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.

Field trials were conducted near Lubbock, TX, in 2013, 2014, and 2015 to evaluate non–2,4-D–resistant cotton response to low rates of glyphosate plus 2,4-D choline. Cotton was treated with five rates of glyphosate plus 2,4-D choline (0.0183, 0.183, 1.83, 18.3, and 183 g ae ha−1) at two application timings (nine leaf and first bloom). These rates correspond to contamination rates of 0.0008%, 0.008%, 0.08%, 0.8%, and 8%, respectively. Visual cotton injury, boll retention, lint yield, and fiber properties were recorded. When averaged over contamination rates, visual injury after applications made to nine-leaf cotton was greater than for first-bloom cotton in three of 3 yr and yield loss was greater when applications were made to nine-leaf cotton when compared with first-bloom cotton in two of 3 yr. Averaged over application timing, lint yield in 2013, 2014, and 2015 after glyphosate plus 2,4-D choline contamination rates of 0.0008% and 0.008% were not different than that of the nontreated control, whereas contamination rates of 0.08%, 0.8%, and 8% decreased yield by 3% to 20%, 45% to 58%, and 80% to 96%, respectively. Contamination rates of 0.0008%, 0.008%, 0.08%, and 0.8% rarely affected fiber quality; however, a contamination rate of 8% frequently decreased micronaire, fiber length, fiber length uniformity, and fiber strength. This decrease in fiber quality also resulted in a reduction in cotton loan value and potential financial return. Although decreases in fiber quality parameters were not observed with the 0.8% contamination rate, significant reductions in financial return occurred due to yield loss caused by injury from glyphosate plus 2,4-D choline.

With the widespread occurrence of herbicide-resistant weeds in midsouthern U.S. rice, new technologies are needed to achieve adequate weed control. A new non–genetically modified rice trait has been commercialized that is resistant to quizalofop, an acetyl coenzyme A carboxylase (ACCase)-inhibiting herbicide. The addition of quizalofop-resistant rice to production systems will increase the use of quizalofop, possibly increasing the risk for injury to other grass crops. Experiments were conducted in 2014 and 2015 to determine the sensitivity of corn, grain sorghum, and conventional rice to low rates of quizalofop (1/10× to 1/200× of 160 g ai ha–1). Conventional rice was not affected by quizalofop rate or application timing. Corn displayed the greatest response to the 1/10× quizalofop rate at the two- to three-leaf stage, with 50% to 65% injury and 35% to 37% relative yield compared to the nontreated check. Grain sorghum was injured 31% to 34% by the 1/10× quizalofop rate applied at the two- to three-leaf stage, and there was 20% to 26% injury at the panicle exertion growth stage. The highest rate of quizalofop at the panicle exertion stage reduced yields 28% to 46%. Overall, risk for injury to any of the three evaluated crops from quizalofop appears low, with greatest injury observed at the highest quizalofop drift rate, with minimal injury at lower rates.

Cotton (Gossypium hirsutum L.) response was evaluated when propanil (3′,4′-dichloropropionanilide), thiobencarb {S-[(4-chlorophenyl)methyl] diethylcarbamothioate}, butachlor [N-(butoxymethyl)-2-chloro-2′,6′-diethylacetanilide], oxadiazon [2-tert-butyl-4-(2,4-dichloro-5-isopropoxyphenyl)-δ2-1,3,4-oxadiazolin-5-one], bifenox [methyl-5-(2,4-dichlorophenoxy)-2-nitrobenzoate], acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid}, and metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] were applied over-the-top at simulated drift rates at two growth stages during 1975 to 1979. No rate of butachlor or thiobencarb injured cotton. The order of phytotoxicity for the herbicides applied to cotyledonary cotton was propanil > metribuzin > bifenox > oxadiazon > acifluorfen > butachlor = thiobencarb. Herbicides injured cotton less at the five- or eight-node stage than at the cotyledonary stage. Injury was more severe in seasons of wet or cold weather during early plant development.

Glyphosate was applied to pepper as single or sequential applications to assess the consequences of drift or other accidental exposures. Foliar injury increased and plant vigor declined with increased rates of glyphosate and were exacerbated by a second application. Single applications at flowering (stage 1) were more damaging than single applications after fruit set (stage 2). Decline in marketable yield with increased glyphosate rate was greater with stage 1 applications, except in spring 1987 when marketable yields with single applications of glyphosate at stage 1 or stage 2 were statistically similar. Sequential applications resulted in the lowest marketable yields. Total yields declined with increased glyphosate rate and decline was more pronounced with sequential applications than with single applications. Total yield was affected to a greater extent when glyphosate was applied at stage 1 than at stage 2. Yield was more sensitive to two successive exposures than to single applications. Mean fruit weight was reduced by glyphosate in two of the four experiments.