Herbicide drift to sensitive crops can result in significant injury, yield loss, and even crop destruction. When pesticide drift is reported to the Georgia Department of Agriculture (GDA), tissue samples are collected and analyzed for residues. Seven field studies were conducted in 2020 and 2021 in cooperation with the GDA to evaluate the effect of (1) time interval between simulated drift event and sampling, (2) low-dose herbicide rates, and (3) the sample collection methods on detecting herbicide residues in cotton (Gossypium hirsutum L.) foliage. Simulated drift rates of 2,4-D, dicamba, and imazapyr were applied to non-tolerant cotton in the 8- to 9-leaf stage with plant samples collected at 7 or 21 d after treatment (DAT). During collection, plant sampling consisted of removing entire plants or removing new growth occurring after the 7-leaf stage. Visual cotton injury from 2,4-D reached 43% to 75% at 0.001 and 0.004 kg ae ha−1, respectively; for dicamba, it was 9% to 41% at 0.003 or 0.014 kg ae ha−1, respectively; and for imazapyr, it was 1% to 74% with 0.004 and 0.03 kg ae ha−1 rates, respectively. Yield loss was observed with both rates of 2,4-D (11% to 51%) and with the high rate of imazapyr (52%); dicamba did not influence yield. Herbicide residues were detected in 88%, 88%, and 69% of samples collected from plants treated with 2,4-D, dicamba, and imazapyr, respectively, at 7 DAT compared with 25%, 16%, and 22% when samples were collected at 21 DAT, highlighting the importance of sampling quickly after a drift event. Although the interval between drift event and sampling, drift rate, and sampling method can all influence residue detection for 2,4-D, dicamba, and imazapyr, the factor with the greatest influence is the amount of time between drift and sample collection.

Cole crops including broccoli and collard contribute more than $119 million to Georgia’s farm gate value yearly. To ensure maximum profitability, these crops must be planted into weed-free fields. Glyphosate is a tool often used to help achieve this goal because of its broad-spectrum activity on weeds coupled with the knowledge that it poses no threat to the succeeding crop when used as directed. However, recent research suggests that with certain soil textures and production systems, the residual soil activity of glyphosate may damage some crops. Therefore, field experiments were conducted in fall 2019 and 2020 to evaluate transplanted broccoli and collard response to glyphosate applied preplant onto bare soil and what practical mitigation measures could be implemented to reduce crop injury. Herbicide treatments consisted oGf 0, 2.5, or 5 kg ae ha−1 glyphosate applied preplant followed by 1) no mitigation measure, 2) tillage, 3) irrigation, or 4) tillage and irrigation prior to transplanting broccoli and collard by hand. When no mitigation was implemented, the residual activity of glyphosate at 2.5 and 5.0 kg ae ha−1 resulted in 43% to 71% and 79% to 93% injury to broccoli and collard transplants, respectively. This resulted in a 35% to 50% reduction in broccoli marketable head weights and 63% to 71% reduction in collard leaf weights. Irrigation reduced visible damage by 28% to 48%, whereas tillage reduced injury by 43% to 76%, for both crops. Irrigation alleviated yield losses for broccoli but only tillage eliminated yield loss for both crops. Care must be taken when transplanting broccoli and collard into a field recently treated with glyphosate at rates ≥2.5 kg ae ha−1. Its residual activity can damage transplants with injury levels influenced by glyphosate rate, and tillage or irrigation after application and prior to planting.

The tolerance of cereal rye to eight herbicides registered for use in wheat, at two rates, was evaluated for potential labeling in cereal rye to expand limited chemical weed control options. Across five site-years, halauxifen-methyl + florasulam, pyroxsulam, and thifensulfuron-methyl + tribenuron-methyl applied at a 2X rate to cereal rye at Zadoks (Z) 13 caused less than 15% injury and had no impact on cereal rye density. These herbicides at the 2X rate reduced cereal rye heights 11% at 10 days after treatment (DAT), with rye recovering by 31 DAT; cereal rye heights were not reduced with these herbicides at their 1X rate. In contrast, significant injury was observed with the 1X rate of mesosulfuron-methyl (45%), pinoxaden (27%), and pinoxaden + fenoxaprop-P-ethyl (30%) applied postemergence; early-season height was reduced 19% to 26%. Residual herbicide pyroxasulfone applied as a delayed preemergence at Z 10 and flumioxazin + pyroxasulfone applied at Z 11 caused 27% to 28% and 16% to 47% injury, respectively, when the 1X rate was activated by rainfall within 2 d of application. These residual herbicides reduced cereal rye height and density up to 35% and 40%, respectively. Cereal rye grain yield was not influenced by herbicide or rate applied.

Georgia vegetable growers produce more than 27% of the nation’s fresh-market cucumbers. To maximize yields and profit, fields must be weed-free when planting. Limitations with current burndown herbicide options motivated academic, industry, and U.S. Department of Agriculture partners to search for new tools to assist growers. One possibility, glufosinate, controls many common and troublesome weeds, but its influence on cucumber development through residual activity when applied before or at planting is not understood. Thus, four different studies were each conducted two to four times from 2017 to 2020 to determine 1) transplant cucumber response to preplant glufosinate applications as influenced by rate, overhead irrigation, and interval between application and planting; and 2) seeded cucumber response to preemergence (PRE) glufosinate applications as influenced by rate, overhead irrigation, and planting depth. Glufosinate applied at 330, 660, 980, and 1,640 g ai ha−1 the day before transplanting caused 11% to 53% injury on sandy, low organic matter soils. Cucumber vine lengths and plant biomass were reduced up to 28% and 46%, respectively, with the three highest rates. Early-season yield (harvests 1 to 4) noted a 31% to 60% yield loss with glufosinate at 660 to 1,640 g ha−1 with similar trends observed with total yield (11 to 13 harvests). Irrigation (0.75 cm) after application and before transplanting reduced injury to less than 21%, eliminated vine length and biomass suppression except at the highest rate, and eliminated yield loss. Extending the interval between glufosinate application and transplanting from 1 to 4 d was not beneficial, and further extending the interval to 7 d significantly reduced injury half the time. When applied PRE to seeded cucumber and combining the data across locations, glufosinate caused less than 7% injury even at 1,640 g ha−1. Seeded plant vine lengths, biomass, and marketable yield were not influenced by the PRE application, and neither irrigation nor planting depth influenced seeded crop response to glufosinate.

Glyphosate and paraquat are effective preplant burndown herbicide options for multicrop vegetable production that uses plastic mulch, but problematic weeds such as wild radish, cutleaf evening primrose, annual morningglory, or horseweed may not be adequately controlled with these herbicides alone. The herbicides 2,4-D and dicamba could help control these troublesome weeds prior to planting if they can be removed from plastic mulch and thus avoid crop damage. Treatments included 2,4-D (1,065 and 2,130 g ae ha−1) and dicamba (560 and 1,120 g ae ha−1) applied broadcast over plastic mulch a day before transplanting. Just before transplanting, treatments received either 0.76 cm of water via overhead irrigation or no irrigation. Plastic mulch samples were collected at application and planting to determine herbicide presence using analytical techniques, and cantaloupe and zucchini squash were subsequently transplanted on the plastic beds. Analytical ultra-high performance liquid chromatography revealed that 88% to 99% of the initial herbicide concentration was present at crop planting when irrigation was not implemented. At most, a 1/50 rate of dicamba and a 1/500 rate of 2,4-D was present at planting when overhead irrigation was applied prior to transplanting. Maximum cantaloupe and squash injury from 2,4-D with irrigation was 10% and did not influence plant growth, biomass, or yield. For dicamba with overhead irrigation, cantaloupe injury was 35%, vine lengths were reduced by 24%, and maturity was delayed, whereas squash injury ranged from 9% to 12%, with no influence on growth or yield. Without irrigation to wash herbicides from the mulch prior to planting, 60% to 100% injury of both crops occurred with both herbicides. Zucchini squash was more tolerant to dicamba than cantaloupe. Results demonstrated that 2,4-D can be adequately removed from the surface of plastic mulch with irrigation, whereas a single irrigation event was not sufficient to remove dicamba.

The loss of methyl bromide led vegetable growers to rely more heavily on herbicides to control weeds. Although herbicides can be effective, limited options in vegetable production challenge growers. Identifying new, effective tools to be applied over plastic mulch before planting, for improved weed control with minimal crop injury, would be beneficial. The objective of these experiments was to evaluate the persistence of preplant applications of glyphosate (1,125 or 2,250 g ae ha−1) plus 2,4-D (1,065 or 2,130 g ae ha−1) or dicamba (560 g ae ha−1) over plastic mulch, using analytical techniques and subsequent yellow squash and watermelon response. Glyphosate and 2,4-D were not analytically detected at damaging concentrations on plastic mulch when at least 3.5 cm of rainfall was received after application and before planting. In addition, bioassay results showing less than 10% visual injury for either squash and watermelon, with no growth or yield suppression observed, supported analytical results. In contrast, dicamba concentrations on plastic mulch, regardless of rainfall amount or time between application and planting, remained at damaging levels. Squash yields were reduced by dicamba applied 1 to 30 d before planting, whereas watermelon was more resilient. 2,4-D plus glyphosate applied preplant over plastic mulch can provide an additional herbicide option for vegetable growers. More research is needed to understand the impact of residual activity of 2,4-D when transplants land directly in holes in plastic mulch at the time of application. The relationship of dicamba with plastic mulch is complex, because the herbicide cannot be easily removed by rainfall. Thus, dicamba should not be included in a weed management system in plasticulture vegetable production.

Agronomic crops engineered with resistance to 2,4-D or dicamba have been commercialized and widely adopted throughout the United States. Because of this, increased use of these herbicides in time and space has increased damage to sensitive crops. From 2014 to 2016, cucumber and cantaloupe studies were conducted in Tifton, GA, to demonstrate how auxinic herbicides (namely, 2,4-D or dicamba), herbicide rate (1/75 or 1/250 field use), and application timing (26, 16, and 7 d before harvest [DBH] of cucumber; 54, 31, and 18 DBH of cantaloupe) influenced crop injury, growth, yield, and herbicide residue accumulation in marketable fruit. Greater visual injury, reductions in vine growth, and yield loss were observed at higher rates when herbicides were applied during early-season vegetative growth compared with late-season with fruit development. Dicamba was more injurious in cucumber, whereas cantaloupe responded similarly to both herbicides. For cucumber, total fruit number and relative weights were reduced (16% to 19%) when either herbicide was applied at the 1/75 rate 26 DBH. Cantaloupe fruit weight was also reduced 21% and 10% when either herbicide was applied at the 1/75 rate 54 or 31 DBH, respectively. Residue analysis noted applications made closer to harvest were more likely to be detectable in fruit than earlier applications. In cucumber, dicamba was detected at both rates when applied 7 DBH, whereas in cantaloupe, it was detected at both rates when applied 18 or 31 DBH in 2016 and at the 1/75 rate applied 18 or 31 DBH in 2014. Detectable amounts of 2,4-D were not observed in cucumber but were detected in cantaloupe when applied at either rate 18 or 31 DBH. Although early-season injury will more likely reduce cucumber or cantaloupe yields, the quantity of herbicide residue detected will be most influenced by the time interval between the off-target incident and sampling.

Dicamba and 2,4-D systems control many problematic weeds; however, drift to susceptible crops can be a concern in diverse production areas. Glufosinate-based systems are an alternative, but current recommended rates of glufosinate can result in variable control. Research was conducted in 2017 and 2018 to investigate the optimum time interval between sequential glufosinate applications and determine if the addition of glyphosate with glufosinate is beneficial for controlling Palmer amaranth and annual grasses in cotton. The interval between sequential applications (1, 3, 5, 7, 10, or 14 d or no second spray) was the whole plot and herbicide option (glufosinate or glufosinate plus glyphosate) was the subplot. Combined over herbicides, Palmer amaranth 15- to 20-cm tall (at four locations) was controlled 98% to 99% with sequential intervals of 1 to 7 d compared with 70% to 88% with intervals of 10 or 14 d. Lowest biomass weight and population densities were noted with 1- to 7-d intervals. Large crabgrass 15- to 20-cm tall (at five locations) was controlled 93% to 98% with glufosinate applications 3- to 7-d apart as compared with 76% to 81% with applications 10- to 14-d apart. Lowest biomass weights were observed with 1- to 7-d intervals. When glufosinate controlled grass less than 93%, adding glyphosate was beneficial. Neither interval between sequential applications nor herbicide option influenced cotton yield. Shorter time intervals between sequential application and including glyphosate can improve the effectiveness of a glufosinate-based system in managing Palmer amaranth and large crabgrass.

Nutsedge species are problematic in plastic-mulched vegetable production because of the weed’s rapid reproduction and ability to penetrate the mulch. Vegetable growers rely heavily on halosulfuron to manage nutsedge species; however, the herbicide cannot be applied over mulch before vegetable transplanting due to potential crop injury. This can be problematic when multiple crops are produced on a single mulch installation. Field experiments were conducted to determine the response of broccoli, cabbage, squash, and watermelon to halosulfuron applied on top of mulch prior to transplanting. Halosulfuron at 80 g ai ha−1 was applied 21, 14, 7, and 1 d before planting (DBP), and 160 g ai ha−1 was applied 21 DBP. In all experiments, extending the interval between halosulfuron application and planting reduced crop injury. For squash and watermelon, visual injury, plant diameters/vine runner lengths, marketable fruit weights, and postharvest plant biomass resulted in similar values when applying 80 g ha−1 21 DBP and with the nontreated weed-free control. Reducing this interval increased injury for both crops. Visual crop injury and yield reductions up to 40% occurred, with halosulfuron applied 14, 7, or 1 DBP in squash and 1 DBP in watermelon. Broccoli and cabbage showed greater sensitivity, with injury and plant diameter reductions greater than 15%, even with halosulfuron applied at 80 g ha−1 21 DBP. Experimental results confirm that halosulfuron binds to plastic mulch, remains active, and is slowly released from the mulch over a substantial period, during rainfall or overhead irrigation events. Extending the plant-back interval to at least 21 d before transplanting did overcome squash and watermelon injury concerns with halosulfuron at 80 g ha−1, but not broccoli and cabbage. Applying halosulfuron over mulch to control emerged nutsedge before planting squash and watermelon would be beneficial if adequate rainfall or irrigation and appropriate intervals between application and planting are implemented.