Introducing soybean cultivars resistant to 2,4-D and dicamba allowed for postemergence applications of these herbicides. These herbicides pose a high risk for off-target movement, and the potential influence on crops such as hemp is unknown. Two studies were conducted from 2020 through 2022 in controlled environments to evaluate hemp response to rates simulating off-target events of 2,4-D and dicamba. The objectives of these studies were to (1) determine the effects of herbicide (2,4-D and dicamba) and rate (1× to 1/100,000× labeled rate) on visible injury, height, and branching, and (2) determine the effect of 2,4-D rate (1× to 1/100,000× labeled rate) on visible injury, height, branching, and reproductive parameters. Herbicides were applied in the early vegetative stage, and evaluations took place 14 and 28 d after treatment (DAT) and at trial termination (42 DAT in the greenhouse trial and at harvest in the growth chamber trial). In the greenhouse study, 2,4-D and dicamba at the 1× rate, and the 1/10× rate of dicamba, caused 68%, 78%, and 20% injury 28 DAT, respectively. At the time of trial termination 42 DAT, plants treated with 1× rates of 2,4-D and dicamba, or 1/10× dicamba, were 19, 25, and 9 cm shorter than the nontreated control, respectively. Simulated off-target rates of 2,4-D and dicamba did not influence branching or plant weight at trial termination. In the growth chamber study, the 1× and 1/10× rates of 2,4-D caused 82% and 2% injury 28 DAT, respectively. Plant height, fresh weight, and cannabidiol (CBD) levels of plants treated with simulated off-target rates of 2,4-D were not different from the nontreated control. These studies suggest that hemp grown for CBD exposed to off-target rates of 2,4-D or dicamba in early vegetative stages may not have distinguishable effects 42 DAT or at harvest.

In Mississippi, rice reproduction and ripening often overlaps with soybean maturation, creating potential for herbicide exposure onto rice from desiccants applied to soybeans. Six independent studies were conducted concurrently at the Delta Research and Extension Center in Stoneville, MS, from 2016 to 2018 to determine the response of rice to sublethal concentrations of soybean desiccants during rice reproductive and ripening growth stages. Studies included the desiccants paraquat, glyphosate, saflufenacil, sodium chlorate, paraquat + saflufenacil, and paraquat + sodium chlorate applied at a rate equal to 1/10th of Mississippi recommendations. Treatments were applied at five different rice growth stages, beginning at 50% heading––defined as 0 d after heading (DAH)––with subsequent applications at 1-wk intervals (0, 7, 14, 21, and 28 DAH), up to harvest. Injury was observed 7 d after application (DAA), with five of six desiccants at all application timings. No injury was observed with glyphosate application across all rating intervals. Rough rice grain yield following all glyphosate applications was reduced by >6%. In the studies evaluating paraquat, injury ranged from 5% to 18% at all evaluations, regardless of application timing. Rough rice grain yield was reduced >12% 0 to 21 DAH, following paraquat application. Similar trends were observed with paraquat + saflufenacil and paraquat + sodium chlorate, with rice exhibiting yield decreases >6% following an application 0 to 14 and 0 to 21 DAH, respectively. In studies evaluating saflufenacil and sodium chlorate, rough rice grain yield was >95% of the untreated across all application timings Yield component trends closely resembled reductions observed in rough rice grain yield. Reductions in head rice yield were >5% following applications of paraquat or paraquat + saflufenacil 0 to 14 and 0 to 21 DAH, respectively. Late-season exposure to sublethal concentrations of desiccant from 50% heading (0 DAH) to 28 DAH has an impact on rough rice grain yield, yield components, and head rice yield.

The application of paraquat mixtures with residual herbicides before planting rice is a common treatment in Mississippi, and rice in proximity is susceptible to off-target movement of these applications. Four concurrent studies were conducted in Stoneville, MS, to characterize rice performance following exposure to a sublethal rate of paraquat, metribuzin, fomesafen, and cloransulam-methyl at different application timings. Herbicides were applied to rice at the growth stages of spiking to one-leaf (VEPOST), two- to three-leaf (EPOST), three- to four-leaf (MPOST), 7 d postflood (PFLD), and panicle differentiation (PD). Regardless of application timing, rice injury following exposure to paraquat was ≥45%. Delays in maturity were increased by 0.3 d d−1 following paraquat from emergence through PD. Dry weight, rough rice yield, panicle density, and germination were reduced by 18.7 g, 131.5 kg ha−1, 5.6 m−2, and 0.3%, respectively, per day from application of paraquat at emergence through PD. By 28 d after treatment (DAT), metribuzin injured rice 3% to 6%, and that injury did not translate into a yield reduction. Regardless of application timing, rice injury following fomesafen application ranged from 2% to 5% 28 DAT. Rice exposed to cloransulam-methyl EPOST exhibited the greatest root and foliar injury 21 DAT and 28 DAT, respectively. Additionally, when rice was exposed to cloransulam-methyl EPOST, yield was reduced to 6,540 kg ha−1 compared with a yield of 7,850 kg ha−1 from nontreated rice. Rice yield was negatively affected after paraquat was applied any time after rice emergence. However, applications of paraquat to rice at early reproductive growth stages reduced rough rice yield and seed germination the greatest. Application timing is crucial in determining severity of rice injury. Early-season injury to rice following paraquat application had less effect on yield compared with injury at later stages. Additionally, fields devoted to seed rice production are at risk for reduced seed germination if they are exposed to paraquat during early reproductive growth stages.

Differential tolerance may be observed among rice cultivars with desiccant exposure events during rice reproduction and ripening. Five field studies were established at the Mississippi State University Delta Research and Extension Center in Stoneville, MS, to determine the effects of exposure to sublethal concentrations of common desiccants across multiple rice cultivars. Rice cultivars in the study were ‘CLXL745’, ‘XL753’, ‘CL163’, ‘Rex’, and ‘Jupiter’. Desiccant treatments included no desiccant, paraquat, or glyphosate and were applied at the 50% heading growth stage respective to cultivar. Differential injury estimates among cultivars and desiccant treatments was observed when glyphosate or paraquat was applied at 50% heading. Injury from glyphosate at 50% heading was nondetectable across all cultivars. However, injury following paraquat applications was >7% across all rating intervals and cultivars. Hybrid cultivars exhibited less injury with paraquat applications than the inbred cultivars in the study. Rice following exposure to glyphosate or paraquat at 50% heading growth stage produced rough rice grain yield decreases ranging from 0% to 20% and 9% to 21%, respectively. Rough rice grain yield decreases were observed across all cultivars following paraquat exposure, and all inbred cultivars following glyphosate exposure. Across desiccant treatment, head rice yield was reduced in three of five cultivars in the study. When pooled across cultivar, paraquat applications cause a head rice yield reduction of 10%, whereas rice yield following glyphosate application remained >95%. Although differential tolerance among cultivars to paraquat or glyphosate exposure was observed, impacts on grain quality coupled with yield reductions suggests extreme rice sensitivity to exposure to sublethal concentrations of these desiccants at the 50% heading growth stage.

Off-target paraquat movement to rice has become a major problem in recent years for rice producers in the midsouthern United States. Nitrogen (N) fertilizer is applied to rice in greater quantity and frequency than all other nutrients to optimize rice yield. Two separate field studies were conducted from 2015 to 2018 in Stoneville, MS, to assess whether starter N fertilizer can aid rice recovery from exposure to a sub-lethal concentration of paraquat and to evaluate rice response to different N fertilizer management strategies following exposure to a sub-lethal concentration of paraquat. In both studies, paraquat treatments consisted of paraquat at 0 and 84 g ai ha–1 applied to rice in the two- to three-leaf (EPOST) growth stage. In the starter fertilizer study, N fertilizer at 24 kg ha–1 as ammonium sulfate (AMS) was applied to rice at spiking- to one-leaf (VEPOST), two- to three-leaf (EPOST), or three- to four-leaf (MPOST) growth stages before and after paraquat treatment. In the N fertilizer timing study, N fertilizer at 168 kg N ha–1 was applied in a single four-leaf to one-tiller (LPOST) application or two-, three-, and two four-way split applications. Despite starter N fertilizer applications, paraquat injured rice ≥41%, reduced height 57%, reduced dry weight prior to flooding 77%, delayed maturity 10 d, reduced dry weight at maturity 33%, and reduced rough rice yield 35% in the starter fertilizer study. Similarly, in the N fertilizer timing study, paraquat injured rice ≥45%, reduced height 14%, delayed maturity 10 d, reduced dry weight at maturity 44%, and reduced rough rice yield 50% for all N fertilizer management strategies. Both studies indicate that severe complications in growth and development can occur from rice exposure to a sub-lethal concentration of paraquat. In both studies, manipulation of N fertilizer management did not facilitate rice recovery from early-season exposure to paraquat.

In glyphosate-resistant (GR) cropping systems, paraquat applied in mixtures with residual herbicides prior to crop emergence offers an alternative herbicide mode of action (MOA) to aid in GR weed management. Rice is sensitive to off-target herbicide movement; however, severity of injury can vary with herbicide, rate, and formulation. Therefore, research was conducted from 2015 to 2017 in Stoneville, MS, to characterize rice response to a sublethal concentration of paraquat applied at 84 g ai ha–1 in combination with common residual herbicides. Paraquat plus metribuzin injured rice 68% to 69% 14 and 28 d after treatment (DAT), which was 10% to 13% greater than injury following paraquat alone or paraquat plus fomesafen. Pooled across metribuzin and fomesafen treatments, paraquat reduced rough rice yields 23%. Paraquat plus 10 different residual herbicides injured rice ≥51% 28 DAT and reduced rough rice yields ≥21%. These studies indicate a severe negative impact on rice growth and development following exposure to a sublethal concentration of paraquat alone or in mixture with common residual herbicides. Therefore, applications of paraquat plus residual herbicides to fields in proximity to rice should be avoided if conditions are conducive for off-target movement.

In recent years, unmanned aerial vehicle (UAV) technology has expanded to include UAV sprayers capable of applying pesticides. Very little research has been conducted to optimize application parameters and measure the potential of off-target movement from UAV-based pesticide applications. Field experiments were conducted in Raleigh, NC during spring 2018 to characterize the effect of different application speeds and nozzle types on target area coverage and uniformity of UAV applications. The highest coverage was achieved with an application speed of 1 m s−1 and ranged from 30% to 60%, whereas applications at 7 m s−1 yielded 13% to 22% coverage. Coverage consistently decreased as application speed increased across all nozzles, with extended-range flat-spray nozzles declining at a faster rate than air-induction nozzles, likely due to higher drift. Experiments measuring the drift potential of UAV-applied pesticides using extended-range flat spray, air-induction flat-spray, turbo air–induction flat-spray, and hollow-cone nozzles under 0, 2, 4, 7, and 9 m s−1 perpendicular wind conditions in the immediate 1.75 m above the target were conducted in the absence of natural wind. Off-target movement was observed under all perpendicular wind conditions with all nozzles tested but was nondetectable beyond 5 m away from the target. Coverage from all nozzles exhibited a concave-shaped curve in response to the increasing perpendicular wind speed due to turbulence. The maximum target coverage in drift studies was observed when the perpendicular wind was 0 and 8.94 m s−1, but higher turbulence at the two highest perpendicular wind speeds (6.71 and 8.94 m s−1) increased coverage variability, whereas the lowest variability was observed at 2.24 m s−1 wind speed. Results suggested that air-induction flat-spray and turbo air–induction flat-spray nozzles and an application speed of 3 m s−1 provided an adequate coverage of target areas while minimizing off-target movement risk.

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.

Field studies were conducted in 2009 at Clinton, NC and 2014 at Pontotoc, MS to determine the influence of simulated glyphosate drip on sweetpotato yield and quality. Treatments consisted of three glyphosate solution (140 g ae L–1) drip volumes (0.16, 0.32 and 0.48 ml) by four application timings [(4 wk after transplanting (WAP); 6 WAP; 8 WAP; and 4 WAP followed by (fb) 6 WAP fb 8 WAP]. A non-treated check was included for comparison. Visual sweetpotato injury consisted of chlorosis at the shoot tips approximately 1 wk after treatment fb necrosis and stunting. At 6 WAP and 8 WAP, sweetpotato injury following glyphosate applied 4 WAP was 71 and 65%, respectively. Injury from glyphosate applied 4 WAP fb 6 WAP was 78%. Injury from glyphosate applied 6 WAP was 26% at 8 WAP. In 2009, jumbo, no. 1, canner, and marketable yield of the non-treated check were two to three times greater than glyphosate treatments (0.16, 0.32, 0.48 ml). Likewise, yield of the non-treated check was substantially greater than those treated with 0.16 to 0.48 ml glyphosate solution in 2014. In 2009 and 2014, sweetpotato yield of all grades increased as glyphosate application timing was delayed. In 2009, no. 1 yield from glyphosate 8 WAP (8,210 kg ha–1) was similar to the non-treated check. In 2009, there were no cracked storage roots in the non-treated check. However, sweetpotatoes receiving 0.16 to 0.48 ml glyphosate solution displayed 8 to 17%, 11 to 18%, 5 to 13%, and 11 to 16% cracking (by weight) in jumbo, no. 1, canner, and marketable storage roots, respectively. Compared to the non-treated check, glyphosate applied 4 WAP, 6 WAP, or 4 WAP fb 6 WAP fb 8 WAP had a greater percentage of cracked marketable sweetpotato storage roots.

Applications of aminocyclopyrachlor in 2011 to turf resulted in brown and twisted shoots, leaves, and needles; shoot dieback; and in some cases, death of trees and ornamental plants adjacent to treated turf areas. Our research objective was to determine if a sensitive plant could be injured from wood chips (mulch) obtained from aminocyclopyrachlor-damaged trees, and to quantify movement of aminocyclopyrachlor from contaminated wood chips into soil and its subsequent uptake by roots into landscape plant tissues. Tomatoes were grown under greenhouse conditions and mulched with chipped tree branches collected from honey locust and Norway spruce damaged 12 mo previously by aminocyclopyrachlor. Analysis of tomato tissue for aminocyclopyrachlor residues 32 d after mulching found aminocyclopyrachlor in all mulched tomato plants, which was consistent with observations of epinasty on tomato leaflets. Aminocyclopyrachlor residues ranged from 0.5 to 8.0 ppb in tomato plants while chipped tree branches contained 1.7 to 14.7 ppb. Aminocyclopyrachlor residues in the potting soil below the mulch ranged from below the quantifiable limit to 0.63 ppb, indicating that aminocyclopyrachlor can leach from wood chips into soil, causing plant injury. These results indicate that trees damaged by aminocyclopyrachlor should not be chipped and used for mulch or as an ingredient in compost.