Field experiments were conducted in 1989 and 1990 to evaluate seasonal effects of herbicide application, smutgrass (Sporobolus indicus) growth stage, and herbicide rate on smutgrass control. The experimental design was a split–split plot, with season (late spring, midsummer, and fall) as the whole plot, physiological stage at application (uncut, 15-, and 30-cm regrowth) the subplot, and hexazinone rate (0.0, 0.56, 0.84, and 1.12 kg ai/ha) as the sub-subplot treatment. Whole plots were arranged in three randomized complete blocks. Smutgrass control for the mean of the hexazinone treatments (1989 and 1990) was 95%. Application of 0.56 kg/ha hexazinone during late spring, midsummer, and fall seasons provided 77, 92, and 92% smutgrass control, respectively. Generally, the influence of plant stage at time of hexazinone application had no effect (P > 0.05) on smutgrass control. At 20 d after treatment (DAT), hexazinone had injured bahiagrass (Paspalum notatum) plants by yellowing them, but the plants reverted to their usual dark green color by 40 DAT. Total nonstructural carbohydrates were lower for the 30-cm regrowth than for the uncut plants, regardless of season; however, 30-cm regrowth had little effect on smutgrass control.

Greenhouse and field experiments were conducted to determine the response of corn (Zea mays), barnyardgrass (Echinochloa crus-galli), common lambsquarters (Chenopodium album), large crabgrass (Digitaria sanguinalis), velvetleaf (Abutilon theophrasti), and yellow foxtail (Setaria lutescence) to RPA 201772. Barnyardgrass, large crabgrass, velvetleaf, and common lambsquarters were more susceptible than yellow foxtail to RPA 201772. Velvetleaf was the most susceptible species and rates above 18 g ai/ha of RPA 201772 controlled 100% of the population 4 wk after treatment (WAT). Percent control of all the weed species increased with increased RPA 201772 rates. In the field, the dry weights of yellow foxtail decreased as the rate of RPA 201772 increased from 0 to 210 g/ha. However, a 60% reduction of dry weight of yellow foxtail was recorded at 140 g/ha of RPA 201772 compared to the untreated check 6 WAT, whereas at 12 WAT the dry weight of yellow foxtail was reduced to only 15% because of intraspecific competition. Yellow foxtail was moderately susceptible to RPA 201772. Corn was tolerant to RPA 201772; the GR80 value was 435 g/ha in the greenhouse. The bleaching injury to corn in the field was less than 10%, and it was found only with the 210 g/ha rate of RPA 201772. This injury was temporary and the plants recovered within 2 to 3 wk. Based on the GR80 values, velvetleaf was the most susceptible, followed by common lambsquarters, large crabgrass, barnyardgrass, and yellow foxtail.

Effectiveness of rotary hoeing with cultivation and comparison of an in-row cultivator with a standard row-crop cultivator were determined in dry edible bean. The effectiveness of in-row cultivation conducted at various timings and frequencies was examined. The in-row cultivator was more effective in reducing weed populations than the standard cultivator, although at least two mechanical weeding operations were needed to reduce weed populations to levels of the herbicide check (EPTC [S-ethyl dipropyl carbamothioate] plus ethalfluralin). When the in-row cultivation was delayed until the second trifoliolate stage or later, weed populations were greater than those in the herbicide check. In situations with high weed populations, rotary hoeing prior to cultivation was required to reduce weed populations to levels similar to the herbicide check. An in-row cultivator has potential to improve mechanical weed control options in a crop such as dry edible bean. The types of adjustments made in combination with soil textures, soil moisture, and operator experience affect overall weed control. Thus, it is expected that the level of weed control will vary from year to year and even field to field for the same operator.

Field studies in 1988 and 1989 evaluated POST herbicides alone and in tank-mixtures for tropic croton control in peanut. Acifluorfen + 2,4-DB, acifluorfen + bentazon, acifluorfen + bentazon + 2,4-DB controlled > 90% of tropic croton when applied at 2 or 4 wk after crop emergence. Paraquat + bentazon controlled 55% at 2 wk and 24% at 4 wk after crop emergence. Imazethapyr and imazethapyr + 2,4-DB controlled < 24% tropic croton at either 2 or 4 wk after crop emergence. Acifluorfen + 2,4-DB, acifluorfen + bentazon, and acifluorfen + bentazon + 2,4-DB controlled at least 90% of the common lambsquarters, common ragweed, and morningglory species. Greatest yields and net returns were obtained with acifluorfen + bentazon + 2,4-DB applied 2 wk after crop emergence. Yields were higher with acifluorfen + bentazon + 2,4-DB and imazethapyr applied at 2 wk after crop emergence than at 4 wk after crop emergence. All other herbicide treatments provided equivalent yields among application timings. Only acifluorfen + 2,4-DB provided equivalent net returns at either application timing. All other herbicide treatments provided lower net returns with applications made at 4 wk than at 2 wk after crop emergence.

Greenhouse studies were conducted to evaluate shoot number, shoot weight, rhizome weight, and root weight reduction of green and false-green kyllinga at three placement levels (soil applied, foliar applied, and soil + foliar applied) and five herbicide treatments (CGA-362622, halosulfuron, imazaquin, MSMA, and imazaquin + MSMA). Averaged over herbicide and placement level, false-green kyllinga shoot number 30 d after treatment (DAT) and rhizome weight 60 DAT were reduced more than those of green kyllinga. Furthermore, imazaquin, MSMA, and imazaquin + MSMA, averaged across placement levels, as well as CGA-362622 and halosulfuron, both foliar and soil applied, reduced false-green kyllinga shoot number greater than that of green kyllinga 60 DAT. Halosulfuron reduced false-green kyllinga shoot weight greater than that of green kyllinga 60 DAT; however, MSMA reduced green kyllinga greater. In general, foliar- and soil + foliar–applied treatments reduced shoot number (30 DAT), rhizome weight, and root weight of both kyllinga species greater than soil-applied treatments, whereas soil + foliar–applied treatments were more effective in reducing shoot weight 60 DAT. CGA-362622 and halosulfuron reduced kyllinga species shoot number (30 DAT), false-green kyllinga shoot weight (60 DAT), and root weight of both species greater than all other herbicides. However, CGA-362622 reduced green kyllinga shoot weight (60 DAT) and rhizome weight of both species greater than all other herbicides.

A greenhouse experiment was conducted from 1995 to 1996 to determine the inheritance of ALS-cross-resistant common cocklebur. Two known biotypes (ALS-susceptible and ALS-resistant) were used in the experiment. Susceptible biotypes were crossed with pollen from resistant biotypes. F1 plants were self-pollinated. F2 plants were sprayed postemergence (POST) with a tank mixture of imazaquin at 280 g ai/ha and chlorimuron at 18 g ai/ha. Three distinct responses were observed: (1) no apparent effect (resistant), (2) yellowing of leaves with live terminals (intermediate), and (3) yellow leaves with dead terminals (typical symptoms of an ALS-susceptible common cocklebur). Chi-square tests indicated that an incomplete dominance model did not fit the data. Responses one and two were, therefore, combined and chi-square tests indicated a complete dominance model fit the data. This indicates that the cross-resistant trait is a dominant to semidominant trait.

A field study was conducted in 1994 and 1995 to determine the effect of MON 12037, linuron, and ametryn on purple nutsedge density in field corn in a 2-yr rotation with cotton. Each corn treatment included cultivation and noncultivation. A standard treatment for purple nutsedge control was applied to all cotton plots in the second season of the corn–cotton rotation. Purple nutsedge shoot densities were reduced in cultivated MON 12037, noncultivated MON 12037, and cultivated ametryn in the corn–corn and corn–cotton rotations. Purple nutsedge tuber population was reduced in the corn–corn rotation by MON 12037 with and without cultivation, cultivated linuron, and cultivated ametryn treatments relative to the noncultivated check. In the corn–cotton rotation, purple nutsedge tuber population was reduced only by the cultivated MON 12037 and cultivated ametryn treatments relative to the noncultivated check.

Field experiments were conducted in 2001 and 2002 to study the effect of date of planting, herbicide, and straw mulch on menthol mint yield and oil quality in northwest India. Menthol mint was planted at three dates (December 10, December 30, and January 20). Diuron was applied prior to emergence at rates of 0.0, 0.4, and 0.6 kg ai/ha, with and without rice straw mulch (6 t/ha). Menthol mint planted on December 30 and January 20 produced more plantlets and dry matter than the December 10 planting. Menthol mint planted on December 10 had higher weed density and weed biomass, and lower menthol mint herbage and oil yield than the later planting dates. Straw mulch application reduced weed density and weed biomass, and increased plantlet population, menthol mint dry matter accumulation, fresh herbage, and menthol mint oil yield. Preemergence (PRE) applications of diuron at 0.4 and 0.6 kg ai/ha increased menthol mint population and crop dry matter accumulation, and decreased weed density and weed biomass compared to the weedy check. Diuron at 0.6 kg/ha increased fresh herbage and menthol mint oil yield over the untreated weedy check, but there were no other differences between the two rates of diuron. Physicochemical properties of menthol mint oil were not affected by any of the three tested factors.

Greenhouse and field experiments were conducted at Athens, GA, during 1984 and 1985 to evaluate the interference of several soybean cultivars with sicklepod. The 12 soybean cultivats evaluated in the field were commonly used from 1907 to the present. No correlation of soybean cultivar maturity group or date of introduction with interference on sicklepod was observed. ‘Essex’ and ‘Bragg’ soybean reduced sicklepod dry weight in the field; however, only Essex was unaffected by sicklepod. In the greenhouse experiments, root and shoot growth of sicklepod was less than the cultivars ‘CNS', ‘Peking’, and ‘Forrest’. Sicklepod produced the least above- and below-ground growth while ‘CNS' produced the most of the three cultivars. When grown together, the combined total root growth of each cultivar plus sicklepod was less than calculated expected values. The genetic development of soybean cultivars with improved tolerance to sicklepod infestations possibly could reduce weed control inputs.

Field studies were conducted in 1987 and 1988 at Fayetteville and Clarkedale, AR, to evaluate various herbicide treatments for johnsongrass control in soybeans. Herbicide treatments were postemergence applications of sethoxydim, fenoxaprop, fluazifop-P, haloxyfop, quizalofop, imazethapyr, and clethodim. No significant soybean injury was noted in 1987 or 1988 at either location in the johnsongrass experiments. All treatments except those with fenoxaprop and imazethapyr, provided 70 to 90% johnsongrass control. Generally, soybean yields were reduced from treatments that controlled less than 60% of the johnsongrass.

With increasing incidence of glyphosate-resistant weeds worldwide, greater farmer awareness of the importance of glyphosate stewardship and proactive glyphosate-resistance management is needed. A Web-based decision-support tool (http://www.weedtool.com) comprising 10 questions has been developed primarily for farmers in western Canada to assess the relative risk of selection for glyphosate-resistant weeds on a field-by-field basis. We describe the rationale for the questions and how a response to a particular question influences the risk rating. Practices with the greatest risk weighting in western Canadian cropping systems are lack of crop-rotation diversity (growing mainly oilseeds) and a high frequency of glyphosate-resistant crops in the rotation. Three case scenarios are outlined—low, moderate, and high risk of glyphosate-resistance evolution. Based on the overall risk rating, three best-management practices are recommended to reduce the risk of glyphosate resistance in weeds.

Experiments were conducted to evaluate the effect of tillage, rye residue levels, and control strategies on weed suppression and potato yield. Reduced tillage (RT) yields in 1989 were lower than in conventional tillage (CT) due to high hairy galinsoga populations. However, in 1990, potato yields were greater in RT when early emerging weeds were suppressed. Increasing residue levels up to 2300 kg ha−1 had no effect on weeds or yields in either year. In a separate study, preemergence herbicides (linuron plus metolachlor, 1.7 kg ai ha−1 each) applied 10 d after planting (DAP) in reduced tillage controlled weeds for 6 wk, but efficacy decreased after hilling. Metribuzin applied postemergence (0.19 kg ai ha−1) 7 d after hilling controlled late germinating weeds. Potato yields were greatest when the preemergence herbicides were applied.

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.

Field studies were conducted in 2000, 2001, and 2002 at Brownstown, DeKalb, Perry, and Urbana, IL, to evaluate weed control and corn tolerance from postemergence (POST) applications of foramsulfuron in sequential and total-POST herbicide programs. Foramsulfuron applied alone controlled giant foxtail, fall panicum, and redroot pigweed 88, 99, and 99%, respectively, 28 d after treatment (DAT), which was comparable with the standard treatment of nicosulfuron. However, control of common cocklebur, velvetleaf, and common lambsquarters was significantly higher with foramsulfuron compared with nicosulfuron. Sequential herbicide programs of atrazine, S-metolachlor, or isoxaflutole applied preemergence (PRE) followed by a POST application of foramsulfuron provided greater than 85% control of giant foxtail, fall panicum, common cocklebur, velvetleaf, common waterhemp, and redroot pigweed. Of the sequential herbicide treatments, atrazine applied PRE followed by a POST application of foramsulfuron provided the greatest Pennsylvania smartweed control. A PRE application of either atrazine or isoxaflutole was needed before a POST application of foramsulfuron to control common lambsquarters. POST tank mixtures of foramsulfuron with atrazine, dicamba, and dicamba plus diflufenzopyr improved control of Pennsylvania smartweed, common cocklebur, velvetleaf, common lambsquarters, and common waterhemp when compared with foramsulfuron applied alone. The tank mixture of foramsulfuron with mesotrione improved control of all species, except Pennsylvania smartweed, common lambsquarters, and common cocklebur. Foramsulfuron tank mixtures with carfentrazone did not improve control of any weed species to commercial acceptance. Adjuvant selection was important for POST tank mixtures. Control of giant foxtail and fall panicum was reduced when atrazine was tank mixed with foramsulfuron and crop oil concentrate (COC). However, when methylated seed oil (MSO) was added to the atrazine–foramsulfuron tank mixture instead of COC, giant foxtail and fall panicum control were similar to foramsulfuron applied alone.

Detectspray™ weed-activated sprayer (WAS) technology enables individual nozzles on a sprayer to turn on and off in response to the presence of green vegetation. WAS operated full season at two fallow sites in North Dakota reduced POST herbicide requirement 47 to 88%. Full-season WAS applied as needed at West Fargo reduced cost to the farmer by only 13% compared with broadcast application with a farmer-owned sprayer and assuming free labor. Winds of 8 to 16 km/h apparently moved spray off target, thereby necessitating retreatment and increasing the relative costs of WAS at Fargo. The percentage of sample quadrats having greater than 3% vegetative cover correlated positively (r = 0.78 to 0.80) with percentage reduction in spray volume achieved by WAS.

Sulfonylurea herbicide residues in soil can affect rotational crops even at low concentrations. Although analytical methods are efficient enough to measure them, the lack of an efficient herbicide extraction technique makes bioassays useful for determining the presence of phytotoxic levels of sulfonylurea residues in soil. A growth chamber bioassay using sunflower was developed to detect MON-37500 and triasulfuron residues in two different soils. Root length was measured 15 d after the treatment. A sigmoid equation described plant root length response as a function of herbicide concentration. The nonlinear regression established a range of I50 values from 0.9 to 2.9 ppb ai for both sulfonylureas.

Greenhouse and field studies were conducted to evaluate potential interactions between glyphosate and trifloxysulfuron on barnyardgrass, browntop millet, hemp sesbania, seedling johnsongrass, pitted morningglory, prickly sida, sicklepod, and velvetleaf control as well as cotton injury and yield. In the greenhouse, glyphosate at 840 g ae/ha controlled all weed species 62 to 99%, which was better than trifloxysulfuron at 2.5 or 5 g ai/ha. Control of four-leaf pitted morningglory and hemp sesbania was 80 to 88% when glyphosate and trifloxysulfuron were mixed compared with 62 to 66% control with glyphosate alone. Mixing trifloxysulfuron with glyphosate did not affect control of other species compared with glyphosate alone. In the field, glyphosate controlled barnyardgrass, prickly sida, sicklepod, seedling johnsongrass, and velvetleaf 68 to 100%. Trifloxysulfuron controlled hemp sesbania, seedling johnsongrass, and sicklepod 65 to 88%. All other species were controlled 36 to 72% with glyphosate and 10 to 60% with trifloxysulfuron. Combinations of glyphosate (840 g/ha) and trifloxysulfuron (5 g/ha) were applied postemergence over-the-top and postemergence-directed to three-, six-, and nine-leaf glyphosate-resistant cotton in the field. Cotton injury at 2 wk after treatment (WAT) was less than 13% for all herbicide treatments and less than 5% by 3 WAT. Herbicides did not affect the percent of open bolls or nodes per plant. Seed cotton yield ranged from 1,430 to 1,660 kg/ha, and only the sequential over-the-top applications of trifloxysulfuron reduced cotton yield compared with the weed-free, nontreated cotton.

MON 37500 was registered in 1999 for weed control in wheat and has the potential to injure following crops. Therefore, growth chamber experiments were conducted to determine the effect of soil properties on the phytotoxicity of MON 37500 residues, the relative tolerance of several potential rotational crops, and the joint effect of MON 37500 residues plus other herbicide residues on a susceptible crop. In 13 Alberta soils, the concentrations of MON 37500 and triasulfuron that reduced canola and barley dry matter by 50% (GR50) were correlated with soil organic matter (OM) and pH. The relationship that best described the effect of soil organic matter on GR50 for each herbicide–crop combination was GR50 = a + b(OM)2. There was no significant improvement in r 2 when pH and clay content were included in the equation. For soils with 2 and 10% OM content, predicted GR50 values for canola in MON 37500–treated soil are 2 and 26 ηg/g soil, respectively. Little injury to following canola is predicted in soils with OM contents > 4.5%. At similar concentrations, following crops such as canola, flax, lentil, and oriental mustard are predicted to be injured less by MON 37500 than by triasulfuron. The effect of combined residues of MON 37500 with triasulfuron, imazethapyr, or metsulfuron should be additive.

Glyphosate and SC-0224 at 75 or 150 g ae/ha, applied to alfalfa foliage after field dodder and largeseed dodder were parasitically well established, controlled dodder selectively. Glyphosate applied at any time over a range of developmental stages stopped the growth of dodder. Control was best when the herbicides were applied when alfalfa was 20 to 30 cm tall, when maximum length of dodder shoots was 30 to 60 cm, and while host and parasite were both vegetative and growing vigorously. Later application allowed dodder to injure alfalfa before being controlled, and earlier application sometimes allowed dodder to recover and suppress alfalfa before the hay was cut.

Sustainable weed management strategies are needed for organic orchard systems. A study was conducted in an almond orchard in Fresno, CA from 2009 to 2011. Treatment comparisons included steam, flame, and broad applications of either lemongrass oil or D-limonene. An untreated control was also included. The experimental design was a randomized complete block with four replications. Weekly evaluations on percent weed control were taken and weed biomass was sampled 4 to 8 wk after treatment (WAT). Weed control and biomass differed between seasons but, in general, steam and flame provided as much as 95% control 1 WAT. However, the effects lasted only 3 to 4 wk as new weeds emerged or the treated weeds overcame the suppressive effects of the thermal treatments. Weed biomass was 95% lower in the steam- and flame-treated plots compared with the untreated plots in summer. Both steam and flame were more effective on certain erect-growing broad-leaved weed species than on prostrate-growing weeds and grasses. Lemongrass oil provided very little weed control. However, D-limonene provided up to 95% weed control 1 WAT and in one experiment 53% control was observed up to 5 WAT. This herbicide also resulted in lower weed biomass than the untreated and the thermal-treated plots. Monthly applications of steam or flame or applications of D-limonene every 5 to 6 wk may have to be made to adequately suppress weeds in organic almond orchards. Cost estimates of propane use were $41 to 56 ha−1 and $26 ha−1 for the steam and flame treatments, respectively. The cost of D-limonene was estimated as $275 ha−1. To optimize weed control and costs, these tools may need to be used in combination rather than by themselves.