Field studies were conducted in 2011 and 2012 at the Horticultural Crops Research Station near Clinton, NC, to determine ‘Covington' sweetpotato tolerance to S-metolachlor rate and application timing. Treatments were a factorial arrangement of four S-metolachlor rates (0, 1.1, 2.2, or 3.4 kg ai ha−1) and six application timings (0, 2, 5, 7, 9, or 14 d after transplanting [DAP]). Immediately following application, 1.9 cm of irrigation was applied to individual plots. Sweetpotato injury was minimal for all treatments (≤ 10%). No. 1 grade sweetpotato yield displayed a negative linear response to S-metolachlor rate, and decreased from 25,110 to 20,100 kg ha−1 as S-metolachlor rate increased from 0 to 3.4 kg ha−1. Conversely, no. 1 sweetpotato yield displayed a positive linear response to S-metolachlor application timing and increased from 19,670 to 27,090 kg ha−1 as timing progressed from 0 to 14 DAP. Total marketable sweetpotato yield displayed a quadratic response to both S-metolachlor application rate and timing. Total marketable yield decreased from 44,950 to 30,690 kg ha−1 as S-metolachlor rate increased from 0 to 3.4 kg ha−1. Total marketable yield increased from 37,800 to 45,780 kg ha−1 as application timing was delayed from 0 to 14 DAP. At 1.1 kg ha−1S-metolachlor, sweetpotato storage root length to width ratio displayed a quadratic relationship to application timing and increased from 1.87 to 2.23 for applications made 0 to 14 DAP. At 2.2 kg ha−1 of S-metolachlor, sweetpotato length to width ratio displayed a quadratic response to application timing, increased from 1.57 to 2.09 for 0 to 10 DAP, and decreased slightly from 2.09 to 2.03 for 10 to 14 DAP. Application timing did not influence length to width ratio of sweetpotato storage roots for those plots treated with S-metolachlor at either 0 or 3.4 kg ha−1.

Herbicides are an important tool in managing weeds in turf and agricultural production. One of the earliest selective herbicides, 2,4-D, is a weak acid herbicide used to control broadleaf weeds. Water-quality parameters, such as pH and hardness, influence the efficacy of weak acid herbicides. Greenhouse experiments were conducted to evaluate how varying water hardness level, spray solution storage time, and adjuvant inclusion affected broadleaf weed control by 2,4-D dimethylamine. The first experiment evaluated a range of water-hardness levels (from 0 to 600 mg calcium carbonate [CaCO3] L−1) on efficacy of 2,4-D dimethylamine applied at 1.60 kg ae ha−1 for dandelion and horseweed control. A second experiment evaluated dandelion control from spray solutions prepared 0, 1, 4, 24, and 72 h before application. Dandelion and horseweed control by 2,4-D dimethylamine was reduced when the CaCO3 level in water was at least 422 or at least 390 mg L−1, respectively. Hard-water antagonism was overcome by the addition of 20 g L−1 ammonium sulfate (AMS) into the mixture. When AMS was included in spray mixtures, no differences were observed at 600 mg CaCO3 L−1, compared with distilled water. Spray solution storage time did not influence dandelion control, regardless of water-hardness level or adjuvant inclusion. To prevent antagonism, applicators should use a water-conditioning agent such as AMS when applying 2,4-D dimethylamine in hard water.

Rattail fescue infestations are increasing in dryland conservation-tillage winter wheat cropping systems in the inland Pacific Northwest (PNW) region of Idaho, Oregon, and Washington. Rattail fescue typically is controlled with cultivation in conventional tillage farming systems. However, reduced soil disturbance has allowed infestations to increase significantly. The objectives of this research were to determine the effectiveness of glyphosate rates and application timings on control of rattail fescue during a chemical-fallow period in winter wheat cropping systems. Chemical-fallow field studies were conducted during two growing seasons at nine sites throughout the PNW. Glyphosate was applied early POST, late POST, or sequentially in early plus late POST timings. Additionally, paraquat + diuron was applied early and late POST alone or sequentially with glyphosate. Sequential application treatments (glyphosate followed by [fb] glyphosate, paraquat + diuron fb glyphosate, and glyphosate fb paraquat + diuron) controlled rattail fescue (∼ 94% in Idaho and Washington, ∼ 74% in Oregon) and reduced panicle number (∼ 85% in Idaho, ∼ 30% in Oregon and Washington) equivalent to or greater than one-time treatments. Rattail fescue control and panicle reduction generally increased with increasing rates of glyphosate within application timings. Paraquat + diuron usually provided similar control and reduced rattail fescue panicle number compared to glyphosate treatments applied at the same application timing. Although not completely effective, sequential applications of either glyphosate or paraquat + diuron, fb glyphosate will provide effective control during chemical fallow.

BAS-145-138 considerably muted the herbicidal effect of the sulfonylurea herbicides on corn. Decreases of 54 and 52% in shoot fresh and dry weight caused by 10 μM chlorsulfuron were countered almost completely by 1.5 mM BAS-145-138 with only a 10% loss in fresh weight and a 3% loss in dry weight. Similar strong antidotal influence by BAS-145-138 on chlorimuron was observed. BAS-145-138 partially protected corn against sulfometuron. Shoot fresh weight of corn treated with 0.2 μM sulfometuron was inhibited 88%, whereas adding 0.5 or 1.5 mM BAS-145-138 reduced inhibition to 52 and 24%, respectively.

Experiments were conducted on Sharkey clay and Gigger silt loam soils in northeast Louisiana from 1990 through 1993 to compare season-long barnyardgrass control, rice yield, and estimated economic returns with single and multiple applications of propanil alone or with molinate or thiobencarb. Multiple herbicide applications were more effective than single applications in controlling barnyardgrass and provided the greatest rice yields and economic returns. Applying residual herbicides with propanil improved barnyardgrass control in five of six experiments and increased rice yield and economic returns in three of six experiments.

Vapor movement of synthetic auxin herbicides can injure desirable plants outside the treatment zone. Vapor movement of the synthetic auxin herbicides aminocyclopyrachlor and aminocyclopyrachlor methyl was compared with that of the relatively volatile herbicide dicamba and the low volatile herbicide aminopyralid with a soybean bioassay under greenhouse and field conditions. Soybean is very sensitive to these active ingredients. Under greenhouse conditions, 82 (61 to 104) mg ae ha−1 of aminocyclopyrachlor, 26 (18 to 33) mg ae ha−1 of aminocyclopyrachlor methyl, 82 (69 to 95) mg ae ha−1 of aminopyralid, and 61 (47 to 75) mg ae ha−1 of dicamba produced an estimated 25% visual soybean phytotoxicity response when soybean was treated POST at the V3 growth stage (GR25 [95% confidence interval]). In field studies, aminocyclopyrachlor, aminocyclopyrachlor methyl, and aminopyralid were applied at 70 g ae ha−1 and dicamba was applied at 560 g ae ha−1 (labeled application rates) to soybean at the V3 growth stage. All herbicides were applied within an enclosed chamber (3 m by 3 m by 1 m) to mitigate movement of spray droplets. The enclosures were removed shortly after spray application and soybean response immediately surrounding the treated area was recorded in each of eight directions approximately 10 d after treatment. On the basis of bioassay responses, relative amount of vapor movement was dicamba > aminocyclopyrachlor methyl > aminopyralid ≈ aminocyclopyrachlor. Vapor movement of aminocyclopyrachlor was very low indicating that the risk of phytotoxic response of sensitive plants due to volatility of aminocyclopyrachlor is negligible.

Field trials were conducted in the spring of 2004 and the spring and summer of 2005 to evaluate cantaloupe tolerance to rimsulfuron and halosulfuron applied to cantaloupe at the two-leaf stage, five- to six-leaf stage, plants having 30- to 40-cm vines, and plants having up to 5-cm-diam melons. Additionally, control of eight weed species was evaluated in these trials in 2005. Cantaloupe plant injury from rimsulfuron differed among application timings and trials, but applications were generally more injurious when applied at the two early crop stages. Halosulfuron was less injurious to cantaloupe, but 31 and 14% injury occurred following the two-leaf and five- to six-leaf applications, respectively, in the second trial in 2005. In the first trial of 2005, number of marketable melons the first week of harvest was lower for all halosulfuron applications compared with the nontreated control (30 to 37% reduction). In the second trial of 2005, total number of marketable melons was comparable to the nontreated control for each of the halosulfuron treatments, except the five- to six-leaf and up to 5-cm-diam melon applications. Injury estimates were poor indicators of occurrence or absence of delays in crop earliness or number of marketable melons. Rimsulfuron was generally effective (≥ 80% control) in controlling seedling Texas panicum, large crabgrass, tall morningglory, pitted morningglory, and Palmer amaranth, but was ineffective against yellow and purple nutsedge and goosegrass. Halosulfuron was effective in controlling yellow and purple nutsedge, but was ineffective against Texas panicum, large crabgrass, goosegrass, pitted morningglory, tall morningglory, and Palmer amaranth.

Persistence of microencapsulated (ME) and emulsifiable concentrate (EC) formulations of alachlor and acetochlor, as well as EC formulations of metolachlor, s-metolachlor, dimethenamid, and flufenacet were studied using a bioassay based on root response of oat Kassandra grown in soil. Flufenacet was the most persistent of the herbicides, but biologically available residues were not detected at 0- to 10-cm soil depth 50 d after any herbicide treatment. All herbicides applied preemergence (PRE) in field trials gave good to excellent control of redroot pigweed, black nightshade, barnyardgrass, and green foxtail but only partial control of jimsonweed. Furthermore, when they were applied postemergence (POST) in mixture with atrazine in the field, the control obtained for black nightshade, common lambsquarters, common purslane, and redroot pigweed was excellent, but good to excellent for bristly foxtail and green foxtail. Their efficacy against yellow foxtail and large crabgrass was fair to good. Generally, the EC-alachlor and EC-acetochlor applied POST in mixture with atrazine gave better control of grasses than did their ME-formulations. None of the herbicide treatments showed any phytotoxic effect on corn, and all of them produced corn yield greater than that of weedy control but slightly lower than that of the weed-free control. Flufenacet, s-metolachlor, and dimethenamid were suitable alternatives to acetochlor, alachlor, and metolachlor.

Studies were conducted to evaluate preplant incorporated (PPI), preemergence (PRE), and postemergence (POE) herbicide treatments on yellow nutsedge control and on growth and yield of transplanted onions. Most effective yellow nutsedge control (≥80%) was achieved with metolachlor applied PPI plus PRE. Metolachlor and SAN 582H were more effective applied PPI than PRE. Bentazon alone applied POE adequately controlled yellow nutsedge only 1 of 2 yr. Highest onion yields and percent jumbo bulbs were produced when treatments included metolachlor applied PPI.

The effectiveness of single and repeated annual preharvest glyphosate applications (1 to 2 wk before crop harvest) to reduce Canada thistle populations was evaluated in field experiments near Bezanson, AB, Scott, SK, and St. Albert, AB. Single applications of glyphosate at 0.45 to 1.8 kg/ha at Bezanson and St. Albert reduced Canada thistle shoot density by more than 75% but in the three experiments at Scott 1.8 kg/ha was required to consistently obtain a similar reduction. Four consecutive, annual applications of glyphosate at 0.45 kg/ha or more did not eliminate Canada thistle but reduced shoot densities by more than 98% at Bezanson. At Scott, similar reductions occurred in two of three sites following two consecutive, annual preharvest applications of glyphosate at the same rates. In the third Scott site the 1.8 kg/ha rate of glyphosate provided a similar reduction but lower rates did not. At Bezanson, barley yields following the first, second, and third applications of glyphosate at 0.45 kg/ha or more were 14% greater than check plots where MCPA was applied in the spring. Yields of wheat seeded 1 yr after a single application of glyphosate at St. Albert were 26% greater than from unsprayed checks. Barley yields seeded 1 yr after each glyphosate application at Scott were not affected because Canada thistle populations were sparse.

Field experiments were conducted to examine the effect of tillage on atrazine [6-chloro-N-ethyl-N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine] persistence in the soil and soybean [Glycine max (L.) Merr.] injury. Tillage systems evaluated were no-tillage, chisel plowing, and moldboard plowing. Reduced tillage systems, such as no-tillage or chisel plowing, resulted in greater soybean injury from atrazine residue than did moldboard plowing. Regardless of atrazine residue level, metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one] resulted in the greatest injury to soybeans. Metribuzin application in combination with atrazine residue increased soybean injury under the chisel plowed system.

Studies were conducted at Rosemount and Crookston, MN, in 1994 and 1995 to determine weed control efficacy and crop injury of F8426 (proposed common name carfentrazone-ethyl) in hard red spring wheat. F8426 alone and with 2,4-D or dicamba generally controlled common lambsquarters, kochia, and velvetleaf 90% or more at 0.026 and 0.035 kg/ha. F8426 alone and with 2,4-D or dicamba controlled Pennsylvania smartweed, wild buckwheat, and wild mustard 39 to 100% and was less consistent than control of the aforementioned species. Weed control varied little among the F8426 rates. Weed control was inconsistent between location, year, and species when F8426 was combined with crop oil concentrate, urea–ammonium nitrate solution, and nonionic surfactant. Control was more consistent when 0.28 kg/ha 2,4-D or 0.07 kg/ha dicamba was tank mixed with either F8426 rate. The best control with an F8426 treatment was similar to control from MCPA tank mixed with thifensulfuron plus tribenuron, bromoxynil, or dicamba. Weed control 30 and 45 days after treatment (DAT) was less for F8426-containing treatments than standard treatments, which likely was related to reduced crop competition after severe crop injury. Increasing F8426 rate from 0.026 to 0.035 kg/ha did not greatly increase wheat injury, whereas adding 0.28 kg/ha 2,4-D to either F8426 rate greatly increased crop injury. Wheat yield was reduced up to 63% by F8426 and 2,4-D combinations.

MKH 6562 is a new acetolactate synthase inhibitor herbicide that would provide an alternative to control wild oat. Three experiments were conducted at Scott, SK, Canada, from 1996 to 1999 to evaluate MKH 6562 rates (20 and 30 g ai/ha), carrier volumes (30, 50, and 100 L/ha), time of applications (two- to three-leaf and three- to four-leaf stages of wild oat), and broadleaf weed herbicide tank mixtures. Reduced wild oat control (lower visual rating of percent control and higher fresh weight) often occurred when MKH 6562 was applied at a rate of 20 vs. 30 g/ha, with carrier volumes of 30 vs. 50 and 100 L/ha, and at the three- to four-leaf vs. two- to three-leaf stages of wild oat. Wild oat control generally was lower for MKH 6562 tank mixed with dicamba + mecoprop + MCPA 1:1:4.4 and bromoxynil + MCPA 1:1 compared with MKH 6562 applied alone or tank mixed with other broadleaf herbicides. MKH 6562 tank mixed with MCPA, and to a lesser extent 2,4-D, resulted in decreased wild oat control when applied at the three- to four-leaf stage of wild oat, but not at the two- to three-leaf stage. Wheat grain yield usually was not affected by MKH 6562 rate and carrier volume. Yield was 7% lower when MKH 6562 was tank mixed with dicamba + mecoprop + MCPA or fluroxypyr + 2,4-D and was 8% lower when MKH 6562 was applied in a mixture with 2,4-D formulations or bromoxynil + MCPA at the three- to four-leaf stage compared with the two- to three-leaf stage. Similar yields were achieved when MKH 6562 was applied alone at both leaf stages of wild oat. Wild oat control and wheat yield with MKH 6562 were as good as or better than with ICIA 0604 and imazamethabenz and were as good as or poorer than with CGA 184927. MKH 6562 provides adequate control of wild oat in wheat when applied early with the recommended carrier volume. Satisfactory control may be achieved with reduced rates if wild oat infestations are light.

Field studies were conducted in 1992 and 1993 to evaluate AC 263,222 applied postemergence (POST) alone and as a mixture with atrazine or bentazon for weed control in imidazolinone-resistant corn. Nicosulfuron alone and nicosulfuron plus atrazine were also evaluated. Herbicide treatments were applied following surface-banded applications of two insecticides, carbofuran or terbufos at planting. Crop sensitivity to POST herbicides, corn yield, and weed control was not affected by insecticide treatments. AC 263,222 at 36 and 72 g ai/ha controlled rhizomatous johnsongrass 88 and 99%, respectively, which was equivalent to nicosulfuron applied alone or with atrazine. AC 263,222 at 72 g/ha controlled large crabgrass 99% and redroot pigweed 100%, and this level of control exceeded that obtained with nicosulfuron alone. AC 263,222 at 72 g/ha controlled sicklepod and morningglory species 99 and 98%, respectively. Nicosulfuron alone or with atrazine controlled these two species less than AC 263,222 at 72 g/ha. Addition of bentazon or atrazine to AC 263,222 did not improve control of any species compared with the higher rate of AC 263,222 at 72 g/ha applied alone. Corn yield increased over the untreated control when POST herbicide(s) were applied, but there were no differences in yield among herbicide treatments.

Field studies were conducted in South Carolina and Georgia to evaluate weed control and soybean tolerance and yield after nonionic surfactant addition to combinations of chlorimuron plus an adjuvant-containing glyphosate formulation. Treatments included glyphosate alone, at 420 or 840 g ae/ha, or in combination with 6 or 9 g ai/ha chlorimuron and all possible combinations with or without 0.25% (v/v) nonionic surfactant. Other treatments included a weed-free and nontreated check. Chlorimuron plus glyphosate improved entireleaf, smallflower, and tall morningglory control over glyphosate alone, but nonionic surfactant addition did not further improve the control of any species, except tall morningglory. Up to 31% early-season injury was observed with the three-way mixture. Soybean injury was greater, and yields were reduced in one of three trials when nonionic surfactant was added to chlorimuron plus glyphosate combinations. This research indicates that there would be no benefit from the nonionic surfactant addition to this adjuvant-containing glyphosate formulation when combined with chlorimuron.

Decision support systems (DSSs) have been developed to assist producers and consultants with weed management decisions. WeedSOFT is a DSS currently used in several states in the north-central region of the United States. Accurate estimates of crop yield loss due to weed interference are required for cost-effective weed management recommendations. WeedSOFT uses competitive indices (CIs) to predict crop yield loss under multiple weed species, weed densities, and relative times of weed emergence. Performance of several WeedSOFT versions to predict soybean yield loss from weed competition was evaluated using CI values in WeedSOFT version 9.0 compared to new CI values calculated from weed dry matter, weed volume, and soybean yield loss in two soybean row spacings (19 and 76 cm) and two relative weed emergence times (at soybean emergence and first trifoliate leaf stage). Overall, new CI values improved predictions of soybean yield loss by as high as 63%. It was especially true with using new CI values based on yield loss compared to those based on weed dry matter or weed volume. However, there were inconsistencies in predictions for most weed species, suggesting that additional modifications are needed to further improve soybean yield loss predictions.

Field studies were conducted near Painter, VA, in 1995 and 1996 to investigate the effects of herbicides and cultivation on weed control, yield, and net returns in potato. Potato injury from herbicides and/or cultivation was not observed in 1995 and was less than 12% in 1996. Metribuzin plus metolachlor preemergence controlled yellow nutsedge by at least 81% regardless of the number of cultivations in 1995 and 1996. Yellow nutsedge control with metribuzin plus rimsulfuron postemergence (POST) plus three cultivations was as high as 70% in 1995 and 88% in 1996. Metribuzin plus rimsulfuron POST controlled common lambsquarters by at least 95% and common ragweed by at least 83% regardless of the number of cultivations in 1995 and 1996. A-size tuber production and net returns from potato receiving herbicides were not improved with two or three cultivations in 1995 or 1996. However, when averaged over all weed control systems (herbicide and cultivation-only systems) multiple cultivations significantly increased control of all weed species, A-size tuber production, and net returns.

Herbicides commonly used to control Cyperus spp. are not completely effective against Kyllinga spp. Field trials were conducted on North Carolina golf courses to evaluate green and false-green kyllinga control at fairway and rough golf course mowing heights. Treatments included single and sequential applications of bentazon (1.12 kg ai/ha), halosulfuron (0.07 kg/ha), MSMA (2.24 kg/ ha), and trifloxysulfuron (0.03 kg/ha); imazaquin (0.56 kg/ha) with and without MSMA; and two rates of sulfentrazone (0.42 and 0.56 kg/ha). Green or false-green kyllinga control was equivalent at fairway and rough mowing heights. Halosulfuron applied sequentially, imazaquin with and without MSMA, and trifloxysulfuron applied singly or sequentially, controlled green and false-green kyllinga 89 to 99% 10 wk after initial treatment (WAIT). However, Kyllinga spp. control decreased over the course of the study regardless of herbicide treatment. By one year after treatment (YAIT), bentazon or MSMA alone controlled green or false-green kyllinga 50% or less. No difference was observed in green or false-green kyllinga control between imazaquin vs. imazaquin plus MSMA, sulfentrazone 0.42 vs. 0.56 kg/ha, or trifloxysulfuron one vs. two applications at any rating date. Green kyllinga was seemingly more difficult to control than false-green kyllinga. Sequential applications of bentazon and MSMA, single applications of halosulfuron, sulfentrazone applied at 0.42 and 0.56 kg/ha, and single and sequential applications of trifloxysulfuron controlled false-green kyllinga at least 10% greater than green kyllinga at 1 YAIT. Further research is needed to assess the potential variation among Cyperus and Kyllinga spp. response to herbicides.

Weed control was evaluated in no-till planted soybean in both burned and standing wheat stubble for 3 yr. High, intermediate, low, and no weed management following no-till planting of soybean were compared with a tilled treatment with high weed management. Herbicides for the high weed management were metribuzin plus metolachlor PRE followed by POST applications, as needed, of bentazon, acifluorfen, and fluazifop or quizalofop. Intermediate management included all of the above except metolachlor, plus the as-needed use of chlorimuron or lactofen POST. Low management had no PRE herbicide applications but included the above POST herbicides. Glyphosate was used as a preplant foliar applied desiccant in the stubble-planted soybean of all weed management levels. Yield of soybean was not affected by standing, burned, or tilled wheat stubble. Soil organic matter in the 0 to 2.5 cm of soil was not significantly affected at the end of the 3 yr. Yield of wheat was reduced by standing wheat stubble in the first year of the study. Total POST weed control was sufficient for maximum soybean yields in the second and third years of the study. The weed spectrum changed during the experiment for the no-weed-control treatment in soybean and in wheat. The major weeds present in soybean after 3 yr of no-till were southern crabgrass, nodding spurge, redvine, prickly sida, barnyardgrass, and johnsongrass; in wheat they were Italian ryegrass, little barley, mayweed chamomile, and hairy buttercup.

Field experiments were conducted in 1987 and 1988 to examine interference from a natural population of perennial sowthistle on soybean and dry edible bean. In 1987, an average of 78 and 90 perennial sowthistle shoots per m2 in 71-cm (wide) crop row spacing reduced soybean and dry edible bean yield by 49% and 36%, respectively. In 1988, a year of less precipitation, an average density of 96 and 88 shoots per m2 reduced soybean and dry bean yield by 87% and 83%, respectively. One cultivation 5 wk after planting increased crop yield and decreased perennial sowthistle density compared with no cultivation. Perennial sowthistle reduced seed weight, germination percentage, and seedling growth rate of seed produced by both crops. In the presence of perennial sowthistle, one cultivation resulted in improved seed quality compared with no cultivation.