Postemergence (POST) herbicides that control troublesome weeds during hybrid bermudagrass establishment via sprigs are limited due to potential turfgrass phytotoxicity and herbicide-resistant weeds. Research experiments were conducted in Blacksburg, VA, and Hope, AR, in 2016 and 2023 to evaluate herbicide programs to control goosegrass and smooth crabgrass and the response of hybrid bermudagrass sprigs to POST herbicides applied 3 to 5 wk after establishment (WAE). Another study was conducted to assess the tolerance of ‘Latitude 36’, ‘Tahoma 31’, and ‘TifTuf’ hybrid bermudagrass sprigs to POST herbicides applied 4 to 5 WAE. Thiencarbazone + foramsulfuron + halosulfuron did not injure hybrid bermudagrass > 6% across four cultivars and a total of 10 site-yr but reduced goosegrass and smooth crabgrass cover equivalent to the best-performing treatments. Topramezone + metribuzin injured turfgrass > 25% at 14 d after treatment (DAT), but tank mixing with thiencarbazone + foramsulfuron + halosulfuron reduced injury by 5% to 22%. Quinclorac injured hybrid bermudagrass 17% to 58%, depending on site, which was more than most other treatments. Mesotrione-, quinclorac-, or topramezone-based programs injured hybrid bermudagrass and also reduced turfgrass cover, the dark green color index, and the normalized difference vegetation index, but turfgrass recovered by 28 DAT. Results suggest that turfgrass managers have a variety of herbicides that can control smooth crabgrass and goosegrass during hybrid bermudagrass sprig establishment, but the margin of selectivity is relatively low for mesotrione, quinclorac, and topramezone and may be dependent on herbicide rate or hybrid bermudagrass cultivar.

Amaranthus species are problematic weeds in snap bean production systems. They reduce crop yields, and their stem fragments contaminate harvested pods. Knowledge of snap bean tolerance to different preemergence herbicides is limited; however, knowing this tolerance is essential for planning a reliable weed management system, breeding herbicide-tolerant cultivars, and registering herbicides for use on minor crops such as snap bean. Field trials were conducted in 2021 and 2022 to determine the tolerance of eight snap bean cultivars to preemergence herbicides with activity on Amaranthus species, including dimethenamid-P, flumioxazin, lactofen, metribuzin, saflufenacil, and sulfentrazone. Snap bean plant density (number of plants per square meter), plant biomass (grams per plant), and canopy biomass (grams per square meter) 21 d after treatment were used to assess crop tolerance to a range of herbicide rates. Linear mixed-effects regression models were fitted to quantify the relationships between preemergence herbicide rate and snap bean cultivar tolerance. Results indicated a high margin of crop safety with dimethenamid-P and lactofen for weed control in snap bean, and a low margin of crop safety with metribuzin and saflufenacil. Results indicated differential cultivar tolerance to flumioxazin and sulfentrazone, which could be driven by genetic variability among cultivars.

Amicarbazone, atrazine, and metribuzin behavior was examined in a field setting in Tennessee and in a laboratory setting using soils collected from Illinois and Tennessee. Fields planted to corn were sampled from 0 to 8 cm depth, and the samples were analyzed using methanolic extraction followed by tandem mass spectrometry analysis to determine residual herbicide concentrations. Conditions were favorable for herbicide degradation, including warm temperatures and adequate rainfall. All herbicide half-lives were <10 d. Laboratory research using soils with known atrazine-use histories showed that amicarbazone did not exhibit enhanced microbial degradation due to previous atrazine use. Apparent amicarbazone and metribuzin persistence levels implied that early-season weed control would be expected, but carryover to injure sensitive rotational crops would not be anticipated under these environmental conditions. Dissipation under field conditions of amicarbazone and metribuzin was not affected by being applied to separate plots or by coapplication to the same plots.

Tiafenacil is a new nonselective protoporphyrinogen IX oxidase–inhibiting herbicide with both grass and broadleaf activity labeled for preplant application to corn, cotton, soybean, and wheat. Early season rice emergence and growth often coincide in the mid-southern United States with applications of preplant herbicides to cotton and soybean, thereby increasing the opportunity for off-target herbicide movement from adjacent fields. Field studies were conducted to identify any deleterious effects of reduced rates of tiafenacil (12.5% to 0.4% of the lowest labeled application rate of 24.64 g ai ha−1) applied to 1- or 3-leaf rice. Visual injury 1 wk after treatment (WAT) for the 1- and 3-leaf growth stages ranged from 50% to 7% and 20% to 2%, respectively, whereas at 2 WAT these respective ranges were 13% to 2%, and no injury was observed. Tiafenacil applied at those rates had no negative season-long effect because observed early season injury was not manifested as a reduction in rice height 2 WAT or rough rice yield. Application of tiafenacil to crops directly adjacent to rice in its early vegetative stages of growth should be avoided because visual injury will occur. When off-target movement does occur, however, the affected rice should be expected to fully recover with no effect on growth or yield, assuming adequate growing conditions and agronomic/pest management are provided.

Georgia growers can benefit from double-cropping grain sorghum following watermelon to maximize land use and add economic value to their operations. However, capitalizing on the economic advantages of harvesting two crops within a single season must account for potential herbicide injury to rotational crops. An integrated weed management strategy that includes a preplant application of fomesafen and terbacil is recommended for weed control in watermelon production systems. However, currently labeled plant-back restrictions for grain sorghum require a minimum of 10 and 24 mo for fomesafen and terbacil, respectively. Therefore this research aimed to determine the tolerance of grain sorghum to fomesafen and terbacil following soil applications applied 90 to 100 d before planting (DBP). Experiments were conducted at the University of Georgia Ponder Research Farm from 2019 to 2023. The experimental design was a randomized complete block with four replicates. Five rates of fomesafen (35, 70, 140, 210, and 280 g ai ha−1), four rates of terbacil (3.5, 7.0, 10.5, and 14.0 g ai ha−1), and a nontreated control were evaluated. In 2019, fomesafen caused significant sorghum leaf necrosis, plant density reductions, height reductions, and yield reductions of at least 16%, especially when applied at rates ≥ 210 g ai ha−1. Terbacil had little to no effect on sorghum injury, density, height, or yield in any year. These results suggest that sorghum has sufficient tolerance to terbacil when applied 90 to 100 DBP. In four of five years, sorghum had an acceptable tolerance to fomesafen when applied 90 to 100 DBP. However, yield losses observed in 2019 suggest that caution should be taken when fomesafen is applied 90 to 100 DBP grain sorghum at ≥ 210 g ai ha−1.

Benghal dayflower and sicklepod are weeds of economic importance in peanut in the southeastern United States due to their extended emergence pattern and limited effective herbicides for control. Field studies were conducted near Jay, Florida, in 2022 and 2023, to evaluate the effect of planting date and herbicide combinations on Benghal dayflower and sicklepod control in peanut crops. Peanut planted in June was exposed to a higher Benghal dayflower density than peanut planted in May. Sicklepod density was similar between May and June planting dates at 28 d after preemergence and early postemergence herbicide applications, but density was greater in peanut that was planted in June, 28 d after the mid-postemergence application. A preemeergence herbicide application followed by (fb) an early postemergence application of S-metolachlor or diclosulam + S-metolachlor controlled Benghal dayflower 84% to 93% 28 d after early postemergence in peanut that was planted in May, but control was reduced to 58% to 78% in the crop that had been planted in June. Regardless of planting date, a preemeergence application fb S-metolachlor or diclosulam + S-metolachlor applied early postemergence provided <80% sicklepod control 28 d after early postemergence. Imazapic + dimethenamid-P + 2,4-DB applied postemergence improved Benghal dayflower control to at least 94% 28 d after mid-postemergence, but sicklepod control was not >85%. Regardless of the planting date, paraquat + bentazon + S-metolachlor applied early postemergence was required to achieve ≥95% sicklepod control. However, herbicide combinations that included paraquat + bentazon + S-metolachlor reduced peanut yield when planting was delayed to June. In fields that are infested with Benghal dayflower and sicklepod, it is recommended that peanut be planted in early May to minimize the potential impact of these weeds and to increase peanut yield. Late-planted peanut required more intensive herbicide applications to obtain the same peanut yield as the May-planted peanut.

Rice herbicide drift poses a significant challenge in California, where rice fields are near almond, pistachio, and walnut orchards. This research was conducted as part of a stewardship program for a newly registered rice herbicide and specifically aimed to compare the onset of foliar symptoms resulting from simulated florpyrauxifen-benzyl drift with residues in almond, pistachio, and walnut leaves at several time points after exposure. Treatments were applied to one side of the canopy of 1- and 2-yr-old trees at 1/100X and 1/33X of the florpyrauxifen-benzyl rice field use rate of 29.4 g ai ha–1 in 2020 and 2021. Symptoms were observed 3 d after treatment (DAT) for pistachio and 7 DAT for almond and walnut, with peak severity at approximately 14 DAT. While almond and walnut symptoms gradually dissipated throughout the growing season, pistachio still had symptoms at leaf out in the following spring. Leaf samples were randomly collected from each tree for residue analysis at 7, 14, and 28 DAT. At 7 DAT with the 1/33X rate, almond, pistachio, and walnut leaves had florpyrauxifen-benzyl at 6.06, 5.95, and 13.12 ng g–1 fresh weight (FW) leaf, respectively. By 28 DAT, all samples from all crops treated with the 1/33X drift rate had florpyrauxifen-benzyl at less than 0.25 ng g–1 FW leaf. At the 1/100X rate, pistachio, almond, and walnut residues were 1.78, 2.31, and 3.58 ng g–1 FW leaf at 7 DAT, respectively. At 28 DAT with the 1/100X rate, pistachio and almond samples had florpyrauxifen-benzyl at 0.1 and 0.04 ng g–1 FW leaf, respectively, but walnut leaves did not have detectable residues. Together, these data suggest that residue analysis from leaf samples collected after severe symptoms may substantially underestimate actual exposure due to the relatively rapid dissipation of florpyrauxifen-benzyl in nut tree foliage.

Deertongue is a perennial, warm-season grass, and is problematic in naturalized areas of golf courses due to limited control options. Research was conducted to evaluate several herbicides for deertongue control in naturalized areas consisting primarily of fine fescue. Greenhouse studies assessed 24 herbicide admixtures and indicated that fluazifop, glyphosate, imazapic, and thiencarbazone + iodosulfuron + dicamba (TID) reduced deertongue biomass by >80% at 10 wk after initial treatment (WAIT). Subsequent field trials were conducted on golf course naturalized areas. The first site was on a woodland edge and was partially shaded for 6 h each day, and the second trial site was 50 m away from the woodland edge and not subjected to more than 1 h of daily shade. At 9 WAIT, fluazifop at 420 g ai ha−1 applied once or three times at 3-wk intervals and topramezone at 37 g ai ha−1 applied thrice at 3-wk intervals injured fine fescue by ≤10% at both sites. Glyphosate applied at 1,120 g ae ha−1, imazapic at 105 g ai ha−1, and imazapic at 53 g ai ha−1 tank-mixed with glyphosate at 560 g ae ha−1 injured fine fescue by ≥50% under shaded conditions, whereas glyphosate alone did not injure fine fescue under sunny conditions. Fine fescue was completely recovered by 52 WAIT from injury following herbicide treatments, except for glyphosate-containing treatments at the shaded site and glyphosate + imazapic at both sites. At 52 WAIT, glyphosate-containing treatments and sequential applications of fluazifop controlled deertongue by ≥93% and reduced shoot density to ≤5 shoots m−2 averaged over both sites. Fluazifop at 420 g ha−1 applied thrice at 3-wk intervals selectively controls deertongue with excellent safety to fine fescue. Glyphosate also controls deertongue, but unacceptably injures fine fescue when managed under shaded conditions. Future research will assess how different light intensities influence fine fescue epicuticular wax deposits and associated response to glyphosate.

Waterhemp is a dioecious species with wide genetic diversity which has enabled it to evolve resistance to several commonly used herbicide groups in North America. Five field trials were established in Ontario to ascertain the biologically effective doses of diflufenican, a new Group 12 herbicide applied preemergence for control of multiple herbicide–resistant (MHR) waterhemp in corn. Based on regression analysis, the predicted diflufenican doses to elicit 50%, 80%, and 95% MHR waterhemp control were 99, 225, and 417 g ai ha−1, respectively, at 2 wk after application (WAA); 73, 169, and 314 g ai ha−1, respectively, at 4 WAA; and 76, 215, and — (meaning the effective dose was beyond the set of doses in this study) g ai ha−1, respectively, at 8 WAA. The predicted diflufenican doses that would cause a 50%, 80%, and 95% decreases in MHR waterhemp density were 42, 123, and — g ai ha−1; and MHR waterhemp biomass were 72, 167, and 310 g ai ha−1, respectively, at 8 WAA. Diflufenican applied preemergence at 150 g ai ha−1 controlled MHR waterhemp by 64%, 79%, and 73% at 2, 4, and 8 WAA, respectively. Isoxaflutole + atrazine applied preemergence at 105 + 1,060 g ai ha−1 controlled MHR waterhemp by 98%, 98%, and 97% at 2, 4, and 8 WAA, respectively; and S-metolachlor/mesotrione/bicyclopyrone/atrazine applied preemergence at 1,259/140/35/588 g ai ha−1 controlled MHR waterhemp by 100%, 100%, and 99% at 2, 4, and 8 WAA, respectively. Diflufenican applied preemergence reduced MHR waterhemp density and biomass by 83%; in contrast, isoxaflutole + atrazine and S-metolachlor/mesotrione/bicyclopyrone/atrazine reduced MHR waterhemp density and biomass by 99%. All treatments evaluated caused either no, or minimal, corn injury and resulted in corn yield that was similar with the weed-free control. Results indicate that diflufenican applied alone preemergence does not provide superior MHR waterhemp control over the commonly used herbicides isoxaflutole + atrazine or S-metolachlor/mesotrione/bicyclopyrone/atrazine; however, there is potential for using diflufenican as part of an integrated weed management strategy for the control of MHR waterhemp control in corn.

Khakiweed is a perennial broadleaf weed that is difficult to control because of its multiple means of reproduction, vigorous growth, and deep taproot. Khakiweed reduces the performance of pasture, pecan, and turf areas by choking out desirable grass and legume species. Because information on the effectiveness of contact and residual herbicides for control in pecan and pasture areas is limited, greenhouse studies were conducted to determine the effect of application timing, mode of action, and rate on khakiweed control. Preemergence and postemergence herbicides were applied to mature khakiweed plants at 0.25X, 0.5X, 1X, or 2X the label recommended rate for general broadleaf control. Biomass was collected 3 wk after application. Plants regrew from roots in the greenhouse until a second biomass harvest was collected at 6 wk after treatment (WAT). Metsulfuron-methyl, indaziflam, or pendimethalin was applied preemergence to the soil surface. All rates of preemergence herbicides provided high-efficacy control of regrowth (>85%) compared to the nontreated control. The efficacies of postemergence-applied metsulfuron-methyl, metsulfuron-methyl + nicosulfuron, indaziflam, aminopyralid + florpyrauxifen-benzyl, 2,4-D amine, and 2,4-D amine + florpyrauxifen-benzyl were also examined. All postemergence herbicide treatments exhibited control compared to the nontreated plants at both sample timings (3 and 6 WAT) and increased with herbicide application rate. No herbicide provided high-efficacy control during the initial postspray period (0 to 3 WAT). During the regrowth period (3 to 6 WAT), metsulfuron-methyl alone and in combination gave >85% control of khakiweed biomass, indicating that the sulfonylurea herbicides used in this study are well suited to controlling khakiweed.

All field scientists involved with weed management understand the importance of accurate weed identification and appreciate the need for widely recognized common names. USDA played a pivotal and critical role with the effort to advance our discipline while weed science was in its infancy.

Two separate field studies were conducted at two locations near Crowley, Louisiana, to evaluate early season applications of florpyrauxifen and a prepackaged mixture of halosulfuron plus prosulfuron in water-seeded rice production. In each study, florpyrauxifen and halosulfuron plus prosulfuron were applied at two rates and either applied to the soil surface 48 h before the seeding flooding and seeding, directly onto the pregerminated seed 24 h following seeding and immediately after removal of the seeding flood (SEED), and at pegging. Data suggest that both florpyrauxifen and halosulfuron plus prosulfuron have a role to play in water-seeded rice production. Crop injury of 19% was observed from applications of florpyrauxifen applied directly to pregerminated SEED. Additionally, 28% crop injury was observed when halosulfuron plus prosulfuron was applied directly to SEED. Due to crop injury observations, both herbicides should be avoided when the pregerminated seed is exposed to the soil surface after removing the seeding flood. These data suggest that florpyrauxifen may be a better option for postemergence application, whereas halosulfuron plus prosulfuron may be a better preemergence option in water-seeded rice production. Overall, the findings show that both herbicide technologies will provide adequate early-season weed control in water-seeded rice production.

Cover crop adoption is increasing among growers with the occurrence of herbicide-resistant weed species. A field study conducted at three sites from autumn 2021 through the crop harvest in 2022 in Alabama aimed to evaluate the combined effect of cover crop residue and herbicides for weed control and improved cotton lint yield. The experiment was conducted in split-plot design with main plots consisting of six cover crop treatments: cereal rye, crimson clover, oat, radish, cover crop mixture, and winter fallow. The subplots included four herbicide treatments: (i) preemergence, pendimethalin + fomesafen, (ii) postemergence, dicamba + glyphosate + S-metolachlor, (iii) preemergence followed by postemergence, and (iv) nontreated (NT) check. Cover crops, excluding radish, exhibited greater weed biomass reduction than winter fallow with corresponding herbicide treatments of either preemergence, postemergence, or preemergence + postemergence as compared to control (winter fallow and NT check). Considering preemergence + postemergence treatment, cereal rye, crimson clover, oat, and cover crop mixture provided >95% weed biomass reduction as compared to control. Looking at the overall effect of cover crop, cereal rye outperformed and showed greater weed biomass reduction than radish relative to control. Preemergence + postemergence herbicide treatment resulted in greater lint yield than other treatments. Cotton in cereal rye plots had a greater lint yield than in winter fallow at one out of three locations. In conclusion, integrating herbicides and incorporating high-residue cover crops such as cereal rye is an effective weed management strategy to control troublesome weeds.

New machine-vision technologies like the John Deere See & Spray™ could provide the opportunity to reduce herbicide use by detecting weeds and target-spraying herbicides simultaneously. Experiments were conducted for 2 yr in Keiser, AR, and Greenville, MS, to compare residual herbicide timings and targeted spray applications versus traditional broadcast herbicide programs in glyphosate/glufosinate/dicamba-resistant soybean. Treatments utilized consistent herbicides and rates with a preemergence (PRE) application followed by an early postemergence (EPOST) dicamba application followed by a mid-postemergence (MPOST) glufosinate application. All treatments included a residual at PRE and excluded or included a residual EPOST and MPOST. Additionally, the herbicide application method was considered, with traditional broadcast applications, broadcasted residual + targeted applications of postemergence herbicides (dual tank), or targeted applications of all herbicides (single tank). Targeted applications provided comparable control to broadcast applications with a ≤1% decrease in efficacy and overall control ≥93% for Palmer amaranth, broadleaf signalgrass, morningglory species, and purslane species. Additionally, targeted sprays slightly reduced soybean injury by at most 5 percentage points across all evaluations, and these effects did not translate to a yield increase at harvest. The relationship between weed area and targeted sprayed area also indicates that nozzle angle can influence potential herbicide savings, with narrower nozzle angles spraying less area. On average, targeted sprays saved a range of 28.4% to 62.4% on postemergence herbicides. On the basis of these results, with specific machine settings, targeted application programs could reduce the amount of herbicide applied while providing weed control comparable to that of traditional broadcast applications.

Field experiments were conducted at Clayton and Rocky Mount, NC, during summer 2020 to determine the growth and fecundity of Palmer amaranth plants that survived glufosinate with and without grass competition in cotton. Glufosinate (590 g ai ha−1) was applied to Palmer amaranth early postemergence (5 cm tall), mid-postemergence (7 to 10 cm tall), and late postemergence (>10 cm tall) and at orthogonal combinations of those timings. Nontreated Palmer amaranth was grown in weedy, weed-free in-crop (WFIC) and weed-free fallow (WFNC) conditions for comparisons. Palmer amaranth control decreased as larger plants were treated; no plants survived the sequential glufosinate applications in both experiments. The apical and circumferential growth of Palmer amaranth surviving glufosinate treatments was reduced by more than 44% compared to the WFIC and WFNC Palmer amaranth in both experiments. The biomass of Palmer amaranth plants surviving glufosinate was reduced by more than 62% when compared with the WFIC and WFNC in all experiments. The fecundity of Palmer amaranth surviving glufosinate treatments was reduced by more than 73% compared to WFNC Palmer amaranth in all experiments. Remarkably, the plants that survived glufosinate were fecund as WFIC plants only in the Grass Competition experiment. The results prove that despite decreased vegetative growth of Palmer amaranth surviving glufosinate treatment, plants remain fecund and can be fecund as nontreated plants in cotton. These results suggest that a glufosinate-treated grass weed may not have a significant interspecific competition effect on Palmer amaranth that survives glufosinate. Glufosinate should be applied to 5 to 7 cm Palmer amaranth to cease vegetative and reproductive capacities.

Annual bluegrass is one of the most problematic weeds in the turfgrass industry, exhibiting both cross-resistance and multiple-herbicide resistance. Prodiamine, pronamide, and indaziflam are commonly used preemergence herbicides for the control of this species on golf courses in the southern United States. There have been increasing anecdotal reports of annual bluegrass populations escaping control with these herbicides, but resistance has yet to be confirmed. To evaluate the response of annual bluegrass to three herbicides, populations were collected from golf courses, athletic fields, and landscape areas in Texas and Florida, and a dose-response assay was conducted on populations that were suspected to be resistant to and known to be susceptible to prodiamine, pronamide, and indaziflam. The suspected-resistant populations showed survival to prodiamine at 32 times the recommended field rate (both populations from Florida and Texas) of 736 g ai ha−1, and to pronamide at 32 times (the Florida populations) or 16 times (the Texas populations) the recommended field rate of 1,156 g ha−1. In contrast, the known susceptible populations attained 100% mortality at rates as low as 46 and 578 g ha−1, respectively, from applications of prodiamine and pronamide. For indaziflam, the suspected-resistant populations showed reduced sensitivity up to the recommended field rate of 55 g ha−1, but they were controlled when treated with a rate twice that of the field rate. Overall, annual bluegrass populations with resistance to prodiamine and pronamide, and reduced sensitivity to indaziflam (at the recommended field rate) were confirmed from golf courses in Florida and Texas. In the presence of herbicide-resistant annual bluegrass populations, especially to commonly used herbicides such as prodiamine and pronamide, turfgrass managers should adopt integrated management strategies and frequently rotate herbicide sites of action, rather than relying solely on microtubule-assembly inhibitors or cellulose biosynthesis inhibitors, to control this species.

Carolina redroot (LAHTI) is a perennial weed of New Jersey cranberry beds. It is associated with “stand opening” areas that result from fairy ring dieback or other conditions of natural and anthropogenic origin. LAHTI accounts for significant yield reduction through direct competition with cranberry for nutritional resources. Field experiments were conducted from 2017 to 2022 on ‘Ben Lear’ and ‘Early Black’ cranberry beds in Chatsworth, NJ, to determine 1) the efficacy of residual herbicides labeled for use on cranberry, and subsequently, 2) to evaluate the value of overlapping preemergence applications of napropamide and postemergence applications of mesotrione for LAHTI control while minimizing crop phytotoxicity. Treatments in the first experiment included preemergence applications of dichlobenil or norflurazon at 2.2 and 4.5 kg ha−1 and napropamide a 6.7 kg ha−1. In the second trial, napropamide was applied preemergence annually to plots at 6.7 or 10.1 kg ha−1 either as a single or as two equally or unequally split applications spaced 30 d apart, followed by or not followed by mesotrione applied postemergence at 280 g ha−1 when LAHTI leaves emerged above the cranberry canopy. The preemergence herbicides dichlobenil applied at 4.5 kg ha−1 and napropamide provided ≥48% LAHTI control and ≥40% LAHTI biomass reduction 112 d after treatment (DAT), whereas norflurazon had no significant effect on LAHTI biomass. Less than 4% of crop injury and liquid formulation adapted to chemigation identified napropamide as an effective preemergence herbicide for LAHTI control. In the second trial, napropamide applied at 10.1 kg ha−1 followed by an application of mesotrione reduced LAHTI biomass by ≥73%. Splitting napropamide application reduced yield by 36% and berry weight by 12% compared with a single application at the dormant stage. Compared with the nontreated control, a single napropamide application at 10.1 kg ha−1 followed by an application of mesotrione increased yield by 38%. Information derived from these studies is already being used by growers to enhance the productivity and profitability of New Jersey cranberry fields.

Tiafenacil is a new nonselective protoporphyrinogen IX oxidase (PPO)–inhibiting herbicide with both grass and broadleaf activity labeled for preplant application to corn, cotton, soybean, and wheat. Early-season corn emergence and growth often coincides in the mid-South with preplant herbicide application in cotton and soybean, thereby increasing opportunity for off-target herbicide movement from adjacent fields. Field studies were conducted in 2022 to identify the impacts of reduced rates of tiafenacil (12.5% to 0.4% of the lowest labeled application rate of 24.64 g ai ha–1) applied to two- or four-leaf corn. Corn injury 1 wk after treatment (WAT) for the two- and four-leaf growth stages ranged from 31% to 6% and 37% to 9%, respectively, whereas at 2 WAT these respective ranges were 21.7% to 4% and 22.5% to 7.2%. By 4 WAT, visible injury following the two- and four-leaf exposure timing was no greater than 8% in all instances except the highest tiafenacil rate applied at the four-leaf growth stage (13%). Tiafenacil had no negative season-long impact, as the early-season injury observed was not manifested in a reduction in corn height 2 WAT or yield. Application of tiafenacil directly adjacent to corn in early vegetative stages of growth should be avoided. In cases where off-target movement does occur, however, affected corn should be expected to fully recover with no impact on growth and yield, assuming adequate growing conditions and agronomic/pest management practices are provided.

Commercialization of florpyrauxifen-benzyl as Loyant® in 2018 as a synthetic auxin herbicide in rice was followed by soybean injury due to off-target movement of spray applications in the mid-southern United States. Concerns surrounding off-target movement led to the exploration of an alternative application method to help alleviate the issue. Field experiments were conducted in 2020 and 2021 to explore the likelihood of a reduction in soybean injury following applications of florpyrauxifen-benzyl coated on urea in narrow- and wide-row soybean systems and to determine the likelihood of volatilization from this novel application method. Florpyrauxifen-benzyl spray-applied at 0.18 g ai ha−1 caused greater than 60% injury, whereas coating the herbicide on urea at 5.63 g ai ha−1 never exceeded 30% injury in narrow-row soybean. Similarly, florpyrauxifen-benzyl spray-applied at 0.18 g ai ha−1 caused greater than 50% injury, whereas coating the herbicide on urea at 5.63 g ai ha−1 never exceeded 30% injury in wide-row soybean. As soybean injury increased, relative yield decreased in both narrow- and wide-row soybean. Spray-applied florpyrauxifen-benzyl decreased relative soybean groundcover, yield components, and soybean survival rate as the herbicide rate increased, whereas coating the herbicide on urea resulted in little to no decrease in both narrow- and wide-row soybean assessments. No negative impacts on relative yield and yield components of soybean from florpyrauxifen-benzyl coated on urea indicates that even though visible injury may persist, there is a low likelihood of any yield losses associated with the herbicide exposure using this application method. Additionally, coating the florpyrauxifen-benzyl on urea did not increase the likelihood of volatilization under any of the evaluated soil moisture conditions. Overall, applying florpyrauxifen-benzyl coated on urea is likely to be a safer application method and can reduce soybean injury compared to spray-applying the herbicide when favorable off-target movement conditions exist.

Several publications and web-based tools are available in weed science literature to help weed scientists to carry out basic analysis of dose-response studies. Given the nature of the complicated relationship between the explanatory variable (dose as x-axis) evaluated against response variables of interest (y-axis), using regression curves should be the preferred method for handling data analysis. The objective of this manuscript is to provide user-friendly instructions for conducting and analyzing several types of dose-response studies that were lacking in current weed science literature. A better understanding of less commonly used concepts of hormesis and toxicological safety thresholds (no-observable-adverse-effect-level [NOAEL] and lowest-observable-adverse-effect-level [LOAEL]) is needed to help address the potential risks and benefits associated with herbicide use while minimizing environmental impacts. Basic codes available in cost-free R software are provided for data analysis and to foster collaboration among weed scientists.