An experiment was conducted at two locations in Georgia and one location in North Carolina during 1994 and 1995 to evaluate weed management systems utilizing pyrithiobac applied preemergence (PRE) in conventional-tillage bromoxynil-resistant cotton. Weed management systems evaluated included different combinations of pyrithiobac PRE, bromoxynil or bromoxynil plus MSMA applied early postemergence (EPOST), bromoxynil applied postemergence (POST), and cyanazine plus MSMA applied late postemergence-directed (LAYBY). Pyrithiobac PRE improved control of Florida beggarweed, pitted morningglory, prickly sida, sicklepod, and spurred anoda compared with systems that did not include pyrithiobac PRE. Averaged across locations, pyrithiobac PRE increased cotton lint yields 330 kg ha−1. Bromoxynil applied EPOST or POST increased weed control and cotton lint yield. Bromoxynil EPOST, POST, or EPOST plus POST did not control sicklepod. The addition of MSMA to bromoxynil EPOST improved sicklepod control. Two applications of bromoxynil controlled more pitted morningglory and sicklepod than one application. Control of all dicotyledonous weeds was increased by cyanazine plus MSMA LAYBY, and this treatment increased yields at all locations. Cotton was not injured by pyrithiobac PRE or by bromoxynil applied EPOST or POST, but temporary visual injury was observed with EPOST treatments of MSMA.

An experiment conducted at five locations in North Carolina during 1998 and 1999 evaluated weed management systems in cotton with CGA-362622 and pyrithiobac. Weed management systems evaluated different combinations with or without fluometuron preemergence (PRE) followed by (fb) CGA-362622 early postemergence (EPOST), postemergence (POST), or EPOST + POST; or pyrithiobac EPOST fb prometryn plus MSMA late postemergence directed (LAYBY) or no LAYBY treatment. The weed species evaluated include common ragweed, entireleaf morningglory, pitted morningglory, prickly sida, sicklepod, tall morningglory, and yellow nutsedge. Fluometuron PRE improved the control of all weed species by at least 17 percentage points and increased cotton lint yield compared with the systems that did not use fluometuron PRE. Prometryn plus MSMA LAYBY improved the control of all weed species and increased lint yield compared with the systems that did not use prometryn plus MSMA LAYBY when PRE or POST herbicides were used. Control with CGA-362622 at all application timings was greater than 70% for all weed species evaluated (common ragweed, entireleaf morningglory, pitted morningglory, sicklepod, tall morningglory, and yellow nutsedge), except prickly sida. Control of all three morningglory species and prickly sida was at least 70% with pyrithiobac, whereas control of common ragweed, sicklepod, and yellow nutsedge was lower. The only cotton that yielded over 800 kg ha−1 was treated with fluometuron PRE fb CGA-362622 EPOST, POST, or EPOST + POST fb prometryn plus MSMA LAYBY. Cotton treated with pyrithiobac EPOST gave yields that were similar to those given by cotton treated with CGA-362622 EPOST in systems with fluometuron PRE and less than those given by cotton treated with CGA-362622 EPOST in systems without fluometuron PRE. Early-season injury with CGA-362622 was greater than 60% at Clayton and Rocky Mount in 1998, whereas 12% or less injury was observed at the other locations. Pyrithiobac resulted in 25 to 45% injury at these two locations. No injury was observed 45 d after treatment.

Field and greenhouse studies were conducted to investigate the compatibility of MSMA in a tank mixture with glyphosate or glufosinate for broadleaf and grass weed control. Glyphosate, glufosinate, and MSMA were evaluated at 0.5×, 1×, and 2× rates, with 1× rates of 0.84 kgae/ha, 0.5 kgai/ha, and 2.2 kgai/ha, respectively. Glyphosate and glufosinate provided similar levels of control for most weed species and were often more efficacious than MSMA alone. Glyphosate controlled Palmer amaranth better than glufosinate. Glufosinate controlled hemp sesbania, pitted morningglory, and ivyleaf morningglory better than glyphosate at one location. Weed control was not improved with the addition of MSMA to glyphosate or glufosinate when compared with either herbicide alone. MSMA antagonized glyphosate efficacy on barnyardgrass, browntop millet, hemp sesbania, Palmer amaranth, and redroot pigweed. MSMA antagonized glufosinate efficacy on browntop millet, hemp sesbania, ivyleaf morningglory, johnsongrass, Palmer amaranth, pitted morningglory, prickly sida, redroot pigweed, and velvetleaf. Antagonism of glyphosate or glufosinate by MSMA was often overcome by applying the 2× rate of either herbicide alone. MSMA is not a compatible tank-mixture partner with glyphosate or glufosinate for weed control in cotton.

Studies were conducted to evaluate uptake, translocation, and metabolism of root-absorbed 14C-sulfentrazone in peanut, prickly sida, and pitted morningglory. Peanut absorbed more than five and three times greater 14C-sulfentrazone than pitted morningglory and prickly sida, respectively. All plant species translocated appreciable amounts (≥ 39%) of radioactivity to the leaves. The three plant species had some capacity to metabolize 14C-sulfentrazone. At 3 h after treatment, 7, 29, and 71% of the radioactivity in the shoots of peanut, prickly sida, and pitted morningglory, respectively, was sulfentrazone. Sulfentrazone levels in the shoots at 3 and 6 h after treatment correspond to reported tolerance levels, with peanut being the most tolerant of the three species, whereas prickly sida and pitted morningglory are moderately tolerant and completely susceptible to sulfentrazone, respectively. Levels of metabolites varied among species, plant part, and harvest timing. On the basis of these data, tolerance in peanut is largely due to its ability to rapidly metabolize sulfentrazone.

Experiments were conducted in Lewiston, NC, in 1999 and 2000 and Rocky Mount, NC, in 1999 to evaluate weed management systems in strip- and conventional-tillage peanut. The peanut cultivars grown were ‘NC 10C’, ‘NC 12C’, and ‘NC 7’, respectively. Weed management systems consisted of different combinations of preemergence (PRE) herbicides including diclosulam and flumioxazin plus commercial postemergence (POST) herbicide systems. Dimethenamid plus diclosulam or flumioxazin PRE controlled common lambsquarters, eclipta, and prickly sida at least 91%. Diclosulam and flumioxazin provided variable control of three Ipomoea species (59 to 91%) and bentazon plus acifluorfen POST provided > 90% control. Only diclosulam systems controlled yellow nutsedge 90% late season. Annual grass control required clethodim late POST, regardless of tillage system. Dimethenamid plus diclosulam or flumioxazin PRE produced equivalent yields and net returns with no significant differences between the two PRE options. Both systems produced higher yields and net returns than dimethenamid regardless of the POST herbicide option. The tillage production system did not influence weed control of eight weeds, peanut yields, or net returns. The addition of diclosulam or flumioxazin to dimethenamid PRE improved weed control compared with dimethenamid PRE alone.

Studies were conducted to evaluate weed management systems in nontransgenic, bromoxynil-resistant, and glyphosate-resistant cotton in strip- and conventional-tillage environments. Tillage did not affect weed control, cotton lint yields, or net returns. Early season stunting in strip-tillage cotton was 5% or less, regardless of herbicide system or cultivar and was transient. Excellent (> 90%) control of common lambsquarters, common ragweed, and Ipomoea species, including entireleaf, ivyleaf, pitted and tall morningglories, jimsonweed, prickly sida, and velvetleaf, was achieved with systems containing bromoxynil, glyphosate, and pyrithiobac early postemergence (EPOST). Glyphosate systems provided better and more consistent control of fall panicum and large crabgrass than bromoxynil and pyrithiobac systems. Bromoxynil and pyrithiobac EPOST did not control sicklepod unless applied in mixture with MSMA and followed by (fb) a late postemergence-directed (LAYBY) treatment of prometryn plus MSMA. Palmer amaranth was controlled (> 90%) with all glyphosate and pyrithiobac systems and with the bromoxynil system that included a broadcast soil-applied herbicide treatment. Bromoxynil systems without a broadcast soil-applied herbicide treatment controlled Palmer amaranth 87% or less. Herbicide systems that included glyphosate EPOST controlled sicklepod with or without a soil-applied herbicide treatment. The highest yielding cotton included all the glyphosate systems and bromoxynil systems that contained a soil-applied herbicide treatment. Nontransgenic systems that included a soil-applied herbicide treatment yielded less than a system with soil-applied treatment plus glyphosate EPOST. Net returns from glyphosate systems were generally higher than net returns from bromoxynil or pyrithiobac systems.

Field and laboratory studies were conducted to evaluate herbicide efficacy, absorption, and translocation of cloransulam within broadleaf weeds. Control of morningglory species and velvetleaf with cloransulam was dependent upon application rate and timing. A reduced rate of cloransulam (9 g ai ha−1) was as effective as the labeled rate (18 g ha−1), when applications were targeted to small to midsize morningglory and velvetleaf. Prickly sida, hemp sesbania, and sicklepod were suppressed by cloransulam. Contour maps predicted accurately weed control for all species except tall morningglory. Cloransulam absorption and translocation provided some information about tolerance mechanisms. Susceptible species, entireleaf morningglory and velvetleaf, both rapidly absorbed 14C-cloransulam. Absorption in the more tolerant velvetleaf was 20% lower than entireleaf morningglory at all harvest times. Absorption of 14C-cloransulam in prickly sida was only 26% 6 h after treatment, and absorption did not increase with time. Differences in cloransulam absorption and translocation partially explained differences in susceptibility among some weed species but not others.

Field studies conducted at three locations in North Carolina in 1998 and 1999 evaluated crop tolerance, weed control, and yield with CGA-362622 alone and in combination with various weed management systems in transgenic and nontransgenic cotton systems. The herbicide systems used bromoxynil, CGA-362622, glyphosate, and pyrithiobac applied alone early postemergence (EPOST) or mixtures of CGA-362622 plus bromoxynil, glyphosate, or pyrithiobac applied EPOST. Trifluralin preplant incorporated followed by (fb) fluometuron preemergence (PRE) alone or fb a late POST–directed (LAYBY) treatment of prometryn plus MSMA controlled all the weed species present less than 90%. Herbicide systems that included soil-applied and LAYBY herbicides plus glyphosate EPOST or mixtures of CGA-362622 EPOST plus bromoxynil, glyphosate, or pyrithiobac controlled broadleaf signalgrass, entireleaf morningglory, large crabgrass, Palmer amaranth, prickly sida, sicklepod, and smooth pigweed at least 90%. Only cotton treated with these herbicide systems yielded equivalent to the weed-free check for each cultivar. Bromoxynil systems did not control Palmer amaranth and sicklepod, pyrithiobac systems did not control sicklepod, and CGA-362622 systems did not control prickly sida.

At the time of grain harvest, weed seeds can be classed into one of four pools on the basis of dispersal status and location: (1) undispersed, remaining on the mother plant; (2) dispersed in the current year, on the soil surface; (3) dispersed in the current year and collected by harvest machinery; and (4) dispersed in a previous year and persisting within the soil seed bank. Knowledge of the relative sizes of these seed pools for different weed species under different crop environments will be useful for determining the best way to reduce the size of inputs to the soil seed bank. In fall 2004 and fall 2005, four randomly selected commercially managed corn and soybean fields in east-central Illinois were sampled to quantify weed seed pools at time of crop harvest. Thirty randomly located 0.125-m2 quadrats were placed within each field, the four seed pools mentioned above were sampled for each quadrat, and the species composition and abundance of each seed pool was determined. The magnitude of the weed seed rain varied among species and between years and crops. Twenty-six weed species were found to contribute to at least one of the four seed pools. However, the weed seed pools were consistently dominated by six species: velvetleaf, Amaranthus complex (redroot pigweed and waterhemp), ivyleaf morningglory, giant foxtail, prickly sida, and common cocklebur. For each of these species, the ratio of undispersed seeds to seeds in the soil seed bank at harvest time was ≥ 1 in at least one crop during one of the two experimental years, indicating a potential for the soil seed bank to be completely replenished or augmented by that year's seed rain. This analysis demonstrates the urgent need for techniques to limit weed seed inputs to the soil seed bank at the end of the growing season.

Cotton gins in Arkansas, western Tennessee, and western Mississippi were sampled for weed seed contamination of gin trash in fall 2007. A total of 473 samples were collected, with 453 samples from Arkansas. The objectives of this research were to determine the weed species most frequently found in gin trash and determine what means gin operators are using to dispose of gin trash. There were 25 weed species found in the gin trash samples—11 grass and 14 broadleaf weeds. Grass and broadleaf weeds were present in 41.4 and 8.5% of the samples, respectively. The most frequently found species were large crabgrass (19.0%), barnyardgrass (14.0%), goosegrass (12.9%), red sprangletop (8.2%) and Palmer amaranth (4.2%). Viable seeds of barnyardgrass, large crabgrass, Palmer amaranth, and prickly sida were present in the surface layer (0- to 25-cm depth) of gin trash piles after 1 yr of composting. Viable Palmer amaranth seeds were present in the surface layer of gin trash piles after 2 yr of composting, but no germinable seeds were found deeper than 25 cm following 1 yr of composting. Gin trash disposal involved application of the material to crop fields during the fall or winter months; composting followed by application of the compost as mulch or a soil amendment to gardens, flower beds, or crop fields; use as cattle feed; and coverage for landfills to reduce erosion and encourage growth of vegetation. Because of the demonstrated potential for weed seed dispersal via gin trash, including composted material, development of technologies to ensure disposal of a gin-trash product free of viable weed seed are justified.

Field experiments were conducted to evaluate weed control provided by glyphosate, glufosinate, and MSMA applied alone or in mixture with residual and nonresidual last application (LAYBY) herbicides. Herbicide treatments included glyphosate early postemergence (EPOST) alone or followed by glyphosate, glufosinate, or MSMA late-postemergence (LPOST) alone or tank-mixed with one of the following LAYBY herbicides: carfentrazone-ethyl at 0.3 kg ai/ha, diuron at 1.12 kg ai/ha, flumioxazin at 0.07 kg ai/ha, fluometuron at 1.12 kg ai/ha, lactofen at 0.84 kg ai/ha, linuron at 0.56 kg ai/ha, oxyfluorfen at 1.12 kg ai/ha, prometryn at 1.12 kg ai/ha, or prometryn + trifloxysulfuron at 1.12 kg ai/ha + 10 g ai/ha. Residual herbicides were also applied alone LPOST. Weeds evaluated included barnyardgrass, broadleaf signalgrass, coffee senna, entireleaf morningglory, hemp sesbania, ivyleaf morningglory, johnsongrass, large crabgrass, Palmer amaranth, pitted morningglory, prickly sida, redroot pigweed, sicklepod, smooth pigweed, spiny amaranth, and velvetleaf. Treatments containing MSMA provided lower average weed control compared to those containing glyphosate or glufosinate, and residual herbicides applied alone provided inadequate weed control compared to mixtures containing a nonresidual herbicide. Across 315 of 567 comparisons (55%), when a LAYBY herbicide was added, weed control increased. The most difficult to control weed species at all locations was pitted morningglory. Barnyardgrass and hemp sesbania at the Mississippi location and hemp sesbania at the Louisiana location were collectively difficult to control across all treatments as well.

Rice by-products were evaluated in the greenhouse for herbicidal activity on various weeds and crops. Rice by-products and corn gluten meal (CG) were applied at 0, 125, 250, 500, and 750 g m−2 preemergence (PRE) and preplant incorporated (PPI). The efficacy of rice by-products and CG in reducing weed emergence and shoot weight of broadleaf species was in the order of medium-grain fatty rice bran (MF) > long-grain fatty rice bran (LF) > CG > defatted rice bran (DF) > long-grain hull (LH) > medium-grain hull (MH). For reducing grass emergence, MF = CG > LF > DF > LH > MH, and for shoot weight reduction, CG > MF > LF > LH > DF = MH. Palmer amaranth and ivyleaf morningglory were the most susceptible weeds (91 and 82%) followed by sicklepod, hemp sesbania, and prickly sida (65 to 70%). Velvetleaf was the most tolerant broadleaf weed. Grasses were not as susceptible to rice bran as broadleaf weeds. In general, MF was the best material for reducing weed emergence and its efficacy was not affected by application method. Cotton and corn were the most tolerant direct-seeded crops to MF (6% reduction in plant stand), and soybean, Italian ryegrass, tomato, and rice had intermediate tolerances (30 to 86% stand reduction). Mustard, cucumber, and lettuce were the most susceptible crops (71 to 98% reduction in plant survival). The minimum effective rate was 250 g m−2 MF PPI or PRE.

An experiment was conducted to determine the utility of multispectral imagery for identifying soybean, bare soil, and six weed species commonly found in Mississippi. Weed species evaluated were hemp sesbania, palmleaf morningglory, pitted morningglory, prickly sida, sicklepod, and smallflower morningglory. Multispectral imagery was analyzed using supervised classification techniques based upon 2-class, 3-class, and 8-class systems. The 2-class system was designed to differentiate bare soil and vegetation. The 3-class system was used to differentiate bare soil, soybean, and weed species. Finally, the 8-class system was designed to differentiate bare soil, soybean, and all weed species independently. Soybean classification accuracies classified as vegetation for the 2-class system were greater than 95%, and bare soil classification accuracies were greater than 90%. In the 3-class system, soybean classification accuracies were 70% or greater. Classification of soybean decreased slightly in the 3-class system when compared to the 2-class system because of the 3-class system separating soybean plots from the weed plots, which was not done in the 2-class system. Weed classification accuracies increased as weed density or weeks after emergence (WAE) increased. The greatest weed classification accuracies were obtained once weed species were allowed to grow for 10 wk. Palmleaf morningglory and pitted morningglory classification accuracies were greater than 90% for 10 WAE using the 3-class system. Palmleaf morningglory and pitted morningglory at the highest densities of 6 plants/m2 produced the highest classification accuracies for the 8-class system once allowed to grow for 10 wk. All other weed species generally produced classification accuracies less than 50%, regardless of planting density. Thus, multispectral imagery has the potential for weed detection, especially when being used in a management system when individual weed species differentiation is not essential, as in the 2-class or 3-class system. However, weed detection was not obtained until 8 to 10 WAE, which is unacceptable in production agriculture. Therefore, more refined imagery acquisition with higher spatial and/or spectral resolution and more sophisticated analyses need to be further explored for this technology to be used early-season when it would be most valuable.

Studies were conducted to evaluate weed management programs in nontransgenic, bromoxynil-resistant, and glyphosate-resistant cotton in nontilled and tilled environments. Tillage did not affect weed control provided by herbicides. Early-season stunting in nontilled cotton was 3% regardless of the herbicide system and was no longer evident at midseason. Cotton yield was 10 to 15% greater, on an average, under tilled conditions than that under nontilled conditions. Excellent (> 90%) common lambsquarters, entireleaf morningglory, ivyleaf morningglory, jimsonweed, pitted morningglory, prickly sida, tall morningglory, and velvetleaf control was achieved with treatments containing pyrithiobac, bromoxynil, and glyphosate. Preemergence (PRE) or postemergence-directed (PD) herbicide inputs were necessary for adequate large crabgrass and goosegrass control. Bromoxynil and pyrithiobac postemergence did not control sicklepod unless supplemented with MSMA and followed by a late-postdirected treatment of cyanazine plus MSMA. Treatments that included glyphosate controlled sicklepod regardless of the late-PD treatment. Economic returns were at least $930 ha−1 and not different from the higher yielding programs in nontransgenic cotton when fluometuron applied PRE was included in the bromoxynil programs. Late-season weed control was usually greater than 90% from glyphosate programs, and net returns from glyphosate programs were as high or higher than the net returns from programs that used midseason treatments of bromoxynil, pyrithiobac, or fluometuron plus MSMA.