Cogongrass is commonly found in disturbed areas in Florida, where it is increasingly becoming a problem in bahiagrass pastures. Soil pH has been suggested as a possible mechanism for this invasion; to evaluate this, replacement series competition studies were conducted under greenhouse conditions at two soil pH levels: pH 4.5, or pH 6.8. Cogongrass ramets and bahiagrass seedlings were planted at proportions of 0:40, 1:20, 2:10, 4:1, and 8:0, respectively. Aboveground biomass was measured after 8 weeks and used to calculate relative yield, relative crowding coefficients, and aggressivity values. At soil pH 4.5, the relative competitiveness of cogongrass and bahiagrass was similar, with both species contributing equally to relative yield. At soil pH 6.8, bahiagrass seedlings showed greater competitive ability than cogongrass ramets. Relative crowding coefficient and aggressivity values supported this, with bahiagrass showing increased competitiveness under higher soil pH. This indicates that decreases in soil pH, often associated with poor soil fertility, is likely a contributing factor for cogongrass invasion into bahiagrass pastures. Soil amendments to raise pH may provide a cultural management tool for cogongrass infestations in pastures.

Tiafenacil is a new nonselective, protoporphyrinogen IX oxidase–inhibiting pyrimidinedione herbicide that is under consideration for registration to control grass and broadleaf weeds in corn, soybean, wheat, cotton, and other crops prior to crop emergence. The sensitivity of dry beans to tiafenacil is not known. Four field experiments were completed at Exeter and Ridgetown, ON, Canada, during the 2019 and 2020 growing seasons, to determine the sensitivity of azuki, kidney, small red, and white beans to tiafenacil applied preemergence (PRE) at 12.5, 25, 50, and 100 g ai ha−1. Tiafenacil applied at 100 g ai ha−1 caused 5% or less injury to azuki, kidney, small red, and white beans: 0% to 3% injury to azuki bean; 1% to 5% injury to kidney bean; and 1% to 4% injury to both small red bean and white bean. Tiafenacil applied PRE at 12.5, 25, 50, and 100 g ai ha−1 caused up to 1%, 4%, 4%, and 5% visible dry bean injury, respectively, but had no negative effect on other measured growth parameters including seed yield. Crop injury was generally greatest when tiafenacil was appled at the 100 g ai ha−1 rate in dry beans. Generally, kidney, small red, and white bean were more sensitive to tiafenacil than azuki bean. Dry bean injury was persistent and increased with time with the greatest injury observed 8 wk after emergence. Tiafenacil applied PRE can be a useful addition to the current strategies to control grass and broadleaf weeds, especially glyphosate-resistant horseweed and amaranth species prior to bean emergence.

Bodies of water that are treated with herbicides for aquatic weed control are often used as a source of irrigation water by landowners near the water body, but there is little information regarding the effects of experimental aquatic herbicides on common garden plants. Therefore, the goal of these experiments was to identify phytotoxicity of four herbicides on vegetables frequently cultivated by home gardeners. Sweet pepper, zucchini, tomato, and bush bean were irrigated with water containing bispyribac-sodium, quinclorac, topramezone, and trifloxysulfuron-sodium to identify the herbicide concentrations that damage these garden vegetables. Experiments were conducted during 2009 and repeated in 2010. Plants were irrigated four times during an 11-d period with the equivalent of 1.27 cm of treated water during each irrigation, then irrigated with well water until they were harvested 41 d after the first herbicide treatment. Values of the concentration of herbicide expected to reduce treated plants by 10% compared with control plants (EC10) were calculated from components of nonlinear regression. Analysis of visual quality and dry weight data revealed that bush bean was the most sensitive of the vegetable plants to bispyribac-sodium, trifloxysulfuron-sodium, and topramezone, whereas the species most sensitive to quinclorac was zucchini. Exposure of bush bean to 7.1, 0.9, and 1.2 parts per billion (ppb) of bispyribac-sodium, trifloxysulfuron-sodium, and topramezone, respectively, would be expected to cause 10% reductions compared with control plants, whereas exposure of zucchini to as little as 11.0 ppb of quinclorac would be expected to cause a 10% reduction in dry weight.

Smellmelon is an invasive weed in the Golestan and Mazandran provinces of Iran. In a series of experiments, germination of freshly harvested seeds, cardinal temperatures, plant burial depth, and distribution and chemical control of smellmelon were evaluated to assist us in developing a management program to help growers manage this weed more effectively. The optimal seed germination temperature was estimated at 32.7 C by a two-piece segmented model. Mature fresh seeds of smellmelon exhibited no dormancy, whereas mucilage of the seed negatively affected germination. The greatest seed sowing depth from which seedlings emerged was 5 cm. Geographical distribution of smellmelon occurred up to an elevation of 350 m above sea level, whereas the density of smellmelon decreased at elevations higher than 151 m. Imazethapyr reduced plant growth and the reproductive capacity of smellmelon. Germination of seed from smellmelon plants treated with imazethapyr was significantly reduced compared with seed treated with bentazon or bentazon plus acifluorfen. A combination of tillage of deeper than 5 cm, early planting time, and the use of imazethapyr can reduce smellmelon competition in various field crops.

Rapeseed is a popular cover crop choice due to its deep-growing taproot, which creates soil macropores and increases water infiltration. Brassicaceae spp. that are mature or at later growth stages can be troublesome to control. Experiments were conducted in Delaware and Virginia to evaluate herbicides for terminating rapeseed cover crops. Two separate experiments, adjacent to each other, were established to evaluate rapeseed termination by 14 herbicide treatments at two timings. Termination timings included an early and late termination to simulate rapeseed termination prior to planting corn and soybean, respectively, for the region. At three locations where rapeseed height averaged 12 cm at early termination and 52 cm at late termination, glyphosate + 2,4-D was most effective, controlling rapeseed 96% 28 d after early termination (DAET). Paraquat + atrazine + mesotrione (92%), glyphosate + saflufenacil (91%), glyphosate + dicamba (91%), and glyphosate (86%) all provided at least 80% control 28 DAET. Rapeseed biomass followed a similar trend. Paraquat + 2,4-D (85%), glyphosate + 2,4-D (82%), and paraquat + atrazine + mesotrione (81%) were the only treatments that provided at least 80% control 28 d after late termination (DALT). Herbicide efficacy was less at Painter in 2017, where rapeseed height was 41 cm at early termination, and 107 cm at late termination. No herbicide treatments controlled rapeseed >80% 28 DAET or 28 DALT at this location. Herbicide termination of rapeseed is best when the plant is small; termination of large rapeseed plants may require mechanical of other methods beyond herbicides.

In recent years, there has been increased use of dicamba due to the introduction of dicamba-resistant cotton and soybean in the United States. Therefore, there is a potential increase in off-target movement of dicamba and injury to sensitive crops. Flue-cured tobacco is extremely sensitive to auxin herbicides, particularly dicamba. In addition to yield loss, residue from drift or equipment contamination can have severe repercussions for the marketability of the crop. Studies were conducted in 2016, 2017, and 2018 in North Carolina to evaluate spray-tank cleanout efficiency of dicamba using various cleaning procedures. No difference in dicamba recovery was observed regardless of dicamba formulation and cleaning agent. Dicamba residue decreased with the number of rinses. There was no difference in dicamba residue recovered from the third rinse compared with residue from the tank after being refilled for subsequent tank use. Recovery ranged from 2% to 19% of the original concentration rate among the three rinses. Field studies were also conducted in 2018 to evaluate flue-cured tobacco response to reduced rates of dicamba ranging, from 1/5 to 1/10,000 of a labeled rate. Injury and yield reductions varied by environment and application timing. When exposed to 1/500 of a labeled rate at 7 and 11 wk after transplanting, tobacco injury ranged from 39% to 53% and 10% to 16% 24 days after application, respectively. The maximum yield reduction was 62%, with a 55% reduction in value when exposed to 112 g ha−1 of dicamba. Correlations showed significant relationships between crop injury assessment and yield and value reductions, with Pearson values ranging from 0.24 to 0.63. These data can provide guidance to growers and stakeholders and emphasize the need for diligent stewardship when using dicamba technology.

Biotypes of Palmer amaranth that are resistant to acetolactate synthase (ALS) inhibitor are becoming widespread in western Nebraska. There are limited effective postemergence (POST) herbicides labeled for ALS-inhibitor-resistant Palmer amaranth control in dry edible bean. The objective of this study was to evaluate the efficacy of dimethenamid-P in a sequential preemergence (PRE) fb followed by (fb) POST program at two POST application timings, the first and third trifoliate stages (V1 and V3, respectively), for controlling ALS-inhibitor-resistant Palmer amaranth in dry edible bean. A field study was conducted in 2019, 2020, and 2021 in Scottsbluff, NE. PRE-alone applications of pendimethalin + dimethenamid-P provided inconsistent Palmer amaranth control. Dimethenamid-P applied POST following a PRE application of pendimethalin + dimethenamid-P provided effective (>90%) Palmer amaranth control at 4 wk after V3 only at the V1 application timing in 2019. In 2020 and 2021 dimethenamid-P applied POST at V1 and V3 following a PRE application of pendimethalin + dimethenamid-P provided 99% and 98% Palmer amaranth control at 4 wk after V3, and 98% and 94% Palmer amaranth control at harvest, respectively. Palmer amaranth biomass was reduced by 95% to 99% and by 96% to 98% compared with the -nontreated control when dimethenamid-P was applied POST at V1 and V3, respectively, following a PRE application of pendimethalin + dimethenamid-P in 2020 and 2021. Application of a mixture of dimethenamid-P with imazamox + bentazon POST provided similar results to those of the fomesafen-containing treatments and dimethenamid-P alone POST. Dimethenamid-P applied POST following a PRE application of pendimethalin + dimethenamid-P resulted in similar yield as the fomesafen-containing treatments. If fomesafen is not an option due to the crop rotation interval restriction, using dimethenamid-P in a sequential PRE fb POST program is the only effective alternative to control ALS-inhibitor–resistant Palmer amaranth in Nebraska. The use of dimethenamid-P in a sequential PRE fb POST program, alone or mixed with foliar-active herbicides should be considered by dry edible bean growers who are dealing with ALS-inhibitor-resistant Palmer amaranth.

Glyphosate is an important component of herbicide programs in orchard crops in California. It can be applied alone or in tank-mix combinations under the crop rows or to the entire field and often is used multiple times each year. There has been speculation about the potential impacts of repeated use of glyphosate in perennial crop systems, because of uptake from shallow root systems or indirectly because of effects on nutrient availability in soil. To address these concerns, research was conducted from 2013 to 2020 on key orchard crops to evaluate tree response to glyphosate regimens. Almond, cherry, and prune were evaluated in separate experiments. In each crop, the experimental design was a factorial arrangement of two soil types, four glyphosate rates (0, 1.1, 2.2, and 4.4 kg ae ha−1, applied three times annually), and two post-glyphosate application irrigation treatments. In the first 2 yr of the study, there was no clear impact of the glyphosate regimens on shikimate accumulation or leaf chlorophyll content, which suggested no direct effect on the crop. In the seventh year of the study, after six consecutive years of glyphosate application to the orchard floors, there were no negative impacts of glyphosate application on leaf nutrient concentration or on cumulative trunk growth in any of the three orchard crops. Lack of a negative growth impact even at the highest treatment rate, which included 18 applications of glyphosate totaling nearly 80 kg ae ha−1 glyphosate over the course of the experiment suggest there is not likely a significant risk to tree health of judicious use of the herbicide in these production systems. Given the economic importance of orchard crops in California, and grower and industry concerns about pesticides generally and specifically about glyphosate, these findings are timely contributions to weed management concerns in perennial specialty crops.

Virginia buttonweed is a difficult-to-control weed in southern turfgrass. Typically, auxin-type herbicides are considered to be the standard treatment for this species. Field experiments were conducted to compare the efficacy of flazasulfuron, a sulfonylurea herbicide, to pyridine herbicides on Virginia buttonweed. Treatments included single and sequential applications of flazasulfuron (0.05 or 0.08 kg ai/ha). The sequential applications were applied 3 and 6 wk after initial treatment (WAIT). Three applications of 0.05 and 0.08 kg/ha flazasulfuron controlled Virginia buttonweed greater than 93% at 10 WAIT. Both treatments were comparable to 0.6 kg ai/ha triclopyr + 0.2 kg ai/ha clopyralid (80% control). These studies indicated that increased application of flazasulfuron increased Virginia buttonweed control regardless of application rates evaluated.

Field experiments were conducted in southern Wisconsin from 1996 to 1998 to evaluate the effects of acetochlor applied preemergence (PRE) followed by nicosulfuron or sethoxydim applied postemergence (POST) and of cultivation on woolly cupgrass control, corn grain yield, and woolly cupgrass seed production. Sethoxydim treatments provided greater woolly cupgrass control than nicosulfuron treatments in 1997 and similar control to nicosulfuron treatments in 1996 and 1998. However, neither herbicide killed all emerged woolly cupgrass plants, regardless of herbicide rate or POST application timing. Late postemergence treatments provided greater season-long control than early postemergence treatments in 1996 and 1998, but there was no difference in control between timings in 1997. Acetochlor applied PRE at 1,800 g ai/ha (1×) followed by nicosulfuron (35 g ai/ha) or sethoxydim (213 g ai/ha) at the registered rate (1×) or at one half of the registered rate (0.5×) consistently provided sufficient woolly cupgrass control to maximize corn yield, regardless of cultivation or POST herbicide application timing. Acetochlor PRE treatments, cultivated and noncultivated, followed by sethoxydim POST and cultivated acetochlor PRE treatments followed by nicosulfuron POST treatments provided sufficient control in each year to limit woolly cupgrass seed production to a level that decreased the predicted future seedbank density, regardless of herbicide rate or POST herbicide application timing. However, noncultivated acetochlor treatments followed by nicosulfuron applied at 1× followed by 0.5× or at 0.5× followed by 0.5× did not consistently reduce seed production to a level that decreased the predicted future seedbank density. These results suggest that the rate of sethoxydim can be reduced to 0.5× if a full rate of acetochlor is applied PRE with little effect on corn yield or woolly cupgrass seedbank density. However, reducing the rate of nicosulfuron to 0.5× following an application of acetochlor at the full rate or reducing both the acetochlor and nicosulfuron or sethoxydim rate to 0.5× is recommended only if a cultivation is planned.

Cogongrass continues to be one of the most invasive weeds in the subhumid savanna. Herbicide application expenses depend on equipment costs, costs of water transport for spraying, and chemical costs. In three on-farm experiments on land heavily infested with cogongrass, the effectiveness of a knapsack sprayer (KS), a very low volume sprayer (VLV), and a rope wick (RW) applicator was tested at Ijaye, Nigeria, from 2000 to 2001. The sprayers differed in application method, price, and carrier volume required. The dose–response curves for the three applicators were identical in all parameters except at very high doses for the RW. Consequently, there were no apparent differences in glyphosate effectiveness, even when it was applied with different equipment and different carrier volumes. However, even at very high doses, the RW was not as efficient as was the KS and VLV. Actual biomass reduction of cogongrass was greater with the KS and VLV. Even though the KS and VLV generally gave better control levels than the RW, the latter is more user-friendly because it does not require protective masks, which are often unavailable in sub-Saharan Africa. In a situation with labor scarcity, weeding with the RW was cheaper than hand weeding with hoes. The VLV was more economical when used on areas larger than 10 ha than was the RW. The KS was more economical than all other methods when used on areas larger than 2 ha.

The effects of metribuzin herbicide and phorate insecticide were studied on summer harvest chipping-potatoes at Muscatine, IA, from 1989 to 1991. Phorate at 1.5 kg/ha increased total and ‘A’-size tuber yield and tuber specific gravity. Metribuzin applied at 0.56 kg/ha postemergence decreased total and ‘A’-size tuber yield. Metribuzin applied at 0.56 kg/ha preemergence and 0.28 kg/ha postemergence did not reduce Atlantic cultivar yield. Metribuzin did not affect ‘B’-size tuber yield or specific gravity. Phorate in combination with metribuzin did not increase plant injury or reduce tuber yield.

Alachlor at 3.4 and 6.7 kg ha-1, metolachlor at 2.8 and 5.6 kg ha-1, and propachlor at 4.5 and 9.0 kg ha-1 were applied to grain sorghum in field experiments conducted in 1981 and 1982. ‘Dekalb E-59’ and ‘Pioneer 8311’ grain sorghum were tested with and without the seed protectants cyometrinil and flurazole in both experiments. ‘Funk's G-1350’ was tested with and without cyometrinil and CGA-92194 in one experiment. Alachlor and metolachlor caused serious injury (stunting and, in some instances, reductions in stand and yield) to grain sorghum without the seed protectants. Less severe injury to grain sorghum occurred with alachlor and metolachlor at high rates even in the presence of the seed protectants. The three seed protectants were equally effective in preventing crop injury. Only minor injury to grain sorghum, with or without the seed protectants, occurred with propachlor at both rates. Overall, early-season weed control was 81 to 100%; however, propachlor at the rates tested was noticeably weaker than alachlor and metolachlor against some annual grasses.

Field studies were conducted near Oxnard, CA and in two locations near Salinas, CA in 2002 and 2003 to evaluate efficacy and safety of six herbicides in celery. s-metolachlor at 0.6 and 0.7 kg ai/ha and flufenacet at 0.5, 0.6, and 0.7 kg ai/ha PRE were safe to celery and controlled 81 to 94% of yellow nutsedge at densities < 20 plants/m2. At yellow nutsedge densities > 20 plants/m2, the most efficacious treatments were 1.1 kg/ha of s-metolachlor or 0.7 kg/ha of flufenacet, which reduced nutsedge densities by 71 or 53%, respectively; however, both resulted in slight injury to celery. All other herbicides generally did not injure celery and none reduced marketable crop yield. Flumioxazin pretransplant (PRE) at 0.1 and 0.2 kg ai/ha controlled broadleaf weeds near 100% at all locations, suggesting that it can be an effective alternative to standard linuron and prometryn, which are applied post-transplant (POST) in celery.

Greenhouse and growth chamber experiments were conducted to investigate the sprouting potential of rootstock; the effect of temperature, burial depth, and length of rootstock on sprouting; and the effect of shoot removal on resprouting ability of rootstock in redvine and trumpetcreeper. Glyphosate translocation along the rootstock of redvine was also measured. Higher sprouting was observed at 20 to 40 C in trumpetcreeper (60 to 73%) and at 30 to 40 C in redvine (45 to 47%) compared with other temperatures. Redvine sprouting was totally inhibited at 15 C, whereas trumpetcreeper had a sprouting of 12%. Emergence of shoot from a 28-cm planting depth was completely inhibited in redvine, whereas trumpetcreeper had 23% sprout emergence. After shoot removal treatments applied every 3 wk, redvine rootstock segments ≤2 cm long were totally depleted after fifth shoot removal treatment (15 wk after planting [WAP]). In trumpetcreeper, total depletion was not reached by 15 WAP, regardless of rootstock length. 14C-glyphosate was translocated from the treated shoot attached to the apical end of a 35-cm rootstock to the untreated end with slightly less 14C-glyphosate recovered at the untreated end compared with 5 to 10 cm from the treated shoot. These results indicated that vegetative reproduction in redvine is more sensitive to cool temperatures, deep burial depth, and short rootstock segment than trumpetcreeper. Variable control of redvine with glyphosate could be due to inadequate herbicide translocation within the rootstock.

Full canopy closure and light interception are critical to obtaining full yield potential of ultra-short–season soybean in the midsouthern United States. We hypothesized that herbicide applications that resulted in soybean leaf injury would reduce season-long light interception and yield of ultra-short–season soybean grown in this environment. Experiments were conducted in 2001, 2002, and 2003 at Fayetteville, AR, to determine the effect of the diphenylether herbicides acifluorfen and lactofen on light interception and yield of maturity group (MG) 0 and II soybean. Factors evaluated included soybean MG, herbicide rate, treatment timing, and soybean seeding density. When applied at soybean growth stage (GS) V3, 0.2 kg ai/ha lactofen reduced green leaf area immediately after application and final canopy closure relative to soybean treated with 0.6 or 0.2 kg/ha acifluorfen and untreated soybean. Herbicide application did not affect yield of well-watered soybean when applied at GS V3 in 2001 or at early reproductive development in 2003. In 2002, an irrigation problem resulted in a period of water-deficit stress during seed fill of MG II soybean. Under these conditions, treatment with acifluorfen at GS V3 reduced soybean yield, and treatment with lactofen during early reproductive development reduced soybean yield, relative to untreated soybean. This research indicates that diphenylether herbicides can be safely applied to well-watered ultra-short–season soybean, but yield reduction can occur when applied to soybean that is not well watered.

Management of volunteer glyphosate-resistant (GR) corn may be problematic in soybean resistant to glyphosate and 2,4-D or dicamba, as auxinic herbicides often antagonize graminicide efficacy. Field and greenhouse trials were conducted using mixtures of 2,4-D or dicamba in combination with glyphosate and clethodim-A (formulated without an adjuvant) or clethodim-SM (adjuvant-inclusive formulation) to determine the effect on volunteer GR corn control. Neither auxinic herbicide reduced clethodim efficacy, regardless of clethodim rate or formulation in field trials. However, the addition of glyphosate to these mixtures at the 35 g ai ha−1 clethodim dose reduced control from clethodim-A and clethodim-SM by 62% to 75% and 27% to 47%, respectively. Increasing the clethodim dose to 105 g ha−1 or greater in combination with glyphosate and either auxinic herbicide generally restored clethodim efficacy (74% to 98% control); in one site-year, the addition of glyphosate plus dicamba to clethodim-A at 140 g ha−1 still reduced control by 34%. In greenhouse experiments, clethodim-A efficacy was reduced by 17% and 28% when applied with glyphosate plus 420 and 1,680 g ae ha−1 2,4-D, respectively, in the absence of crop oil concentrate (COC). Increasing the dose of dicamba in a similar mixture had a negligible effect. Irrespective of auxinic herbicide dose, the inclusion of COC to clethodim-A mixtures with glyphosate plus 2,4-D or dicamba resulted in ≥ 90% control. These results specify an enhanced risk of reduced clethodim efficacy on volunteer GR corn when glyphosate is added to mixtures containing 2,4-D or dicamba. To optimize control from these mixtures, clethodim should be applied at ≥ 105 g ha−1 and should include an activator adjuvant in the form of COC and/or an adjuvant-inclusive clethodim formulation. This recommendation contrasts with several labels of clethodim that do not require COC when applied with adjuvant-loaded glyphosate products.

Giant ragweed is one of the most competitive annual broadleaf weeds in corn and soybean crop production systems in the United States and eastern Canada. Management of giant ragweed has become difficult due to the evolution of resistance to glyphosate and/or acetolactate synthase (ALS)-inhibitor herbicides and giant ragweed’s ability to emerge late in the season, specifically in the eastern Corn Belt. Late-season herbicide application may reduce seed production of weed species; however, information is not available about late-season herbicide applications on giant ragweed seed production. The objective of this study was to evaluate the effect of single or sequential late-season applications of 2,4-D, dicamba, glyphosate, and glufosinate on inflorescence injury and seed production of glyphosate-resistant (GR) giant ragweed under greenhouse and field conditions (bare ground study). Single and sequential applications of glufosinate resulted in as much as 59 and 60% injury to giant ragweed inflorescence and as much as 78 and 75% reduction in seed production, respectively, under field and greenhouse conditions. In contrast, single or sequential applications of 2,4-D or dicamba resulted in ≥ 96% inflorescence injury and reduction in seed production in the field as well as in greenhouse studies. The results indicated that 2,4-D or dicamba are effective options for reducing seed production of glyphosate-resistant giant ragweed even if applied late in the season. Targeting weed seed production to decrease the soil seedbank will potentially be an effective strategy for an integrated management of GR giant ragweed.

Tolpyralate is a new 4-hydroxyphenyl-pyruvate dioxygenase (HPPD)–inhibiting herbicide for weed control in corn. Previous research has reported efficacy of tolpyralate + atrazine on several annual grass and broadleaf weed species; however, no studies have evaluated weed control of tolpyralate + atrazine depending on time-of-day (TOD) of application. Six field experiments were conducted over a 2-yr period (2018, 2019) near Ridgetown, ON, to determine if there is an effect of TOD of application on tolpyralate + atrazine efficacy on common annual grass and broadleaf weeds. An application was made at 3-h intervals beginning at 06:00 h with the last application at 24:00 h. There was a slight TOD effect on velvetleaf, pigweed species, and common ragweed control with tolpyralate + atrazine; however, the magnitude of change throughout the day was ≤3% at 2, 4, or 8 wk after application (WAA). There was no effect of TOD of tolpyralate + atrazine on the control of lambsquarters, barnyardgrass, and green foxtail. All weed species were controlled ≥88% at 8 WAA. There was no effect of TOD of tolpyralate + atrazine application on corn yield. Results of this study show no evidence of a TOD effect on weed control efficacy with tolpyralate + atrazine.

Experiments were conducted in the greenhouse to determine the effects of adjuvant and herbicide concentrations on imazamox, imazethapyr, nicosulfuron, and ICIA 0604 phytotoxicity, independent of spray retention. Equal amounts of herbicide were applied to oat in a single 0.5-μl drop or four 0.5-μl drops. Changes in adjuvant concentration influenced herbicide phytotoxicity more with application in one concentrated drop rather than in four dilute drops. Overall, herbicide phytotoxicity was greater when low adjuvant concentrations were applied in four dilute drops compared with a single concentrated drop. But when the same total amount of adjuvant was applied in one or four drops, herbicide phytotoxicity in a single drop was generally equal to or greater than in four drops. These results suggest that high herbicide phytotoxicity with high herbicide and adjuvant concentrations in low spray volumes in the field was primarily because of increased herbicide absorption rather than spray retention.