Flumioxazin plus metolachlor mixtures preemergence (PRE) were evaluated with or without postemergence (POST) herbicides for weed control and peanut (Arachis hypogaea) response in three North Carolina studies. Metolachlor PRE at 2.24 kg ai/ha controlled goosegrass (Eleusine indica) and yellow nutsedge (Cyperus esculentus) 93 and 80%, respectively, and control was not improved with flumioxazin or norflurazon. Metolachlor plus flumioxazin PRE at 0.07 or 0.11 kg ai/ha controlled common lambsquarters (Chenopodium album); entireleaf (Ipomoea hederacea var. integriuscula), ivyleaf (I. hederacea), and pitted morningglory (I. lacunosa); and prickly sida (Sida spinosa) better than metolachlor plus norflurazon PRE at 1.34 kg ai/ha. Morningglories (Ipomoea spp.) were controlled 77 and 86% with flumioxazin PRE at 0.07 and 0.11 kg/ha, respectively, and control was increased to nearly 100% with acifluorfen plus 2,4-DB or lactofen plus 2,4-DB POST. Peanut injury by flumioxazin and norflurazon was observed at one location in 1997; however, yields were not reduced. Peanut treated with metolachlor plus flumioxazin PRE at either rate yielded at least 3,750 kg/ha compared to 3,120 kg/ha with metolachlor plus norflurazon PRE or 1,320 kg/ha with metolachlor PRE.

In field studies, mefluidide {N-[2,4-dimethyl-5-[[(trifluoromethyl)sulfonyl] amino] phenyl] acetamide} was most effective as an enhancing agent for bentazon [3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] and/or acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid} when applied as a tank mixture compared to sequential applications. The influence of mefluidide rate on weed control was not consistent. Additives improved the control of several weed species evaluated, but mefluidide generally was only equal to petroleum oil concentrate (phytobland petroleum oil plus emulsifiers in an 83:17 ratio) as an enhancing agent for bentazon and/or acifluorfen.

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.

The influence of temperature and relative humidity on the activity of acifluorfen, fomesafen, lactofen, and acifluorfen plus bentazon on prickly sida, pitted and entireleaf morningglory, and common cocklebur was evaluated in a growth chamber. Reduced control of all species was observed at 50% relative humidity as compared to 85% relative humidity when temperatures were higher (32/55 C day/night). Similar response to relative humidity was observed at the lower temperature (25/15 C) when treatments were applied 14 days after emergence (DAE). Changes in temperature at the same relative humidity did not alter herbicidal activity. Delaying application timing from 7 to 14 DAE decreased control by all herbicides except lactofen applied at high relative humidity, which controlled prickly sida at both 7 and 14 DAE.

The acetolactate synthase-inhibiting herbicides chlorimuron and imazaquin, and the diphenylether herbicides acifluorfen and lactofen, were applied alone and in all possible combinations to the foliage of common cocklebur, pitted morningglory, and prickly sida to evaluate interacting effects on absorption and translocation. The addition of unlabeled acifluorfen to 14C-chlorimuron increased absorption in common cocklebur, pitted morningglory, and prickly sida. Lactofen also increased absorption of 14C-imazaquin in all species. Conversely, imazaquin reduced absorption or translocation of 14C-acifluorfen in common cocklebur or pitted morningglory, respectively. In all species, absorption was lower when unlabeled chlorimuron or imazaquin was combined with 14C-lactofen than when applied alone.

The weed control spectrum of clomazone, the influence of clomazone on the performance of other herbicides, and the performance of tank mixtures containing clomazone were evaluated from 1985 through 1987. Clomazone applied preemergence at 280 g ai/ha controlled 90 to 100% of barnyardgrass, giant foxtail, goosegrass, large crabgrass, seedling johnsongrass, prickly sida, and velvetleaf. Clomazone at reduced rates was more effective applied preemergence than preplant-incorporated for 10 of 23 weed species. Clomazone enhanced imazaquin activity on entireleaf morningglory and sicklepod in 1986. A tank mixture of clomazone, imazaquin, and metribuzin at half the labeled rates reduced soybean injury, increased soybean yield, and controlled weeds as well as the mixture at labeled rates.

Experiments were conducted at three locations in Louisiana from 1992 to 1994 to evaluate broadleaf weed control with sulfentrazone. Sulfentrazone at 0.42 kg ai/ha applied PPI or PRE provided at least 93% control of entireleaf morningglory in all years at all locations, which was greater than control with metribuzin PRE. Prickly sida control with sulfentrazone ranged from 83 to 94%, which was equal to or greater than control with metribuzin. Hemp sesbania and sicklepod control with sulfentrazone was unacceptable (≤75%) regardless of application method and generally was lower than control with metribuzin. Greater than 90% control of smellmelon and hophornbeam copperleaf was observed with all treatments. Minor but transient soybean injury was noted at one location in one year. Soybean yields following sulfentrazone PRE at St. Joseph were greater than yields with metribuzin as a result of the general increase in broadleaf weed control.

Cloransulam-methyl applied postemergence (POST) following various preplant-incorporated (PPI) herbicides was evaluated in four experiments for weed control in North Carolina soybean over a 2-yr period at three locations. Acifluorfen plus bentazon or chlorimuron alone applied POST injured soybean more than cloransulam-methyl when following any soil-applied herbicide. When following trifluralin PPI, cloransulam-methyl controlled common ragweed, entireleaf morningglory, and pitted morningglory comparable to acifluorfen plus bentazon or chlorimuron. Common lambsquarters and prickly sida control was higher when acifluorfen plus bentazon was applied POST following trifluralin PPI compared to trifluralin PPI followed by cloransulam-methyl or chlorimuron. Acifluorfen plus bentazon or chlorimuron POST controlled yellow nutsedge and smooth pigweed more than cloransulam-methyl POST when following trifluralin PPI. When trifluralin was applied PPI in mixtures with chlorimuron plus metribuzin, flumetsulam, or imazaquin, control of most species was similar regardless of POST treatment used. Soybean treated with cloransulam-methyl yielded 250 kg/ha more than treatments with chlorimuron when these herbicides followed trifluralin plus flumetsulam or trifluralin plus imazaquin. Net returns with different herbicide systems followed trends similar to soybean yield.

Field experiments were conducted from 1993 to 1995 to compare weed control by the isopropylamine salt of glyphosate at 0.21, 0.42, 0.63, and 0.84 kg ae/ha applied at three stages of weed growth. Weed control by glyphosate applied at these rates alone or with ammonium sulfate at 2.8 kg/ha was also evaluated. In other experiments, potential interactions between glyphosate and acifluorfen, chlorimuron, and 2,4-DB were evaluated. Velvetleaf, prickly sida, sicklepod, pitted morningglory, entireleaf morningglory, palmleaf morningglory, and hemp sesbania were controlled more easily when weeds had one to three leaves compared with control when weeds had four or more leaves. Glyphosate controlled redroot pigweed, velvetleaf, prickly sida, sicklepod, and barnyardgrass more effectively than pitted morningglory, entireleaf morningglory, palmleaf morningglory, or hemp sesbania. Increasing the rate of glyphosate increased control, especially when glyphosate was applied to larger weeds. Greater variation in control was noted for pitted morningglory, palmleaf morningglory, prickly sida, and velvetleaf than for redroot pigweed, sicklepod, entireleaf morningglory, or hemp sesbania. Ammonium sulfate increased prickly sida and entireleaf morningglory control but did not influence sicklepod, hemp sesbania, or barnyardgrass control. Acifluorfen applied 3 d before glyphosate or in a mixture with glyphosate reduced barnyardgrass control compared with glyphosate applied alone. Chlorimuron did not reduce efficacy. Mixtures of glyphosate and 2,4-DB controlled sicklepod, entireleaf morningglory, and barnyardgrass similar to glyphosate alone.

Field experiments were conducted in 1986, 1987, and 1988 to evaluate imazethapyr rate and time of application on postemergence control of 24 weed species. Contour graphs were developed that predicted imazethapyr rates required for various levels of weed control based upon weed leaf number at application. Rates below the labeled rate (70 g ha−1) provided 90% or greater control of common cocklebur, smallflower morningglory, and smooth pigweed if applied to 3 true-leaf or smaller weeds and of barnyardgrass, seedling johnsongrass, and Palmer amaranth if applied while weeds were in the cotyledon or 1 true-leaf stage. A rate of 70 g ha−1 provided 90% control of large crabgrass in the 1 true-leaf stage. Entireleaf morningglory, red rice, pitted morningglory, and velvetleaf are not susceptible enough to imazethapyr for 90% or greater control to be obtained with rates lower than 70 g ha−1 at the 1 true-leaf growth stage. These data demonstrate how control data can be used for developing effective reduced-rate herbicide recommendations based on weed leaf number.

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.

Field experiments were conducted in 1988 and 1989 to evaluate imazethapyr for weed control in peanuts. Imazethapyr was applied PRE or POST at 3, 5, or 7 weeks after crop emergence (WAE) at 0.071 kg ai ha–1. Imazethapyr applied PRE controlled common lambsquarters 85%, prickly sida 92%, and a mixture of entireleaf, ivyleaf, pitted, and tall morningglory species 77%. Morningglory control was at least 91% with imazethapyr plus metolachlor PRE followed by imazethapyr plus 2,4–DB or imazethapyr plus acifluorfen at 3, 5, or 7 WAE. Yields from systems that included metolachlor plus imazethapyr PRE followed by imazethapyr plus acifluorfen, imazethapyr plus 2,4–DB, or acifluorfen plus 2,4–DB at 3 WAE were greater than yields from the handweeded check. All systems with imazethapyr plus metolachlor PRE followed by any POST treatment except imazethapyr plus acifluorfen 7 WAE provided net returns equivalent to the herbicide standard of metolachlor PRE and acifluorfen and bentazon plus 2,4–DB 3 WAE. All systems except imazethapyr PRE provided greater net returns than the handweeded weed–free check.

Field experiments were conducted over a 3-yr period at three locations to evaluate lactofen at rates of 110 to 220 g ai ha−1 applied POST in combination with chlorimuron at 9 g ae ha−1 for weed control in soybean. At St. Joseph in 1989 and Baton Rouge in 1990, lactofen at 110, 150, and 170 g ha−1 in combination with chlorimuron controlled prickly sida (3 to 5 cm) and entireleaf and pitted morningglory (5 to 13 cm) comparable with the full rate of lactofen at 220 g ha−1 plus chlorimuron and the standard treatment of acifluorfen at 280 g ae ha−1 plus bentazon at 560 g ae ha−1. Entireleaf morningglory and sicklepod control at Alexandria with lactofen at 110 to 170 g ha−1 plus chlorimuron was comparable with that from the full rate of lactofen plus chlorimuron and better than with acifluorfen plus bentazon. Weed control was reduced when soil moisture was deficient at treatment time or when prickly sida height was more than 5 cm and entireleaf morningglory, pitted morningglory, and sicklepod more than 15 cm. In related studies at St. Joseph, a reduced rate of lactofen (170 g ha−1) in combination with chlorimuron controlled prickly sida 98%, pitted morningglory 93%, and entireleaf morningglory 90% in 1988, which was comparable with the control from the full rate of lactofen plus chlorimuron and with acifluorfen plus bentazon.

An experiment was conducted at four locations in North Carolina during 1994 and 1995 to evaluate weed control, cotton yield, fiber quality, and net returns in no-tillage bromoxynil-tolerant cotton. The experiment focused on using bromoxynil or pyrithiobac sodium applied early POST over-the-top as alternatives to fluometuron plus MSMA applied early POST directed. Fluometuron plus MSMA was more effective than bromoxynil or pyrithiobac sodium on tall morningglory, large crabgrass, goosegrass, and broadleaf signalgrass. Bromoxynil and fluometuron plus MSMA were similarly effective on common lambsquarters, common ragweed, and eclipta and more effective than pyrithiobac sodium. Pyrithiobac sodium and fluometuron plus MSMA were similarly effective on smooth pigweed and Palmer amaranth and more effective than bromoxynil. Prickly sida control by bromoxynil and pyrithiobac sodium was equal to or greater than control by fluometuron plus MSMA. All early POST herbicides controlled pitted morningglory similarly. Regardless of the early POST herbicides used, fluometuron applied PRE and cyanazine plus MSMA applied late POST directed increased control of most weeds and increased cotton yield and net returns. Bromoxynil and pyrithiobac sodium effectively substituted for fluometuron plus MSMA only in systems that included fluometuron applied PRE and cyanazine plus MSMA applied late POST directed. Effects of herbicide systems on cotton fiber quality were minor.

Clomazone was evaluated preplant incorporated (PPI) or post-transplant (PT) for weed control in sweet potatoes. No crop injury by clomazone was detected. Clomazone controlled (≥90%). broadleaf signalgrass, large crabgrass, barnyardgrass, and prickly sida at all rates and methods of application (MOA). Common cocklebur was controlled (≥93%) by clomazone at 1.1 kg ai ha-1 applied PT or at 3.4 kg ai ha-1 PPI in 1988 and at all rates and MOA in 1989. Clomazone did not control carpetweed.

Barnyardgrass 7 to 25 cm tall was controlled 48 to 74% with paraquat (420 g/ha), 83 to 87% with glyphosate (1120 g/ha), and 85 to 91% with glufosinate (840 g/ha). In most cases barnyardgrass control was not enhanced with addition of residual herbicides metribuzin plus chlorimuron, metribuzin, or imazaquin. Barnyardgrass and seedling johnsongrass no more than 13 cm tall was controlled at least 90% regardless of herbicide treatment. When rhizome and seedling johnsongrass were present, control with glyphosate was 96% compared with 55% for paraquat and 86% with glufosinate. Tank-mixtures of non-selective and residual herbicides generally enhanced control of entireleaf and pitted morningglory, hemp sesbania (15 to 30 cm), and prickly sida (15 to 18 cm). Soybean yields in most cases were not increased with addition of residual herbicides. Yield following glufosinate applied alone was 25% higher than following paraquat, and for all herbicide treatments yields were at least 45% greater than when a non-selective herbicide was not applied.

Methods were developed and evaluated that utilize state of the art weed-sensing technology in row-crop production systems. Spectral differences in green living plants and bare soil allowed ‘real-time’ weed detection, with intermittent spraying of herbicide only where weeds were present. Sensor units were mounted in 0.7-m-wide hooded sprayers providing sensors with an unobstructed view of the area between soybean rows. Single hood and commercial-size eight-row systems were evaluated, and savings in glyphosate spray solution applied using sensors ranged from 63 to 85%, compared to conventional hooded spray systems with continuous application. Weed control by the sensor-controlled spray system was equal to the conventional system. This technology can significantly reduce herbicide usage and decrease production cost without reducing weed control.

The effects of the plant growth regulator thidiazuron and the plant pathogen Colletotrichum coccodes on ethylene synthesis by velvetleaf and prickly sida were investigated. Untreated velvetleaf seedlings produced 1.5 and 2.3 pmol ethylene/mg fresh weight 24 and 48 h after treatment. Treatment with thidiazuron at 200 g ai/ha or C. coccodes at 1 × 109 spores/m2 increased ethylene production by 4.9 and 3.5 pmol/mg, respectively, in 24 h; and by 10.6 and 15.8 pmol/mg, respectively, in 48 h. Combination treatments caused synergistic increases in ethylene production by velvetleaf seedlings of 17.7 and 49.6 pmol/mg in 24 and 48 h, respectively. Thidiazuron at 10 μM, combined with an extract of C. coccodes mycelia, increased ethylene synthesis by more than 4-fold in vacuum-infiltrated excised velvetleaf petioles within 48 h. Thidiazuron at 50 g/ha, combined with an extract of C. coccodes mycelium, increased ethylene synthesis 16-fold in prickly sida seedlings in 24 h. Aminocyclopropane carboxylic acid (ACC), a precursor of ethylene, stimulated ethylene production by velvetleaf petioles more than 8-fold when supplied at 0.75 mM; thidiazuron and the pathogen effects were not discernible in its presence. Aminoethoxyvinyl-glycine (AVG), an inhibitor of ACC synthase, inhibited overall ethylene production by velvetleaf seedlings more than 40% when supplied at 0.58 to 0.67 mM, without obscuring the stimulatory effects of thidiazuron and the pathogen. These results indicate that the growth regulator and the plant pathogen or an extract of the pathogen act in concert to increase ethylene synthesis in velvetleaf. Stimulation probably occurs before the synthesis of ACC in the ethylene biosynthetic pathway.

Emergence periodicity of common purslane, hemp sesbania, horse purslane, prickly sida, spurred anoda, and velvetleaf was determined from March to October during 5 yr at Stoneville, MS, in the absence of reseeding. In early March of each year prior to emergence determinations, plots were not tilled or tilled to depths of 0, 5, 10, or 15 cm. Yearly emergence periodicity of the six weed species was not affected by tillage. In each year, weeds of all species emerged in identifiable flushes and very few emerged at other times during the growing season. Velvetleaf emerged mainly during the early growing season from March through May. Peak periods of emergence for the other species varied slightly over the 5 yr, but conformed generally to the early or the midseason peak period (June, July, and August) or both. In most years, common purslane, horse purslane, hemp sesbania, prickly sida, and spurred anoda emerged during the midseason period. Annual patterns of temperature fluctuations were similar during the 5 yr, but relatively warm soil temperatures during the early growing season of 1977 may have caused earlier emergence of velvetleaf, prickly sida, and hemp sesbania. Weekly water balance (rainfall minus open-pan evaporation) varied during March through May of each year but was negative during each June, July, and August. Apparently the main effect of a positive water balance during most of the year was to cause merger of the early and midseason peak emergence periods in 1979. Early and midseason emergence peaks were possibly due to different populations of seeds able to germinate in cooler soil temperatures of the early season and warmer soil temperatures of the midseason, respectively.

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.