Field trials were conducted to determine the effect of fumigant-pebulate combinations on purple nutsedge density in fresh market tomato. Treatments consisted of methyl bromide plus chloropicrin (MBr plus Pic) [67:33] at rates of 270 and 130 kg/ha, respectively; Pic plus pebulate at 400 and 4.5 kg/ha, respectively; metham (MNa) plus pebulate at 485 and 4.5 kg/ha, respectively; dazomet plus pebulate at 950 and 4.5 kg/ha, respectively; and 1,3-dicholopropene plus Pic (C-17) [87:13] plus pebulate at 392 and 4.5 kg/ha, respectively. At 12 wk after treatment, MBr plus Pic controlled purple nutsedge more effectively (10 plants/m2) than the fumigant-pebulate combinations (50 to 70 plants/m2). Compared to MBr plus Pic, Pic plus pebulate had a 14% lower marketable yield. No differences in marketable yield were noted with dazomet plus pebulate or C-17 plus pebulate compared to MBr plus Pic. However, MNa plus pebulate produced a 15% higher yield than MBr plus Pic. Additionally, MNa plus pebulate had 15% higher marketable fruit weight than MBr plus Pic.

Recent research at Mississippi State has shown that eastern gamagrass, switchgrass, and tall fescue grown as filter strips reduce herbicide losses in runoff from cotton. Field experiments were conducted in 1997 and 1998 to evaluate the response of these perennial grasses to postemergence drift and registered rates of glyphosate and paraquat in mid-April and clethodim, fluazifop-P, glyphosate, MSMA, pyrithiobac, quizalofop-P, and sethoxydim in early June. Results indicate that filter strip implementation will not simply involve establishment and maintenance. In most instances, reductions in harvested biomass were as high or higher than visual injury assessments in mid-June. This finding suggests an inability of these perennial grasses to recover from an accidental overspray or drift, within the year of the event. Management decisions must be made to protect the filter strips from contact with herbicides used in the production system to ensure filter strip integrity and survival.

Farmer observations and previous studies indicated that reductions in soybean yield caused by the soybean cyst nematode (SCN) are greater when other stresses, biotic or abiotic, are present. Also, it has been reported that the effect of SCN on soybean growth depended on factors such as soil pH, soil texture, and herbicides. Although postemergence herbicides may adversely affect soybean metabolism, acifluorfen can reduce SCN infection. The objective of the present study was to determine the main and interactive effects of SCN egg population density (SCND), soil pH, soil texture, and the application of the herbicides acifluorfen, glyphosate, and imazethapyr on early soybean growth. Greenhouse studies assessed different combinations of these factors for 65 d after planting. No interactions were observed for any of the main effects. Soil pH and texture did not affect soybean growth. SCND was the only main effect that explained soybean growth reductions. The effect of SCND on soybean growth was exhibited as 15–50% decreases of leaf area index (LAI) and dry weight in all cases, but reductions in plant height also were observed. No relationship between SCND and the number of SCN eggs recovered at the end of the experiment was observed. Herbicides did not reduce soybean growth, although acifluorfen consistently caused the highest soybean injury reaching 18–20% from 1–14 days after application (DAA). At 50 DAA, acifluorfen injury was negligible, and soybean LAI and dry weight did not differ from the nontreated control. These results indicated that the effect of SCN on soybean growth was not directly affected by the other evaluated main effects. Therefore, trends observed in the field that suggested interactions between those factors are likely the result of other factors not considered in the present study or to more complex relationships between factors analyzed in the present study and other elements present in the field.

Although dandelion has been recognized for some time as a common weed of perennial plant stands, recent weed surveys in western Canada indicate that dandelion has become more common in fields where annual spring crops are grown. Because little has been published on dandelion control in annual crops, a field study was conducted at two locations in southern Manitoba in 1999 and 2000 investigating the effect of spring tillage, glyphosate dosage, and application timing on dandelion control in a spring annual glyphosate-resistant canola crop. The experiments were situated in areas known to have natural infestations of dandelion. Final assessments of dandelion control were performed the spring following treatment, i.e., the next year, to provide a better indication of treatment efficacy on this perennial weed. Spring tillage alone did not significantly reduce dandelion density, as assessed the following spring, but did reduce dandelion shoot dry matter at three of the five site-years by up to 84%. Glyphosate was applied preplant, in-crop, and postharvest at dosages ranging from 450 g ae/ha in-crop to 2,700 g ae/ha postharvest. Glyphosate application after the canola crop had been harvested provided the greatest level of dandelion control, with a single postharvest application of 900 g ae/ha of glyphosate reducing dandelion density and shoot dry matter by 88 and 96%, respectively, the following spring. Applications of glyphosate either preplant or in-crop were not nearly as effective as the postharvest treatments in reducing dandelion density and shoot dry matter the following spring.

Field trials were conducted at five sites from 2001 through 2003 to determine the influence on sugarbeet and weeds of repeated broadcast and banded reduced rates of desmedipham plus phenmedipham, triflusulfuron, and clopyralid in combination with either 1.5 or 3% v/v methylated seed oil (MSO). Desmedipham plus phenmedipham, triflusulfuron, and clopyralid were applied POST three times at 5 to 7 d intervals at either 25, 50, 75, or 100% of a 180 plus 180 plus 18 plus 100 g ai/ha dosage (full rate). When averaged over all herbicide rates, crop injury was 6% greater, but common lambsquarters control was 5% higher, and crop yield was 15% greater with broadcast compared with banded herbicide application. In most situations, adding MSO at 3% rather than 1.5% did not improve weed control. Sugarbeet injury was lowest (11%) and the average weed control was 86% when herbicide rates (with 1.5% MSO) were 25% of the full rate (microrate). Applying an herbicide rate (with 1.5% MSO) that was 50% of the full rate (half rate) increased crop injury from 11% with the microrate to 18% with the half rate and elevated average weed control from 86% with the microrate to 92% with the half rate. Common lambsquarters control increased from 81% with the microrate to 89% with the half rate. Sugarbeet root yield was 23 t/ha when no herbicide was used, 48 t/ha with the microrate, and 49 t/ha with the half rate compared with 54 t/ha when the full rate was applied without MSO. Increasing herbicide rates to 75% of the full rate (three-quarter rate) (with 1.5% MSO) increased crop injury to 27% and average weed control to 96%. Applying 1.5% MSO to the full rate increased crop injury to 35% with no improvement in average weed control over that achieved with the full rate without MSO.

A study was conducted in 2000 and 2001 to evaluate interaction of fenoxaprop with other herbicides for barnyardgrass control in rice. Changes in herbicide interaction over time were also evaluated, and herbicide combinations were ranked on the basis of compatibility. Fenoxaprop at 0.075 kg/ha plus bentazon or propanil plus molinate resulted in an additive response for barnyardgrass control at 10, 20, and 30 d after treatment (DAT); however, when the rate of fenoxaprop increased to 0.089 kg/ha, an antagonistic effect was found. Carfentrazone and halosulfuron consistently antagonized the activity of fenoxaprop at both rates on barnyardgrass. Bensulfuron at 10 and 20 DAT and triclopyr at 20 DAT were antagonistic to fenoxaprop. An increase in interaction over time was detected when fenoxaprop at 0.089 kg/ha was applied in mixture with carfentrazone at 0.04 kg/ha or halosulfuron at 0.05 kg/ha. These results indicate that propanil plus molinate and bentazon are more compatible with fenoxaprop at 0.075 kg/ha for barnyardgrass control, whereas bensulfuron, carfentrazone, halosulfuron, and triclopyr can antagonize fenoxaprop activity on barnyardgrass.

Spray drift to unintended areas is more of a concern as applications of nonselective herbicides associated with herbicide-resistant crops and the proximity of residential land to agricultural land increase. This research evaluated the benefit of three commercial drift control agents for effectiveness in reducing drift in 19 to 24 km/h wind and their potential effect on weed control. The drift control agents were added to a spray mixture of glyphosate at 0.8 kg ae/ha applied in 140 L/ ha and applied with either flat-fan or flood nozzles. None of the drift control agents reduced drift compared with the spray mixture without drift control agent over a distance of 6 m, as measured by water-sensitive cards or grain sorghum bioassay, regardless of nozzle type used. In a separate study, drift control agents did not reduce the weed control of glyphosate or acifluorfen.

The impact of the management variables soybean cultivar, row spacing, population density, and shading was evaluated on the incidence of Sclerotinia stem rot (SSR) on glyphosate-resistant soybeans in an irrigated glyphosate-resistant soybean management system. Soybean canopy development, flower number, soil moisture, disease severity, and soybean yield were evaluated on three glyphosate-resistant cultivars, Pioneer ‘92B71’ (upright), Asgrow ‘AG2701’ (bushy), and Asgrow ‘AG2702’ (bushy). Three different row spacing–target population combinations of 76 cm, 430,000 seeds/ha; 19 cm, 430,000 seeds/ha; and 19 cm, 560,000 seeds/ha were evaluated. Cultivars 92B71 and AG2701 had 42 and 15% lower disease severity indexes and 38 and 19% greater yields than AG2702, respectively. The actual average population of 92B71 was 9 and 20% lower than actual average populations of AG2701 and AG2702, respectively. Disease severity indexes were lower and yield was higher when population was reduced from 560,000 seeds/ha to 430,000 seeds/ha in 19-cm rows. When averaged over the entire study, population was positively correlated with disease severity index (r2 = 0.33; P < 0.0001) and negatively correlated with yield (r2 = −0.13; P = 0.0140). Reduction of soybean population was more important than increasing row spacing to manage SSR in an irrigated system. Average actual spacing between plants within a row was 18 and 4 cm for 19- and 76-cm rows, respectively, at a target population of 430,000 seeds/ha, which may have contributed to greater plant-to-plant transfer of the Sclerotinia sclerotiorum pathogen in the 76-cm rows.

Sethoxydim, tralkoxydim, imazethapyr, quinclorac, propanil, glyphosate, and glufosinate were tested at rates below those recommended by the manufacturers with Pyricularia setariae Niskada under greenhouse conditions for control of green foxtail. At one-tenth of the recommended rate in a 100 L/ha carrier volume, only the sethoxydim–P. setariae combination achieved more effective green foxtail control when compared with the herbicide or pathogen alone. Selected herbicides at one-tenth, one-fourth, and one-half of the recommended rates showed variable interactions with the pathogen on plants with three and five leaves. Propanil (recommended rate 0.99 kg ai/ha) was more synergistic at higher rates, especially on larger plants, for which the combined treatment increased green foxtail mortality from zero in the herbicide alone to 100%. Quinclorac (recommended rate 0.10 kg ai/ha) acted similarly to propanil with slightly lower synergy effects. Sethoxydim (recommended rate 0.15 kg ai/ha) at one-tenth or one-quarter of the rate plus P. setariae often enhanced green foxtail control on larger plants. On smaller plants, the herbicide and pathogen alone were highly efficacious. Compared with tank mixes with P. setariae, propanil, quinclorac, or sethoxydim applied 6 h before the pathogen or earlier generally showed greater efficacy. Delaying a tank mix application for up to 2 h had little negative effect, but longer than 4 h often reduced efficacy. When combining the pathogen at different doses with propanil, quinclorac, or sethoxydim at one-tenth, one-quarter, and one-half of the rate, both fungal dose and herbicide rate affected the efficacy. Coapplying any of the herbicides at the one-quarter rate with the pathogen at the sublethal dose of 2 × 107 spores/ml achieved complete control of green foxtail.

Partial seed retention line #23(‘PSR23’) cuphea is a hybrid of Cuphea viscosissima × C. lanceolata. It is a new, spring-planted, annual, potential oilseed crop that is highly susceptible to interference by weeds because of its slow growth during spring and early summer. Grass weeds are controlled easily in this broadleaf crop, but broadleaf weeds are an appreciable problem. Consequently, several broadleaf herbicides were screened for tolerance by ‘PSR23’ cuphea. Broadleaf herbicides to which cuphea showed tolerance in a spray cabinet and a greenhouse were tested in a field setting for 2 yr. Field tolerance was considered as absence of negative impact (P > 0.05) both years to any of four measured traits: overall vigor, dry weight, stand density, and time to anthesis. Cuphea showed tolerance in the field to three soil-applied herbicides (ethalfluralin, isoxaflutole, and trifluralin) and one postemergence herbicide (mesotrione). A few combinations of soil-applied and postemergence herbicides did not damage cuphea. These combinations were ethalfluralin followed by (fb) mesotrione, isoxaflutole fb imazethapyr, and isoxaflutole fb mesotrione. Availability of these herbicides for use in cuphea production may facilitate the domestication and acceptance of this new crop.

The importance of spray retention to the biocontrol of green foxtail with Pyricularia setariae was characterized using airbrush and broadcast sprayers at variable application volumes. Spray retention was determined by measuring amounts of a tracer dye solution on treated plants using fluorescence spectrophotometry. Depending on the droplet size, broadcast spraying at 1,000 to 2,000 L/ha produced a level of retention equivalent to that of airbrush spraying until runoff. The trend of P. setariae spore retention on green foxtail was similar to that of liquid retention. Broadcasting P. setariae at volumes producing equivalent spray retention to that of airbrush inoculation resulted in a similar level of weed control under greenhouse conditions. Reducing broadcast volume from 2,000 to 250 L/ha lowered biocontrol efficacy only slightly, when the concentration of P. setariae was increased proportionally to keep the applied fungal dose the same. A nozzle with a fine droplet spectrum (volume median diameter [VMD] 207 μm) had a significantly greater retention efficiency than a coarse spray (VMD 325 μm), but this retention difference was not translated into consistent enhancement of biocontrol efficacy. Higher retention increases may be necessary for more substantial improvement in biocontrol of green foxtail by P. setariae.

Weed-wipers may provide effective weed control while minimizing the application of herbicide to nontarget species in rangeland and pasture. To date, few herbicides are recommended for use in weed wiping systems. We assessed Canada thistle and non–Canada thistle herbage responses in two experiments in pastures, the first examining wiped glyphosate, the second comparing glyphosate with three broadleaf herbicides at cost-equivalent concentrations [on a volume to volume (v/v) dilution basis]. In both studies, wiping with a glyphosate solution (33% v/v, equivalent to a one to two dilution ratio of herbicide to water) resulted in lower Canada thistle density and biomass than check plots, with control lasting up to 2 yr. However, significant reductions in grass biomass also occurred and were associated with an increase in the abundance of weedy annual forbs. In contrast, wiping with a concentrated solution of clopyralid (2% v/v), picloram plus 2,4-D (20% v/ v), or 2,4-D plus mecoprop plus dicamba (24% v/v), resulted in similar levels of Canada thistle control but no reduction in grass biomass. Despite direct application of herbicides to tall weeds, clover species in mixed stands were injured. In grass-dominated pastures, wiping with broadleaf herbicides was superior to nonselective glyphosate because the former more effectively balanced Canada thistle control with the retention of grass production.

KIH-485 is an experimental herbicide being evaluated for preemergence weed control in corn. Field experiments were conducted in Burleson County, Texas, in 2003 and 2004 to compare weed control, corn tolerance, and corn yield with various rates of KIH-485 or S-metolachlor. Each herbicide was applied in single preemergence applications at four rates, or in combination with atrazine. KIH-485 at 500 g ai/ha provided better Texas panicum control than S-metolachlor by 9 WAT. KIH-485 or S-metolachlor treatments controlled Palmer amaranth at least 91% at all evaluation dates. In 2003, no other treatment controlled velvetleaf better than 500 g/ha KIH-485. The following year, all KIH-485 rates above 125 g/ha controlled velvetleaf better than any rate of S-metolachlor alone. Moreover, KIH-485 controlled all weed species as good as or better than S-metolachlor plus atrazine, regardless of KIH-485 rate. There was no significant corn injury observed, and grain yield reflected the effects of weed control.

Irrigated field experiments were conducted near Torrington, WY, during the 2001 to 2002 (year 1) and 2002 to 2003 (year 2) winter wheat growing seasons to evaluate cultivar response to different imazamox rates, adjuvants, and application timings. Five cultivars were treated postemergence in the early fall (EF), late fall (LF), or early spring (ES) with imazamox at 54 or 108 g ai/ha, including either nonionic surfactant (NIS) at 0.25% or methylated seed oil (MSO) at 1% (v/v) as adjuvants. A 28% urea ammonium nitrate solution at 1% (v/v) was included with all treatments. Spring injury was more severe in year 1 than year 2. Severe spring injury on ‘AP502 CL’, ‘Above’, ‘IMI-Fidel’, ‘IMI-Jagger’, and ‘IMI-Madsen’ was linked to fall application of 108 g/ha imazamox with MSO. Imazamox applied at 108 g/ha plus MSO applied in the fall consistently injured all cultivars more than the same rate with NIS and 54 g/ha imazamox regardless of adjuvant and timing, although severity of injury in the experiments differed between EF and LF timings in years 1 and 2, respectively. Correlation analysis supports injury reduced reproductive tillers per meter of row and wheat yields and increased the number of seeds per spike in year 1. The reduction of reproductive tillers per meter of row in year 1 was likely the result of severe injury caused by 108 g/ha imazamox applied in the EF coupled with little snow cover to protect against cold winter temperatures. Wheat yield in year 1 was reduced by 108 g/ha imazamox applied in the early fall; however, imazamox applied at 54 g/ha with either adjuvant in EF, LF, or ES were safe. Yield parameters and wheat yields in year 2 were not affected by imazamox rate, adjuvant, timing, or interactions of these factors.

Yellow starthistle is an aggressive annual forb that has invaded millions of hectares of California's annual range. Control efforts such as burning and herbicides have been effective for short-term management. However, recruitment from the seedbank or reinvasion of the annual grassland system results in a rapid return to yellow starthistle dominance. Establishing perennial grasses would be ideal for suppression of yellow starthistle. However, a lack of effective weed control options in California during a seeding program has limited perennial grass establishment. Clopyralid was used to control yellow starthistle annually for 1, 2, or 3 yr to provide a window of reduced competition for pubescent wheatgrass establishment. Total plant cover, yellow starthistle density, biomass, and seedhead number were quantified for 6 yr. Clopyralid treatment significantly reduced yellow starthistle and allowed pubescent wheatgrass establishment with a single treatment. Both clopyralid treatment and pubescent wheatgrass establishment significantly affected the range plant community composition. Annual grasses and forbs increased in plots only treated with clopyralid for 2 or 3 yr, whereas clopyralid-treated pubescent wheatgrass plots maintained lower annual grass and forb cover. Integrating pubescent wheatgrass seeding with clopyralid treatment provided long-term yellow starthistle suppression, whereas clopyralid treatment alone resulted in a plant community susceptible to repeated invasion. These findings support the establishment of competitive perennial grasses in annual grasslands as an important component of long-term yellow starthistle management.

A study was conducted in 2002 and 2003 to evaluate response of seven rice cultivars to V-10029 applied at 20 and 40 g ai/ha to two- to three- or four- to five-leaf rice. Differential response of the rice cultivars to V-10029 was observed. Medium-grain ‘Earl’ was less tolerant to V-10029, as reflected by increased injury, shorter plants, and fewer plants at 7 d after late postemergence treatment and shorter plants and lower grain yield at harvest, when compared with nontreated Earl. Growth of medium-grain ‘Bengal’ was initially inhibited by V-10029; however, plant height at harvest and rice grain yield of Bengal were not affected. All long-grain cultivars exhibited tolerance to V-10029, both initially and at harvest. The results indicate that rice cultivars vary in tolerance to V-10029.

A 2-yr experiment repeated at five locations across the northeastern United States evaluated the effect of weed density and time of glyphosate application on weed control and corn grain yield using a single postemergence (POST) application. Three weed densities, designed to reduce corn yields by 10, 25, and 50%, were established across the locations, using forage sorghum as a surrogate weed. At each weed density, a single application of glyphosate at 1.12 kg ai/ha was applied to glyphosate-resistant corn at the V2, V4, V6, and V8 growth stages. At low and medium weed densities, the V4 through V8 applications provided nearly complete weed control and yields equivalent to the weed-free treatment. Weed biomass and the potential for weed seed production from subsequent weed emergence made the V2 timing less effective. At high weed densities, the V4 followed by the V6 timing provided the most effective weed control, while maintaining corn yield. Weed competition from subsequent weed emergence in the V2 application and the duration of weed competition in the V8 timing reduced yield on average by 12 and 15%, respectively. This research shows that single POST applications can be successful but weed density and herbicide timing are key elements.

Field violet is a winter or summer annual plant that is a serious weed of canola crops in Europe. It is a weed of increasing concern within reduced tillage fields in central Alberta, where its response to registered herbicides has not been evaluated. Two commercial fields within the Aspen Parkland ecoregion of Alberta were used to evaluate the efficacy of postemergence (POST) herbicides against field violet in conventional, imidazolinone-resistant (IMI-resistant) and glufosinate-resistant canola cultivars, as well as to evaluate the plant's response to various timings and rates of glyphosate in glyphosate-resistant canola. Control of field violet was lower in field experiments conducted in 2002 compared with 2003, probably because of abnormally low rainfall in 2002. The POST herbicides evaluated provided inadequate control of field violet in conventional canola. Glufosinate control at 500 g ai/ha was unacceptable unless the crop canopy closed shortly after application. In IMI-resistant canola, thifensulfuron did not significantly reduce plant density and biomass under the extremely dry conditions experienced in 2002, but in 2003, it conferred respective reductions of 79 and 86% relative to nontreated controls. Imazamox plus imazethapyr did not affect plant growth. Field violet was controlled by pre- and postcrop emergence glyphosate at 445 g ae/ha. Postharvest application of glyphosate provided good control throughout the following growing season when spring emergence was minimal. Herbicide activity was also evaluated on two- to four-leaf seedlings in a greenhouse experiment. Dose– response curves reflected the activity observed in field experiments. Strategies for effective field violet control with herbicides are dependent on cultivar selection and the management system, but are improved by timing application to young, actively growing plants.

Field studies were conducted near Marianna, FL during 1999 and 2000 to evaluate weed control and peanut response to PPI treatments of diclosulam alone, PRE treatments of flumioxazin alone, and in systems with POST commercial standard herbicides. Diclosulam and flumioxazin alone did not control sicklepod. Paraquat plus bentazon plus 2,4-DB applied early POST fb chlorimuron plus 2,4-DB or imazapic controlled sicklepod and pitted morningglory at least 83%. These treatments were equal to or greater than diclosulam or flumioxazin with or without paraquat plus bentazon plus 2,4-DB, or the same system fb 2,4-DB mid POST. Peanut yield was similar when treated with diclosulam or flumioxazin fb the standard early POST (EPOST) system, flumioxazin alone, or imazapic alone. Peanut treated with diclosulam alone or paraquat plus bentazon plus 2,4-DB fb 2,4-DB yielded lower than other treatments because of late-emerging Florida beggarweed. Peanut treated with chlorimuron, regardless of which soil-applied herbicide was used, yielded less due to a longer period of interference from Florida beggarweed, sicklepod, and pitted morningglory because of the timing of chlorimuron application (60 d after planting).

Field experiments were conducted to evaluate the influence of preemergence (PRE) herbicides metolachlor at 1,700 g ai/ha, pyrithiobac at 70 g ai/ha, or pendimethalin at 840 g ai/ha applied alone or with fluometuron at 1,300 g ai/ha and glyphosate postemergence (POST) at 840 g ai/ha on seedling diseases in glyphosate-resistant cotton. Hypocotyl disease severity both years averaged across PRE herbicide treatments was greater after glyphosate application to four-leaf cotton than cotyledon cotton. The PRE herbicide treatments, particularly those including fluometuron, increased root and hypocotyl disease ratings compared with a nontreated control, and a sequential application of glyphosate did not further increase disease severity. Greenhouse experiments using soil infested with Rhizoctonia solani confirmed findings from the field study showing that PRE herbicides can predispose cotton to greater seedling disease injury with no increased seedling disease severity associated with application of glyphosate. In the field study, glyphosate applied at cotyledon or four-leaf growth stages decreased disease severity on cotton hypocotyls both years. This inhibitory effect of glyphosate was less evident in the greenhouse study and may have been related to species of fungi present, infestation level, and differences in environmental conditions when compared with the field.