Tiafenacil is a new non-selective protoporphyrinogen IX oxidase (PPO)-inhibiting herbicide with both grass and broadleaf activity labeled for preplant application to corn (Zea mays L.), cotton (Gossypium hirsutum L.), soybean [Glycine max (L.) Merr.], and wheat (Triticum aestivum L.). Early-season soybean emergence and growth often coincide in the U.S. Midsouth with preplant herbicide application in later-planted cotton and soybean, thereby increasing opportunity for off-target herbicide movement from adjacent fields. Field studies were conducted in 2022 to identify any deleterious 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 1- to 2-leaf soybean. Visual injury at 1 wk after treatment (WAT) with 1/8×, 1/16×, 1/32×, and 1/64× rate of tiafenacil was 80%, 61%, 39%, and 21%, while at 4 WAT, these respective rates resulted in visual injury of 67%, 33%, 14%, and 4%. Tiafenacil at these respective rates reduced soybean height 55% to 2% and 53% to 5% at 1 and 4 WAT and soybean yield 53%, 24%, 5%, and 1%. Application of tiafenacil directly adjacent to soybean in early vegetative growth should be avoided, as severe visual injury will occur. In cases where off-target movement does occur, impacted soybean should not be expected to fully recover, and negative impact on growth and yield will be observed.

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.

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.

The herbicide dicamba has injured millions of hectares of sensitive plant species in the United States since 2017. This injury has coincided with the commercialization of dicamba-resistant soybean [Glycine max (L.) Merr.] and cotton (Gossypium hirsutum L.). We quantified atmospheric deposition and mass flux of dicamba in 12 soybean production regions of Missouri. Dicamba was routinely detected in weekly deposition samples collected during agriculturally intensive spray periods. Observed concentrations were indicative of both local (<1 km) and long-distance transport (>1 km) of airborne dicamba. High-deposition events (>100 µg m−2) occurred annually in southeast Missouri, and peak dicamba deposited at these sites (12.5 to 84.0 µg m−2) was sufficient to injure non–dicamba resistant soybean. Adoption rate of dicamba-resistant crops and atmospheric stability explained much of the variance, and it is difficult for a herbicide product label to address these variables. Overall, these results demonstrated that dicamba was commonly deposited from the atmosphere during the growing season, and observed concentrations and fluxes were strongly related to the timing and magnitude of rainfall events and the amount of dicamba usage near collection sites.

In New Mexico chile pepper production, pendimethalin is traditionally applied shortly after crop thinning, which is 9 to 10 wk after crop seeding. Pendimethalin applications before crop thinning may be a method for controlling early-season weeds in chile pepper; however, chile pepper tolerance to early-season applications of pendimethalin is poorly understood. We conducted a greenhouse study to evaluate young chile pepper responses to pendimethalin. We also conducted a field study to determine weed and chile pepper responses to early-season, postemergence-directed pendimethalin in combination with herbicides registered for preemergence applications. The greenhouse study included three treatments administered when chile pepper was at the four-leaf stage: (i) pendimethalin applied to foliage and soil, (ii) pendimethalin applied to soil only, and (iii) a nontreated control. The field study included four treatments: (i) preemergence applications of napropamide followed by postemergence-directed pendimethalin at 5 wk after crop seeding, (ii) preemergence applications of clomazone followed by postemergence-directed pendimethalin at 5 wk after crop seeding, (iii) postemergence-directed pendimethalin without preemergence herbicides, and (iv) nontreated, weed-free control. We conducted the field study at two sites that differed in soil texture. Pendimethalin application rates were maximum labeled rates for the specific soil. Results from the greenhouse study indicated that pendimethalin applied to foliage and soil stunted two of five cultivars, whereas pendimethalin applied to soil did not affect chile pepper height, fresh weight, dry weight, or root area. Results from the field study indicated that postemergence-directed pendimethalin did not affect chile pepper height or fruit yield, or cause visible symptoms of herbicide injury. Postemergence-directed pendimethalin reduced the densities of weeds, including junglerice. The results of this study indicate that postemergence-directed applications of pendimethalin at 5 wk after crop seeding do not cause crop injury or yield loss in chile pepper, while providing some weed control benefits.

Two low-dose dicamba exposure trials were conducted on container-grown peach trees in Fayetteville, AR. Peach trees were ‘July Prince’ scions grafted onto ‘Guardian’ rootstock, were transplanted into 19-L containers, and received experimental dicamba treatments in each year. Container trials were initiated in 2020 and repeated on new trees in 2021. In the repeated application trial, dicamba was applied at 5.6 g ae ha−1 (1/100X field rate) in five sequences: an untreated control receiving no herbicide, one treatment receiving only an initial application, and three treatments receiving an initial application plus sequential applications at the same rate occurring at 14 d, 28 d, and 14 d + 28 d after initial treatment (DAT). A separate trial assessed peach tree responses to dicamba applied at 11.2 g ae ha−1 (1/50X field rate) using a selection of nozzles with differing droplet spectrum characteristics: Turbo TeeJet® induction nozzle TTI11002, air induction turbo TwinJet® nozzle AITTJ60-11002, air induction extended-range (XR) TeeJet® nozzle AIXR11002, XR TeeJet® flat-fan nozzle XR11002, and XR TeeJet® flat-fan nozzle XR1100067. Peach tree height, tree cross-sectional area, and leaf chlorophyll content were not reduced in response to any sequence of dicamba application or nozzle selection. Repeated applications of dicamba at a 1/100X rate did not increase peach injury after 28 DAT. By 84 DAT, no effect of nozzle type on peach tree injury was discernable, and all treatments caused below 4% injury. No dicamba or dicamba metabolites were observed in leaf samples collected at 14, 69, or 85 DAT from trees treated with XR1100067 or in untreated controls. While peach tree injury was observed throughout the experiment, dicamba residues were detected consistently only in 2020 from leaf samples of trees treated with dicamba at a 1/50X rate using TTI1102, AITTJ60-11002, AIXR11002, and XR11002 nozzles.

In 2021 and 2022, research was initiated at two locations to evaluate the efficacy and safety of sulfentrazone in transplanted cabbage and broccoli. Treatments included oxyfluorfen at 560 g ha−1 applied pretransplant (PRE-T), sulfentrazone applied at 116 or 233 g ha−1 PRE-T, and S-metolachlor applied at 715 g ha−1 immediately after transplanting (POST-T) followed by (fb) oxyfluorfen applied at 210 g ha−1 postemergence (POST) 14 d after planting (DAP). The weedy cover of nontreated plots averaged between 6% (14 DAP) and 72% (42 DAP); all herbicide-treated plots averaged less than 30% cover at 42 DAP. At 14 and 28 DAP, oxyfluorfen, S–metolachlor fb oxyfluorfen, and the high rate of sulfentrazone reduced total monocotyledonous and dicotyledonous weed densities by 62% and 100%, respectively, relative to the nontreated control. The density of hairy galinsoga (in New Jersey) and combined ladysthumb and prostrate knotweed (in New York) were reduced by 71% to 99%. Except for the low rate of sulfentrazone, all herbicide treatments reduced weed biomass at harvest by ≥88%. Crop injury varied in response to herbicide treatments or weed competition but was also affected by crop and location. Between 14 and 28 DAP, the greatest amount of stunting (22%) was noted in the S-metolachlor fb oxyfluorfen treatments at both locations. Averaged over treatments, greater stunting was observed in broccoli than in cabbage in New York, whereas stunting estimates were higher for cabbage in New Jersey. All treatments in New Jersey resulted in significantly increased cabbage yield and broccoli and cabbage head sizes relative to the nontreated controls. No yield difference was noted between herbicide treatments and the nontreated check in New York. Data derived from these studies will be used to enhance crop safety recommendations in northeastern U.S. production environments for sulfentrazone used PRE in transplanted cabbage and support a potential label for broccoli.

More growers across the U.S. Midwest are considering interseeding or overseeding cover crops into corn for soil health purposes. One challenge of this practice is the potential injury from soil residual herbicides applied preemergence (PRE) for weed control in corn to the interseeded and overseeded cover crop species. Field-treated soil was collected in 2021 and 2022 at Janesville, WI, and Lancaster, WI, to investigate the impact of PRE residual herbicides on establishment of interseeded and overseeded cover crops via greenhouse bioassay. Soil samples (0 to 5 cm depth) were collected from field experiments at 0, 10, 20, 30, 40, 50, 60, and 70 days after treatment (DAT). Treatments consisted of 14 single and multiple sites of action (SOAs) PRE herbicides plus a nontreated check (NTC). Four bioindicator cover crop species were used in the greenhouse bioassay: annual ryegrass, cereal rye, radish, and red clover. Cover crop biomass was collected 28 d after bioassay seeding. Cover crop species responded differently across herbicide treatments. Annual ryegrass and cereal rye were sensitive to treatments containing herbicide Group 15, whereas Groups 2, 4, 5, 14, and 27 had minimal impact on their establishment when field soil was collected at 30 DAT (interseeding scenario) and 70 DAT (overseeding scenario) compared to the NTC. Radish and red clover were sensitive to herbicide Groups 2, 4, and 27, whereas Groups 5, 14, and 15 had minimal impact on their establishment. Annual ryegrass, radish, and red clover were more sensitive to PRE herbicides containing two and three SOAs than to herbicides with a single SOA. On the basis of these greenhouse bioassay results, cover crop species should be carefully selected depending on the soil residual herbicide when interseeded and overseeded into corn. Field studies will be conducted to validate these results and support recommendations to growers interested in this system.

Following the introduction of dicamba-resistant (DR) soybean in 2017, concerns have increased with regard to dicamba off-target movement (OTM) onto sensitive crops, including vegetables. Field trials were conducted in New Jersey, New York, and Delaware to evaluate cucumber (‘Python’), eggplant (‘Santana’), and snap bean (‘Caprice’ and ‘Huntington’) injury and yield response to simulated dicamba drift rates. Crops were exposed to dicamba applied at 0, 0.056, 0.11, 0.56, 1.12, 2.24 g ae ha–1, representing 0, 1/10,000, 1/5,000, 1/1,000, 1/500, and 1/250 of the maximum soybean recommended label rate (560 g ae ha–1), respectively. Dicamba was applied either at the early vegetative (V2) or early reproductive (R1) stages. Minimal to no injury, vine growth reduction, or yield loss was noted for cucumber. Dicamba was more injurious to eggplant with up to 22% to 35% injury 2 wk after treatment (WAT) at rate ≥1.12 g ae ha–1; however, only the highest dicamba rate caused 27% reduction of the commercial yield compared to the nontreated control. Eggplant also showed greater sensitivity when dicamba exposure occurred at the R1 than at theV2 stage. Snap bean was the most sensitive crop investigated in this study. Injury 2 WAT was greater for ‘Caprice’ with dicamba ≥0.56 g ae ha–1 applied at V2 compared to R1 stage, whereas a similar difference occurred as low as 0.056 g ae ha–1 for ‘Huntington’. Compared to the nontreated control, reduction in plant height and biomass accumulation occurred for both cultivars at dicamba rate ≥0.56 g ae ha–1. Dicamba applied at 1.12 g ae ha–1 or greater resulted in 30% yield loss for ‘Caprice’, whereas ‘Huntington’ yield dropped 52% to 93% with dicamba ≥0.56 g ae ha–1. ‘Caprice’ bean yield was not influenced by dicamba timing of application. Conversely, ‘Huntington’ bean yield decreased by 8% following application at R1 compared to V2 stage.

The role of weed suppression by the cultivated crop is often overlooked in annual row cropping systems. Agronomic practices such as planting time, row spacing, tillage and herbicide selection may influence the time of crop canopy closure. The objective of this research was to evaluate the influence of the aforementioned agronomic practices and their interaction with the adoption of an effective preemergence (PRE) soil residual herbicide program on soybean canopy closure and yield. A field experiment was conducted in 2019 and 2020 in Arlington, WI, as a 2×2×2×2 factorial in a randomized complete block design, including early (late April) and standard (late May) planting time, narrow (38 cm) and wide (76 cm) row spacing, conventional tillage and no-till, and soil-applied PRE herbicide (yes and no; flumioxazin 150 g ai ha−1 + metribuzin 449 g ai ha−1 + pyroxasulfone 190 g ai ha−1). All plots were maintained weed-free throughout the growing season. In both years, early planted soybeans reached 90% green canopy cover (T90) before (7 to 9 d difference) and yielded more (188 to 902 kg ha−1 difference) than the standard planted soybeans. Narrow-row soybeans reached T90 earlier than wide-row soybeans (4 to 7 d difference), but yield was similar between row spacing treatments. Conventional tillage resulted in a higher yield compared to a no-till system (377 kg ha−1 difference). The PRE herbicide slightly delayed T90 (4 d or less) but had no impact on yield. All practices investigated herein influenced the time of soybean canopy closure but only planting time and tillage impacted yield. Planting soybeans earlier and reducing their row spacing expedites the time to canopy closure. The potential delay in canopy development and yield loss if soybeans are allowed to compete with weeds early in the season would likely outweigh the slight delay in canopy development by an effective PRE herbicide.

Field trials were conducted to determine the effects of glyphosate and/or dicamba simulated drift rates on chipping potatoes (Solanum tuberosum L.) ‘Atlantic’ and ‘Dakota Pearl.’ Sublethal herbicide rates were applied at the tuber initiation stage and consisted of dicamba at 99 g ae ha−1 or glyphosate at 197 g ae ha−1 applied alone or the combinations of dicamba at 20 or 99 g ae ha−1 and glyphosate at 40 or 197 g ae ha−1, respectively. At 7 days after treatment (DAT), the high spray combination of glyphosate plus dicamba resulted in the greatest plant damage (28%). Plant injury from plants treated with the low combination of glyphosate plus dicamba did not differ from the nontreated control. At 21 DAT, visible injury increased to 40% for plants treated with the high combination of glyphosate plus dicamba. Total yield suggested that dicamba and glyphosate caused similar yield reductions as plants that received glyphosate at 197 g ha−1 or dicamba at 99 g ha−1 had lower total yields compared to the nontreated and plants that received the combination of glyphosate (197 g ha−1) and dicamba (99 g ha−1) had lower total yields compared to plants that received either herbicide alone. However, ‘Dakota Pearl’ plants were more sensitive to glyphosate at 197 g ha−1 than were ‘Atlantic’ plants, causing the interaction for most tuber grades. Tuber specific gravity was lower for plants that received glyphosate at 197 g ha−1, dicamba at 99 g ha−1, or this combination, but this reduction would not prevent chip processing. Results reinforce the need for diligence when applying these herbicides in proximity to a susceptible crop, such as chipping potatoes, and the need to thoroughly clean sprayers before application to a sensitive crop.

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.

Rhizoma perennial peanut (RPP) is well adapted to the Gulf Coast region of the United States, but its varietal tolerance to glyphosate and triclopyr is not well defined. The research was conducted to determine the effect of various rates of glyphosate and triclopyr on established RPP, and the response of common RPP varieties to these herbicides. The RPP sward was approximately 7 yr younger at Zolfo Springs than at the Ona location. RPP showed moderate tolerance to glyphosate and triclopyr application, and injury level did not differ with the age of RPP sward. However, biomass production was negatively influenced by the age of the RPP sward. Overall, injury from glyphosate applications did not exceed 40% at either site. The glyphosate rate for 20% biomass reduction was predicted to be 0.53 and 2.17 kg ae ha−1 at Zolfo Springs and Ona, respectively. RPP injury from triclopyr was greater at the Zolfo Springs location than at Ona, and the triclopyr rate predicted to result in a 20% biomass reduction was 0.45 and 0.99 kg ae ha−1 at the Zolfo Springs and Ona locations, respectively. There was a difference on RPP varieties response to glyphosate and triclopyr application. ‘Florigraze’ and ‘Ona 33’ were less tolerant to glyphosate compared to ‘UF-Tito’ and ‘Ecoturf’ at 30 d after treatment. Likewise, UF-Tito and Florigraze were less tolerant to triclopyr compared to Ona 33 and Ecoturf. Overall, Florigraze showed highest injury and at least 2-fold reduction on biomass compared to the other three varieties from glyphosate or triclopyr application. Results from this research indicate that glyphosate and triclopyr appear to be safe to apply to long-established RPP stands, but herbicide rate and RPP varieties should be considered if stands are <5 yr old.

The use of photosystem II (PSII)-inhibitor and/or protoporphyrinogen oxidase (PPO)-inhibitor PRE herbicides in soybean may, under adverse environmental conditions, result in early season crop injury. A field study was conducted near Brule and North Platte, Nebraska, during the 2016 and 2017 growing seasons with the objective to evaluate the impact of PRE herbicides metribuzin (PSII-inhibitor) and sulfentrazone (PPO-inhibitor) on early season soybean development, final plant stand, and yield using 22 soybean varieties adapted to southwestern Nebraska. Herbicide treatments consisted of metribuzin (560 g ai ha−1) and sulfentrazone (280 g ai ha−1) applied within 3 d after planting and a nontreated control (NTC). Sulfentrazone reduced green canopy vegetation at the V2 growth stage by 22% and final plant stand at physiological maturity by 10% compared with the NTC. The number of pods per plant was 16% higher for sulfentrazone and the number of seeds per plant was 15% and 4% higher for sulfentrazone and metribuzin compared with the NTC, respectively. Sulfentrazone and metribuzin resulted in a slightly higher yield (3%) compared with the NTC, thus no yield reduction from PRE herbicides was observed in this study. These results support other findings that sulfentrazone and metribuzin have potential to cause early-season crop injury; however, when applied according to their label recommendations and following regional agronomic management practices, this impact may not translate into soybean yield reduction while such herbicides provide effective soil residual weed control.

Many factors such as environment, herbicide rate, growth stage at application, and days between sequential applications can influence the response of a crop to herbicides. Florpyrauxifen-benzyl is a new broad-spectrum, POST herbicide that was commercialized for use in U.S. rice production in 2018. Field experiments were conducted in 2018 at the Pine Tree Research Station (PTRS) near Colt, AR, and the Rice Research and Extension Center (RREC), near Stuttgart, AR, to evaluate crop injury and yield response of three rice cultivars to sequential applications of florpyrauxifen-benzyl. Greenhouse and growth chamber experiments were conducted at the Altheimer Laboratory in Fayetteville, AR, to evaluate cultivar responses when florpyrauxifen-benzyl was applied at 30 or 60 g ae ha−1 to rice exposed to different temperature regimes or at various growth stages. Three rice cultivars were used in all experiments: long-grain variety ‘CL111’, medium-grain variety ‘CL272’, and long-grain hybrid cultivar ‘CLXL745’. CL111 exhibited sufficient tolerance to florpyrauxifen-benzyl with only 10% visible injury and no effect on yield. CL272 showed 15% injury 3 wk after the second application in the field experiment when applications were made 14 d apart. Additionally, 12% injury was observed in greenhouse studies when florpyrauxifen-benzyl was applied at 30 g ae ha−1, averaged over various growth stages at application. Florpyrauxifen-benzyl did not reduce the yield of CL272 in field experiments, indicating that CL272 can recover from florpyrauxifen-benzyl injury. As much as 64% injury was observed for CLXL745 at 3 wk after application (WAA) when sequential herbicide applications were made 4 d apart. High levels of injury occurred in the growth chamber and greenhouse studies for this cultivar as well. Sequential applications of florpyrauxifen-benzyl reduced yields of CLXL745 in nearly all treatments. Data from these experiments suggest that CL272 and CLXL745 are sensitive to sequential applications of florpyrauxifen-benzyl. Growers must follow the prescribed guidelines for using florpyrauxifen-benzyl in these cultivars and others like it.

Field studies were conducted in 2017 and 2018 in Arkansas to evaluate the injury caused by herbicides on soybean canopy formation and yield. Fomesafen, acifluorfen, S-metolachlor + fomesafen, and S-metolachlor + fomesafen + chlorimuron alone and in combination with glufosinate were applied to glufosinate-resistant soybean at the V2 growth stage. Soybean injury resulting from these labeled herbicide treatments ranged from 9% to 25% at 2 wk after application. This level of injury resulted in a 4-, 5-, 6-, and 6-d delay in soybean reaching 80% groundcover following fomesafen, acifluorfen, S-metolachlor + fomesafen, and S-metolachlor + fomesafen + chlorimuron, respectively. There was a 2-d delay in soybean reaching a canopy volume of 15,000 cm3 following each of the four herbicide treatments. The addition of glufosinate to the herbicide applications resulted in longer delays in canopy formation with every herbicide treatment except glufosinate + fomesafen. Fomesafen, acifluorfen, S-metolachlor + fomesafen, and S-metolachlor + fomesafen + chlorimuron, each applied with glufosinate, delayed soybean from reaching 80% groundcover by 2, 7, 8, and 9 d, respectively, and delayed the number of days for soybean to reach a canopy volume of 15,000 cm3 by 2, 3, 2, and 2 d, respectively. No yield loss occurred with any herbicide application. A delay in percent groundcover in soybean allows sunlight to reach the soil surface for longer periods throughout the growing season, possibly promoting late-season weed germination and the need for an additional POST herbicide application.

An experiment was conducted in 2017 and 2018 to determine the sensitivity of driftable rates of 2,4-D and dicamba with or without glyphosate on common ornamental, fruit, and nut species. Three driftable rates corresponding to ½, 1/20th, and 1/200th of the manufacturer’s labeled rate (1 × rate) of 2,4-D (1.09 kg ae ha−1), 2,4-D plus glyphosate (1.09 kg ae ha−1 plus 1.10 kg ae ha−1), dicamba (0.56 kg ae ha−1), and dicamba plus glyphosate (0.56 kg ae ha−1 plus 1.10 kg ae ha−1) were applied to apple, crabapple, dogwood, American elderberry, American elm, grapevine, hydrangea, red maple, pin oak, peach, pecan, eastern redbud, rose, red raspberry, strawberry, sweetgum, nannyberry viburnum, and black walnut plants. Visible estimates of injury were recorded 28 and 56 days after treatment (DAT). Plant measurements included leaf malformation, tree trunk growth, and shoot length. Across all species, the ½ × rate of 2,4-D plus glyphosate resulted in 61% injury 28 DAT, whereas the ½ × rate of dicamba plus glyphosate resulted in 51% injury. Across plant species and herbicides, ½ ×, 1/20 ×, and 1/200 × rates caused injury ranging from 3% to 100%, 0% to 66%, and 0% to 19%, respectively. Hydrangea was the least sensitive species; grapevine was most sensitive. Changes in plant measurements were dependent on the species and herbicide applied. Treatments at the ½ × or 1/20 × rate resulted in shoot length, leaf malformation, and trunk tree diameter differences for 11, 10, and 7 species, respectively, compared with nontreated plants. Collectively, the measurements and visual injury assessments indicated apple, red maple, peach, and pin oak were more sensitive to treatments containing dicamba, whereas black walnut, grapevine, and American elm were more sensitive to 2,4-D. Although the 1/200 × rates of 2,4-D and dicamba did not result in changes to plant measurements, obvious injury symptoms were observed, which could render these plants unsalable.

The objective for this study was to determine if POST-directed applications of flumioxazin reduce fruit yield for chile pepper produced on coarse- and fine-textured soils irrigated by furrow. This objective was addressed with a multiyear (2015, 2016, 2017) field study that compared flumioxazin effects on fruit yield against a commercial standard (POST-directed carfentrazone) and the absence of a POST-directed herbicide. The field study occurred at two university research farms that differed in soil texture. On fine-textured soil, treatments included the no POST–directed herbicide control and the following four POST-directed herbicides applied to raised beds: (1) flumioxazin at 107 g ai ha–1 applied 4 wk after crop thinning, (2) carfentrazone at 35 g ai ha–1 applied 4 wk after crop thinning, (3) flumioxazin at 70 g ai ha–1 applied 4 and 6 wk after crop thinning, (4) carfentrazone at 35 g ai ha–1 applied 4 and 6 wk after crop thinning. On coarse-textured soil, treatments included the no POST–directed herbicide control and the following three POST-directed herbicides applied 4 wk after crop thinning: (1) flumioxazin at 107 g ai ha–1 applied to raised beds, (2) flumioxazin at 107 g ai ha–1 applied to furrows, (3) carfentrazone at 35 g ai ha–1 applied to raised beds. On fine-textured soil, treatment did not affect fruit yield. On coarse-textured soil, flumioxazin applied to furrows did not reduce fruit yield, but flumioxazin on raised beds reduced fruit yield of some cultivars in 2015 and 2017. Year-to-year variability in both flumioxazin-induced yield loss and soil characteristics suggested that chile pepper sensitivity to flumioxazin was negatively associated with soil organic matter content. In a follow-up greenhouse study, soil organic matter lessened flumioxazin-induced crop injury. In general, this study indicates that recommendations for POST-directed flumioxazin in New Mexico chile pepper will need to be soil-type specific.

The commercial release of crops with engineered resistance to 2,4-D and dicamba will alter the spatial and temporal use of these herbicides. This, in turn, has elicited concerns about off-target injury to sensitive crops. In 2014 and 2015, studies were conducted in Tifton, GA, to describe how herbicide (2,4-D and dicamba), herbicide rate (1/75 and 1/250 field use), and application timing (20, 40, and 60 DAP) influence watermelon injury, vine development, yield, and the accumulation of herbicide residues in marketable fruit. In general, greater visual injury and reductions in vine growth, relative to the non-treated check, were observed when herbicide applications were made before watermelon plants had begun to flower. Although the main effects of herbicide and rate were less influential than the timing of applications with respect to plant development, the 1/75 rates were more injurious than the 1/250 rates; dicamba was more injurious than 2,4-D. In 2014, the 1/75 and 1/250 rates of each herbicide reduced marketable fruit numbers 13 to 20%, but only for the 20 DAP application. The 1/75 rate of each herbicide when applied at either 20 or 40 DAP reduced the number of fruit harvested per plot in 2015. Dicamba residues were detected in marketable fruit when the 1/75 rate in 2014 and 2015 and the 1/250 rate in 2015 was applied to plants at 40 or 60 DAP. Residues of 2,4-D were detected in 2015 when the 1/75 and 1/250 rates were applied at 60 DAP. Across both years, the maximum level of residue detected was 0.030 ppm. While early season injury may reduce watermelon yields, herbicide residue detection is more likely in marketable fruit when an off-target contact incident occurs closer to harvest.

Control of noxious weeds such as cogongrass depend heavily on chemical treatment, but success is limited unless integrated with other practices. Utilization of cover crops in the system is ideal to avoid the use of excess herbicide and replace vegetation that will resist cogongrass reinvasion. Greenhouse studies were conducted from 2013 through 2015 at Mississippi State University with the objective to evaluate ‘AG4934’ RR/STS soybean, Korean lespedeza, crimson clover and ‘Durana’ white clover tolerance to soil-applied imazapyr at selected rates and various planting times after application. Plastic containers filled with a mixture of 2:1 sand:topsoil were treated with imazapyr at 0, 70, 140 and 280 g ae ha–1. Legume species were planted 0, 1, 3 and 6 months after treatment (MAT). The factorial experimental design included legume species, imazapyr rate and planting time. At 6 weeks after each planting, the number of seedlings, average plant height and shoot biomass were measured. Statistical analysis revealed the imazapyr rate x planting time interaction was significant with respect to number of emerged seedlings, average height and shoot biomass per plant for each species. It was observed that the legumes planted at 0 MAT of imazapyr at 70 g ae ha–1 or higher reduced emerged seedlings, average height and biomass production. In general, seeds planted 1 MAT or later in combination with these same herbicide rates, showed less growth reductions than treatments seeded 0 MAT. In conclusion, sites treated with imazapyr rates from 70 to 280 g ae ha–1 for weed control, should not be seeded with legume ground covers less than 1 month after treatment to reduce emergence failure, plant height and biomass production.