw on the soil surface did not affect the differences between alachlor formulations in the greenhouse.

Alachlor at 3.4 and 6.7 kg ha-1, metolachlor at 2.8 and 5.6 kg ha-1, and propachlor at 4.5 and 9.0 kg ha-1 were applied to grain sorghum in field experiments conducted in 1981 and 1982. ‘Dekalb E-59’ and ‘Pioneer 8311’ grain sorghum were tested with and without the seed protectants cyometrinil and flurazole in both experiments. ‘Funk's G-1350’ was tested with and without cyometrinil and CGA-92194 in one experiment. Alachlor and metolachlor caused serious injury (stunting and, in some instances, reductions in stand and yield) to grain sorghum without the seed protectants. Less severe injury to grain sorghum occurred with alachlor and metolachlor at high rates even in the presence of the seed protectants. The three seed protectants were equally effective in preventing crop injury. Only minor injury to grain sorghum, with or without the seed protectants, occurred with propachlor at both rates. Overall, early-season weed control was 81 to 100%; however, propachlor at the rates tested was noticeably weaker than alachlor and metolachlor against some annual grasses.

A 3-yr study was conducted to evaluate efficacy and soybean tolerance of cinmethylin. Cinmethylin was applied preemergence alone at 0.6, 0.8, and 1.0 kg ai/ha or in combination with metribuzin at 0.3 kg/ha. These treatments did not injure soybeans in field trials in 1984, 1985, and 1986. The combination of cinmethylin at 0.7 kg/ha and metribuzin at 0.3 kg/ha controlled more than 90% of large crabgrass, fall panicum, and yellow foxtail. Redroot pigweed and common lambsquarters control was also excellent. Residual control of all grass species was excellent for 8 weeks after preemergence application, followed by reduced control in two of the three grasses. The combination of cinmethylin and metribuzin at 0.7 and 0.3 kg/ha, respectively, significantly increased soybean yields compared to those of untreated plots. These yields were comparable with those obtained from the combination of alachlor and metribuzin at 2.0 and 0.3 kg/ha, respectively. Cinmethylin treatments had no adverse effects on soybean yield components including pods/plant, seed/pod, and seed weight. Cinmethylin shows potential as a preemergence herbicide for full-season weed control in soybean production.

Three levels of weed control (0, 70, and 100%) were maintained in 1989 during corn production at two sites. Weed control in 1990 with a premix formulation of metolachlor and atrazine was directly related to 1989 control levels. Herbicides generally were more effective in conventional tillage than in no-tillage. In no-tillage, giant foxtail control in 1990 averaged 59% following 100% control in 1989 compared to 15% following 0% weed control. At one location, tillage minimized the impact of the prior year's weed control with herbicides providing greater than 85% control in conventional tillage regardless of prior history. In no-tillage, weed control of 85% or better was obtained only following 100% control the previous year.

The effect of spray carrier volume on the antagonism of sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} by bentazon [3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] was investigated under greenhouse and field conditions. In the laboratory, the spray droplet overlap between components of a sequential spray application increased from 17 to 50% as carrier volume was increased from 94 to 374 L/ha, respectively. Carrier volume had a significant influence on treatments of sethoxydim alone and sethoxydim sequentially applied with bentazon, but not on the tank mixture of the two herbicides. Carrier volumes of 94 and 187 L/ha used to deliver sethoxydim alone and the sethoxydim/bentazon sequential treatment were superior to the use of 374 L/ha for the control of large crabgrass [Digitaria sanquinalis (L.) Scop. # DIGSA], fall panicum (Panicum dichotomiflorum Michx. # PANDI), and goosegrass (Eleusine indica Gaertn. # ELEIN). There was no difference in grass control between sethoxydim alone and the sequential treatment except at carrier volumes of 187 L/ha or more with which the sequential treatment was less effective. Rates of 0.06 and 0.11 kg ai/ha of sethoxydim were influenced more by changes in carrier volume than 0.22 kg/ha in both the alone and sequential treatments.

Broadleaf signalgrass [Brachiaria platyphylla (Griseb.) Nash # BRAPP has recently become the dominant annual grass in certain fields of the North Carolina Coastal Plains. Previously, fall panicum (Panicum dichotomiflorum Michx. # PANDI) and large crabgrass [Digitaria sanguinalis (L.) Scop. # DIGSA] were the dominant annual grasses in the region. One of the possible reasons for the observed population shift could be production of inhibitors or stimulators by one species that affects the population dynamics of the other species. Studies were initiated to evaluate the effects of broadleaf signalgrass, large crabgrass, and fall panicum residue, applied as a mulch or soil incorporated, on five indicator species: the three weeds themselves, corn (Zea mays L.), and soybean [Glycine max (L.) Merr.]. At expected residue levels, the degree of inhibition or stimulation from fall panicum and broadleaf signalgrass was determined to be significant for some indicator species. When such responses were seen, the amount of residue necessary to produce these results was usually within the concentrations normally observed in field situations. Based on these results, it appears that the observed population shift is partially mediated by the production of inhibitors or stimulators through plant residue. Other factors such as differential herbicide selectivity and crop rotation are being investigated.

Field studies were conducted under full-season conventional tillage in Delaware and New Jersey to determine the critical time to apply glyphosate with or without residual herbicides for optimum weed control in glyphosate-resistant soybean (GRS). The residual herbicides tank-mixed with glyphosate (0.84 kg/ha) were clomazone (0.55 kg/ha) and imazethapyr (0.063 kg/ha). Herbicide application was made at cracking, unifoliate, and one- to six-trifoliate stages of GRS. Weeds varied in growth stages from preemergence (PRE) at cracking to an average height of 30 cm at the six-trifoliate stage of GRS. Herbicide activity varied by year and weed species. Herbicidal action was better under high (>125 mm/mo) than low (<100 mm/mo) rainfall regime. Glyphosate application without residual herbicides was less effective at cracking and unifoliate than at one- to three-trifoliate leaf stages. Mixing residual herbicides with glyphosate at cracking and unifoliate stages enhanced weed control but made no difference when application was delayed until one- to three-trifoliate stages. For optimum weed control in GRS, the window of application for glyphosate alone was between the one- and three-trifoliate leaf stages, approximately 18 to 28 days after planting (DAP). If glyphosate was tank-mixed with residual herbicides, the window of application extended from cracking until the four-trifoliate stage; and weed interference until the four-trifoliate stage (approximately 32 DAP) did not depress GRS yield.