Italian ryegrass control is one of the most significant limitations in wheat production in the United States today. Resistance to Herbicide Resistance Action Committee (HRAC)/Weed Science Society of America (WSSA) Groups 1, 2, and 9 in Arkansas have further complicated postemergence control, whereas residual herbicides still show effective weed control. One problem is the potential of HRAC/WSSA Group 15 herbicides to injure wheat when applied preemergence, indicating the need for a herbicide safener. A series of experiments were conducted in Fayetteville, AR, to evaluate crop tolerance and Italian ryegrass control using a capsule suspension (CS) formulation of S-metolachlor in conjunction with fenclorim-treated wheat. Experiments were conducted as a two-factor factorial with S-metolachlor applied at three rates (0.37, 0.74, and 1.12 kg ai ha–¹) and a microencapsulated formulation of acetochlor at 1.05 kg ai ha–¹, and three rates of a fenclorim seed treatment at 0, 0.5, and 2.0 g ai kg^–1 of seed. Separate experiments utilized either a preemergence (PRE) or a delayed-preemergence (DPRE) application timing. In both experiments, S-metolachlor at 0.74 and 1.12 kg ai ha–¹ provided 77% to 96% control of Italian ryegrass by preharvest, whereas acetochlor only provided 49% to 72% control. Visible wheat injury from PRE applications ranged from 7% to 49% for all treatments 21 d after treatment (DAT), with a reduction in injury when fenclorim-treated wheat was used for both the 0.74 and 1.12 kg ai ha–¹ rate of S-metolachlor. In the DPRE experiments, wheat injury ranged from 5% to 16% 21 DAT with no noticeable safening from the presence of fenclorim at any herbicide rate. The results of these experiments indicate that a DPRE application using a CS formulation of S-metolachlor would be more favorable for producers to mitigate the potential for injury to wheat while providing Italian ryegrass control. Additionally, at the DPRE application timing, fenclorim is unnecessary for S-metolachlor to be safely applied at the rates evaluated.

Nomenclature: Acetochlor; S-metolachlor; Italian ryegrass, Lolium perenne L. ssp. multiflorum (Lam.) Husnot; wheat, Triticum aestivum L.

Novel management strategies for controlling smutgrass have potential to influence sward dynamics in bahiagrass forage systems. This experiment evaluated population shifts in bahiagrass forage following implementation of integrated herbicide and fertilizer management plans for controlling smutgrass. Herbicide treatments included indaziflam applied PRE, hexazinone applied POST, a combination of PRE + POST herbicides, and a nonsprayed control. Fertilizer treatments included nitrogen, nitrogen + potassium, and an unfertilized control. The POST treatment reduced smutgrass coverage regardless of PRE or fertilizer application by the end of the first season and remained low for the 3-yr duration of the experiment (P < 0.01). All treatments, including nontreated controls, reduced smutgrass coverage during year 3 (P < 0.05), indicating that routine harvesting to remove the biomass reduced smutgrass coverage. Bahiagrass cover increased at the end of year 1 with POST treatment (P < 0.01), but only the POST + fertilizer treatment maintained greater bahiagrass coverage than the nontreated control by the end of year 3 (P < 0.05). Expenses associated with the POST + fertilizer treatment totaled US$348 ha–¹ across the 3-yr experiment. Other smutgrass control options could include complete removal of biomass (hay production) and pasture renovation, which can cost 3-fold or greater more than POST + fertilizer treatment. Complete removal of biomass may reduce smutgrass coverage by removing mature seedheads, but at a much greater expense of US$2,835 to US$5,825 ha–¹, depending on herbicide and fertilizer inputs. Bahiagrass renovation is US$826 ha–¹ in establishment costs alone. When pasture production expenses are included for two seasons postrenovation, the total increases to US$1,120 ha–¹ across three seasons. The importance of hexazinone and fertilizer as components of smutgrass control in bahiagrass forage was confirmed in this study. Future research should focus on the biology of smutgrass and the role of a PRE treatment in a long-term, larger-scale forage system.

Nomenclature: Hexazinone; indaziflam; bahiagrass, Paspalum notatum Fluggé; smutgrass, Sporobolus indicus (L.) R. Br.

An experiment was conducted in 2022 and 2023 near Rocky Mount and Clayton, NC, to evaluate residual herbicide-coated fertilizer for cotton tolerance and Palmer amaranth control. Treatments included acetochlor, atrazine, dimethenamid-P, diuron, flumioxazin, fluometuron, fluridone, fomesafen, linuron, metribuzin, pendimethalin, pyroxasulfone, pyroxasulfone + carfentrazone, S-metolachlor, and sulfentrazone. Each herbicide was individually coated on granular ammonium sulfate (AMS) and top-dressed at 321 kg ha–¹ (67 kg N ha–¹) onto 5- to 7-leaf cotton. The check plots received the equivalent rate of nonherbicide-treated AMS. Before top-dress, all plots (including the check) were treated with glyphosate and glufosinate to control previously emerged weeds. All herbicides except metribuzin resulted in transient cotton injury. Cotton response to metribuzin varied by year and location. In 2022, metribuzin caused 11% to 39% and 8% to 17% injury at the Clayton and Rocky Mount locations, respectively. In 2023, metribuzin caused 13% to 32% injury at Clayton and 73% to 84% injury at Rocky Mount. Pyroxasulfone (91%), pyroxasulfone + carfentrazone (89%), fomesafen (87%), fluridone (86%), flumioxazin (86%), and atrazine (85%) controlled Palmer amaranth ≥85%. Pendimethalin and fluometuron were the least effective treatments, resulting in 58% and 62% control, respectively. As anticipated, early season metribuzin injury translated into yield loss; plots treated with metribuzin yielded 640 kg ha–¹ and were comparable to yields after linuron (790 kg ha–¹) was used. These findings suggest that with the exception of metribuzin, residual herbicides coated onto AMS may be suitable and effective in cotton production, providing growers with additional modes of action for late-season control of multiple herbicide–resistant Palmer amaranth.

Nomenclature: Acetochlor; atrazine; dimethenamid-P; diuron; flumioxazin; fluometuron; fluridone; fomesafen; glufosinate; glyphosate; linuron; metribuzin; pendimethalin; pyroxasulfone; pyroxasulfone + carfentrazone; S-metolachlor; sulfentrazone; Palmer amaranth, Amaranthus palmeri S. Watson. AMAPA; cotton, Gossypium hirsutum L.

In 2022, trials were carried out in New Jersey and New York to assess the efficacy of weed management and the response of two cole crops to various herbicide combinations and rates. The experiments involved the application of S-metolachlor and microencapsulated (ME) acetochlor either alone or combined with oxyfluorfen. Different application timings of oxyfluorfen were tested in greenhouse and field studies. Results from the greenhouse trials show that substituting S–metolachlor with ME acetochlor in over-the-top applied mixes with oxyfluorfen caused 15% to 22% less crop injury and increased seedling biomass by 33%. In field studies, nontreated plots exhibited significant weed growth, reaching up to 71% coverage 28 d after transplanting (DATr), whereas herbicide-treated plots exhibited weed cover at or below 10% by 28 DATr. Mixtures or sequential applications of oxyfluorfen and chloroacetamides achieved excellent control (≥99%) of the weed species complex compared to single applications of oxyfluorfen or chloroacetamides. However, applying both oxyfluorfen and a chloroacetamide posttransplanting, either as a tank mixture or in sequence, resulted in ≥19% injury. Despite the effective weed control achieved with herbicide treatments, mixing herbicides posttransplanting reduced relative commercial yield by 46% to 94% compared to oxyfluorfen applied alone or followed by chloroacetamides. The findings from these experiments will inform regional crop safety guidelines and support potential modifications to oxyfluorfen labels regarding sequential applications with chloroacetamides.

Nomenclature: Acetochlor; oxyfluorfen; S-metolachlor; chloroacetamides

Common cattail is a perennial weed that naturally occurs in wet or saturated soils, such as in marshes, lakes, ponds, irrigation and drainage canals, and streams, throughout North America. Recently, common cattail has become an important problem for the drill-seeded rice systems in the Sacramento–San Joaquin River Delta of northern California. This research was conducted in 2022 and 2023 at three sites near Stockton, CA, to evaluate the efficacy of florpyrauxifen-benzyl, a newly registered auxin-mimic herbicide, to control common cattail in drill-seeded rice. Florpyrauxifen-benzyl was applied alone at 40 g ai ha–¹ and 80 g ha–¹ on 0- to 1-m-tall and 1- to 2-m-tall common cattail and in a sequential application of florpyrauxifen-benzyl at 40 g ha–¹ followed by 40 g ha–¹ between 14-d intervals on 0- to 1-m-tall and 1- to 2-m-tall common cattail. Triclopyr, another auxin-mimic rice herbicide widely used in California, was applied alone at 420 g ae ha–¹ on 0- to 1-m-tall common cattail for comparison. Triclopyr was also applied in combination with florpyrauxifen-benzyl at 40 g ha–¹ at the 0- to 1-m growth stage. The injury symptoms on common cattail started within 3 d after treatment (DAT) for the florpyrauxifen-benzyl + triclopyr mixture treatment and within 7 DAT for all other florpyrauxifen-benzyl applied treatments. All florpyrauxifen-benzyl treatments controlled 100% of common cattail at 28 DAT regardless of application rate and timing. Common cattail height and dry biomass at 28 DAT were lower for all treatments compared to the nontreated control. While the common cattail control was excellent for all florpyrauxifen-benzyl applications, rice injury was minimal. This research indicates that common cattail up to 2 m tall can be effectively and rapidly controlled in rice fields with florpyrauxifen-benzyl at 40 g ha–¹.

Nomenclature: Florpyrauxifen-benzyl; triclopyr; common cattail, Typha latifolia L. ‘TYLA’; rice, Oryza sativa L.

This study assessed the potential of using dichlobenil to manage hair fescue in lowbush blueberry crops when targeted or broadcast-applied (7,000 g ai ha^–1) as justification for developing a precision-targeted applicator. A randomized complete block design was used to assess both application methods, and results were compared with industry-standard propanamide (2,240 g ai ha^–1). Targeted and broadcast-applied dichlobenil in fall 2020 significantly reduced average total tuft density in the nonbearing year (2021) by 75% and 67%, respectively, and in the bearing year (2022) by 61% and 59%, respectively. Broadcast pronamide applications in fall 2020 significantly reduced total tuft density by 84% in the nonbearing year (2021) and 81% in the bearing year (2022). These reductions in total tuft density resulted in average lowbush blueberry yields of 416, 557, 573, and 617 g m^–2 for the control, pronamide applications, and targeted and broadcast-applied dichlobenil, respectively. Increases in yield were not significant, though the large variation within the sample is the probable cause. The similarities between targeted and broadcast-applied treatments demonstrate the potential of using targeted dichlobenil. Given the high product cost of dichlobenil at Can$1,873 ha^–1, hair fescue's non-uniform distribution in lowbush blueberry fields and the lowbush blueberry industry's overreliance on pronamide, targeted application of dichlobenil has significant potential. This work justifies the development of a mechanized precision-targeted applicator for use in lowbush blueberry cropping systems.

Nomenclature: Dichlobenil; pronamide; hair fescue, Festuca filiformis; lowbush blueberry, Vaccinium angustifolium Ait.

Two studies were conducted in 2022 and 2023 near Rocky Mount and Clayton, NC, to determine the optimal granular ammonium sulfate (AMS) rate and application timing for pyroxasulfone-coated AMS. In the rate study, AMS rates included 161, 214, 267, 321, 374, 428, and 481 kg ha–¹, equivalent to 34, 45, 56, 67, 79, 90, and 101 kg N ha–¹, respectively. All rates were coated with pyroxasulfone at 118 g ai ha–¹ and topdressed onto 5- to 7-leaf cotton. In the timing study, pyroxasulfone (118 g ai ha–¹) was coated on AMS and topdressed at 321 kg ha–1 (67 kg N ha–¹) onto 5- to 7-leaf, 9- to 11-leaf, and first bloom cotton. In both studies, weed control and cotton tolerance to pyroxasulfone-coated AMS were compared to pyroxasulfone applied POST and POST-directed. The check in both studies received non-herbicide-treated AMS (321 kg ha–¹). Before treatment applications, all plots (including the check) were maintained weed-free with glyphosate and glufosinate. In both studies, pyroxasulfone applied POST was most injurious (8% to 16%), while pyroxasulfone-coated AMS resulted in ≤4% injury. Additionally, no differences in cotton lint yield were observed in either study. With the exception of the lowest rate of AMS (161 kg ha–¹; 79%), all AMS rates coated with pyroxasulfone controlled Palmer amaranth ≥83%, comparably to pyroxasulfone applied POST (92%) and POST-directed (89%). In the timing study, the application method did not affect Palmer amaranth control; however, applications made at the mid- and late timings outperformed early applications. These results indicate that pyroxasulfone-coated AMS can control Palmer amaranth comparably to pyroxasulfone applied POST and POST-directed, with minimal risk of cotton injury. However, the application timing could warrant additional treatment to achieve adequate late-season weed control.

Nomenclature: Pyroxasulfone; Palmer amaranth; Amaranthus palmeri S. Watson; cotton, Gossypium hirsutum L.

With Palmer amaranth and waterhemp evolving resistance to nine and six different sites of action (SOAs) globally, soybean producers continue to search for new options to control these problematic weeds. Bayer CropScience has announced its intentions to launch a Convintro™ brand of herbicides, one being a three-way premixture for preemergence use in soybean. The premixture will contain diflufenican (WSSA Group 12), metribuzin (WSSA Group 5), and flufenacet (WSSA Group 15), adding a new SOA for soybean producers throughout the United States. With the anticipated launch of the premixture, research is needed to evaluate the length of residual control provided by the new herbicide. Research trials were conducted in Fayetteville and Keiser, AR, and Morrice, MI, in 2022 and 2023. A 0.17:0.35:0.48 ratio of a diflufenican: metribuzin:flufenacet (DFF)-containing premixture was applied alone and in combination with additional metribuzin and dicamba. Also, metribuzin, acetochlor, a S-metolachlor:metribuzin premixture, and a flumioxazin:pyroxasulfone:metribuzin premixture were applied preemergence. The DFF-containing premixture was more effective in reducing Palmer amaranth/waterhemp emergence than acetochlor in four of six trials at 28 d after treatment (DAT). Palmer amaranth and waterhemp densities in plots treated with the DFF-containing premixture exhibited similar results to plots treated with the S-metolachlor:metribuzin premixture and the flumioxazin:pyroxasulfone:metribuzin premixture at 28 DAT. By 56 DAT, Palmer amaranth and waterhemp densities were comparable or superior in plots with the DFF-containing premixture than in those treated with acetochlor and metribuzin, and the S-metolachlor: metribuzin premixture at five of six sites. The addition of dicamba or metribuzin to the DFF-containing premixture did not reduce Palmer amaranth or waterhemp density compared to the DFF-containing premixture at 28 or 56 DAT. Overall, the DFF-containing premixture generally provided greater or comparable control over several standard herbicides, providing growers a new product for preemergence control of Amaranthus species in soybean fields.

Nomenclature: Acetochlor; dicamba; diflufenican; flufenacet; flumioxazin; metribuzin; pyroxasulfone; Palmer amaranth, Amaranthus palmeri (S.) Wats.; waterhemp, Amaranthus tuberculatus; soybean, Glycine max (L.) Merr.

The opportunity to increase soybean yield has prompted Illinois farmers to plant soybean earlier than historical norms. Extending the growing season with an earlier planting date might alter the relationship between soybean growth and weed emergence timings, potentially altering the optimal herbicide application timings to minimize crop yield loss due to weed interference and ensure minimal weed seed production. The objective of this research was to examine various herbicide treatments applied at different timings and rates to assess the effect on weed control and yield in early-planted soybean. Field experiments were conducted in 2021 at three locations across central Illinois to determine effective chemical strategies for weed management in early-planted soybean. PRE treatments consisted of a S-metolachlor + metribuzin premix applied at planting or just prior to soybean emergence at 0.5X (883 + 210 g ai ha–¹) or 1X (1,766 + 420 g ai ha–¹) label-recommended rates. POST treatments were applied when weeds reached 10 cm tall and consisted of 1X rates of glufosinate (655 g ai ha–¹) + glyphosate (1,260 g ae ha–¹) + ammonium sulfate, without or with pyroxasulfone at a 0.5X (63 g ai ha–¹) or 1X (126 g ai ha–¹) rate. Treatments comprising both a full rate of PRE followed by a POST resulted in the greatest and most consistent weed control at the final evaluation timing. The addition of pyroxasulfone to POST treatments did not consistently reduce late-season weed emergence. The lack of a consistent effect by pyroxasulfone could be attributed to suppression of weeds by soybean canopy closure due to earlier soybean development. The full rate of PRE extended the timing of POST application 2 to 3 wk for all treatments at all locations except Urbana. Full-rate PRE treatments also reduced the time between the POST application and soybean canopy closure. Overall, a full-rate PRE reduced early-season weed interference and minimized soybean yield loss due to weed interference.

Nomenclature: Glufosinate; glyphosate; metribuzin; pyroxasulfone; S-metolachlor; soybean, Glycine max (L.) Merr.

Alternative strategies to fumigation are needed to manage weeds and improve strawberry fruit yield in annual hill plasticulture production systems. Field experiments were conducted in Blackstone, VA, for two consecutive growing seasons, 2013/14 and 2014/15, to assess the efficacy of 4 wk and 8 wk soil solarization (SS) and application of mustard seed meal (MSM) at 1,121 kg ha–¹, alone and in combination, for weed control efficacy and crop yield estimation in this production system. These treatments were compared to the use of 1,3-dichloropropene (1,3-D) chloropicrin (Pic) as a fumigation standard at 188 kg ha–¹ and an untreated control (UTC). Over both growing seasons, compared to 1,3-D Pic, the SS-MSM-8wk and SS-8wk treatments provided equivalent or reduced cumulative weed count, including weed count of several dominant weed species such as annual ryegrass, speedwell, common chickweed, and cudweed. The SS-4wk and MSM-4wk treatments did not affect weed density compared with the UTC. The MSM-8 wk and 4-wk treatments reduced cumulative weed counts over that of the UTC. In the second growing season, the total yield was significantly higher after the 1,3-D Pic fumigation treatment compared with yield after other treatments. The SS-4wk, MSM-4wk, and MSM-8wk treatments did not improve the total or marketable yield compared with the UTC. The marketable yield after the SS-MSM-8wk treatment was similar to that of the 1,3-D Pic treatment. In conclusion, the SS-8wk and SS-MSM-8wk treatments may be effective weed management strategies for organic growers, small farms, or growers who cannot use chemical fumigants due to new regulations and potential risks to human health.

Nomenclature:Chloropicrin, 1; 3-dichloropropene; annual ryegrass, Lolium multiflorum L.; speedwell, Veronica filiformis S.; common chickweed, Stellaria media L.; cudweed, Gnaphalium L.; strawberry, Fragaria xananassa Duchesne

Field studies were conducted on certified organic land in Lafayette and Vincennes, IN, in 2023 to determine the impact of different between-row weed control methods on weed suppression and sweetpotato yield. Between-row treatments consisted of organic buckwheat (108 kg ha^–1) broadcast seeded immediately after sweetpotato transplanting followed by silage tarping from 3 wk after transplanting (WATr) through harvest, organic buckwheat (108 kg ha^–1) broadcast seeded 3 WATr and terminated 7 WATr, and cultivation as a grower standard. Weed density at 6 WATr was 0, 184, and 162 plants m^–2 for the silage tarping, living mulch buckwheat, and cultivation treatments, respectively. Total yield was 11,048 kg ha^–1 for the living mulch buckwheat, 19,792 kg ha^–1 for the cultivation, and 17,814 kg ha^–1 for the tarping treatments. Tarping effectively suppressed weeds and produced sweetpotato yields comparable to cultivation, indicating the potential for use by organic growers. When buckwheat was grown between rows 3 to 7 WATr, sweetpotato yield was lower than it was with tarping and cultivation. These results suggest that researchers should be evaluating tarps for small-acreage farmers as a weed management strategy.

Nomenclature: Buckwheat, Fagopyrum esculentum Moench; sweetpotato, Ipomoea batatas (L.) Lam. ‘Covington'

As herbicide resistance continues to render commonly used rice herbicides ineffective, alternative sites of action are paramount to maintaining yield and producer profitability. Combining a slow-release formulation and a fenclorim seed treatment might allow the safe use of S-metolachlor in rice. Experiments were initiated in 2022 and 2023 near Colt, AR, on a silt loam soil to evaluate crop safety using a capsule suspension (CS) formulation of S-metolachlor and a fenclorim seed treatment in rice. The first experiment assessed the tolerance of two cultivars (‘Diamond’ and ‘DG263L’) to three rates (0.42, 0.84, and 1.68 kg ai ha–¹) of a CS S-metolachlor at a delayed preemergence (DPRE) application timing in conjunction with a fenclorim seed treatment. The second experiment evaluated a 1- to 2-leaf (EPOST) application of a CS S-metolachlor at 0.56 and 1.12 kg ai ha–¹ to fenclorim-treated rice. Fenclorim reduced injury and partially protected rice yield when S-metolachlor was applied DPRE at 1.68 kg ai ha–1 in both years. However, in one year, under adverse conditions, rice yields were only 65% and 66% of the nontreated control for fenclorim-treated ‘Diamond’ and ‘DG263L’, respectively. An EPOST application of S-metolachlor at 1.12 kg ai ha–¹ resulted in 44% to 51% visible injury 35 d after treatment. Relative rice yields were 88% and 89% of the nontreated weed-free treatment in 2022 and 2023, respectively. Fenclorim provided enhanced crop safety at both the 0.84 and 1.68 kg ai ha–¹ rates of S-metolachlor. However, the potential for reduced yield can arise when unfavorable conditions occur soon after application. An EPOST application timing of CS S-metolachlor at 0.56 kg ai ha–¹ may be a viable option in rice, but 1.12 kg ai ha–¹ is too high on a silt loam soil, resulting in significant rice injury.

Nomenclature:Fenclorim; S-metolachlor; rice, Oryza sativa L.

The widespread adoption of multiple-herbicide-resistant corn and soybean often causes the problem of volunteers in corn–soybean rotation, which necessitates alternative herbicides for effective management. The objective of this research was to evaluate PRE and POST herbicides labeled in corn for control of dicamba/glufosinate/glyphosate-resistant volunteer soybean. Field experiments were conducted from 2021 to 2023 near Clay Center, NE. Two separate field experiments were conducted to evaluate 12 PRE and 14 POST herbicides to control volunteer soybean in Enlist® corn. Soybean resistant to dicamba/glufosinate/glyphosate was planted perpendicular to corn rows to mimic volunteer soybean. Among the PRE herbicides tested, acetochlor/clopyralid/flumetsulam (1,190; 1,050/106/34 g ai ha^–1) and acetochlor/clopyralid/mesotrione (2,304; 1,961/133/210 g ai or ae ha^–1) provided 97% and 99% control of volunteer soybean, respectively, in 2021 and 68% and 89% control, respectively, in 2023 at 42 d after PRE. Among POST herbicides tested, 2,4-D choline (1,064 g ae ha^–1), acetochlor/clopyralid/ mesotrione (2,304; 1,961/133/210 g ai or ae ha^–1), atrazine/bicyclopyrone/mesotrione/S-metolachlor (2,409; 700/42/168/1,499 g ai ha^–1), clopyralid/flumetsulam (192; 146/46 g ai ha^–1), nicosulfuron + atrazine (34 + 1,120 g ai ha^–1), and thiencarbazone-methyl/tembotrione + atrazine (76; 12/63 + 896 g ai ha^–1) provided ≥97% volunteer soybean control, ≥94% density reduction, and ≥97% biomass reduction 28 d after POST herbicide application. Corn yield did not differ from the weed-free control in these treatments. The results of this study suggest that PRE and POST herbicides are available for control of dicamba/glufosinate/glyphosate-resistant volunteer soybean in Enlist® corn and that careful selection of an herbicide is required based on the herbicide-resistant soybean planted in the previous year.

Nomenclature: 2,4-D choline; acetochlor; clopyralid; flumetsulam; mesotrione; atrazine; bicyclopyrone; S-metolachlor; nicosulfuron; thiencarbazone-methyl; tembotrione; corn, Zea mays L.; soybean, Glycine max (L.) Merr.

Herbicide-resistant Palmer amaranth is creating additional challenges for producers who choose to adopt a furrow-irrigated rice production system due to the absence of a sustained flood, enabling extended weed emergence. Fluridone has been shown to effectively control Palmer amaranth in cotton production systems and was recently registered for use in rice. Experiments were initiated in 2022 and 2023 1) to evaluate Palmer amaranth control and rice tolerance to preemergence- and postemergence-applied fluridone at 0.5× (84 g ai ha–¹) and 1× (168 g ai ha–¹) rates on a silt loam soil; and 2) assess the effect of various herbicide programs that contain fluridone on Palmer amaranth biomass, seed production, and rough rice grain yield. Preemergence applications of fluridone at a 1× rate in combination with clomazone resulted in 84% control of Palmer amaranth 21 d after treatment (DAT). Fluridone, in combination with clomazone preemergence, caused up to 36% rice injury 21 DAT; however, early season injury did not negatively affect rice yields. Palmer amaranth biomass and fecundity were reduced with herbicide programs that included fluridone plus florpyrauxifen-benzyl, and, in some instances, there was no Palmer amaranth biomass or seed production following multiple applications of both herbicides. Fluridone- and florpyrauxifen-benzyl–based herbicide programs achieved effective control of Palmer amaranth when applied timely, but injury to hybrid rice is enhanced with preemergence applications of fluridone that are not permitted with the current label.

Nomenclature: Florpyrauxifen-benzyl; fluridone; Palmer amaranth, Amaranthus palmeri (S.) Watson; cotton, Gossypium hirsutum L.; rice, Oryza sativa L.

This trial assessed the effect of preemergence herbicides on newly transplanted blackberries. A 2-yr field trial was initiated in 2021 and conducted at two locations in Fayetteville and Clarksville, AR. Seven treatments consisted of six preemergence herbicides (flumioxazin, mesotrione, napropamide, oryzalin, pendimethalin, and S-metolachlor) and one nontreated check. Preemergence herbicide treatments were applied to field plots of newly transplanted blackberry plugs (‘Ouachita’), using a CO₂ backpack sprayer at 187 L ha–¹ covering a 1-m swath, ensuring spray pattern overlap over newly planted blackberries in 2021 and reapplied in the same manner to established blackberries of the same plots in 2022. Data were collected on crop injury and plant height of blackberry plants in each plot. Yield data were collected in the second year, and fruit were analyzed for soluble solids content, pH, and average berry weight. In the first year, mesotrione and flumioxazin treatments caused injury to newly transplanted blackberries, and mesotrione-treated blackberries (58% in Fayetteville, 29% in Clarksville) did not fully recover by 84 d after treatment (DAT). Napropamide, S-metolachlor, oryzalin, and pendimethalin did not cause crop injury greater than 6% throughout the 2021 season. In the second year (2022), no crop injury was caused by any herbicide treatments. Results from these trials verify that flumioxazin, napropamide, oryzalin, and pendimethalin at the tested rates would be appropriate options for weed control in newly planted blackberries. These results corroborate regional recommendations against the use of mesotrione in first-year blackberry plantings. The findings from this trial indicate that S-metolachlor would be safe for registration for use on blackberries because of its limited effect on crop injury and blackberry yield.

Nomenclature: Flumioxazin; mesotrione; napropamide; oryzalin; pendimethalin; S-metolachlor; blackberry, Rubus L. subgenus Rubus Watson

False cleavers (Galium spurium L.) is an aggressive weed from the Rubiaceae. Here we assemble a chromosome-scale draft of its genome, laying the foundations for determining the genetic basis of auxinic herbicide resistance and for systematic research into its polyphyletic genus. We use the genome to examine the population genetics of material from the Canadian Prairies and, in concert with a common greenhouse experiment, to examine whether the phenotypic variation observed in the field results primarily from genetic or environmental factors. The genome assembly covers approximately 85% of G. spurium's expected 360-Mbp genome size, with 94% of BUSCO (Benchmarking Universal Single-Copy Orthologs) genes complete and most single copy (89%). Approximately 37% of the genome is repetitive elements and 35,540 genes were annotated using RNA-seq data, including 100 homologues for genes involved in, or potentially involved in, herbicide resistance. The genome shows strong synteny with other members of the Rubiaceae, including smooth bedstraw (Cruciata laevipes Opiz) and robusta coffee [Coffea canephora (Pierre ex Froehner]. Double-digested RAD-seq data for the 19 populations from the Canadian Prairies indicated that G. spurium has high levels of population structure (F_ST = 0.54) and inbreeding (F_IS = 0.86) with low levels of hetrozygosity (H_O = 0.02) and nucleotide diversity (π = 0.0003). Variation in flowering time and seed weight largely overlapped among populations grown in the greenhouse. A redundancy analysis investigating genotype–phenotype associations showed few associations between single-nucleotide polymorphism (SNP) variation and these characteristics. In contrast, the majority of SNPs under selection were associated with mericarp hook density. This suggests that for most traits, environmental variation rather than genetic variation likely underlies phenotypic differences observed in the field. Several genes of interest, including several homologues involved in the assembly of the Skp1-Cullin-F-Box IR1/AFB E3 ubiquitin ligase complex (e.g., CAND1, ECR1), are located in areas of the genome with evidence of selection and are targets for further investigation.

Herbicide-resistant Italian ryegrass [Lolium perenne L. ssp. multiflorum (Lam.) Husnot] is a significant problem in multiple cropping systems because of its rapid growth, open pollination, prolific seed production, and multiple cases of resistance worldwide, except to protoporphyrinogen oxidase (PPO) inhibitors. This research evaluated tiafenacil, a new PPO inhibitor, in mixtures with glutamine synthetase- or acetyl-CoA carboxylase (ACCase)-inhibiting herbicides to manage resistant L. perenne ssp. multiflorum populations. Tiafenacil efficacy against L. perenne ssp. multiflorum was growth stage dependent, with increased efficacy at earlier stages in greenhouse studies. The LD₉₀ was 41.06 g ai ha–¹ at BBCH 23 and increased to 9.0-fold at BBCH 33. Field studies indicated that changes in carrier volume did not affect tiafenacil's efficacy; the highest tested rate of tiafenacil (75 g ai ha–¹) reduced L. perenne ssp. multiflorum inflorescence weight by 50% to 90%. Mixtures of tiafenacil and glufosinate (1,150 g ai ha–¹) improved L. perenne ssp. multiflorum control (+24% to 43%) and reduced inflorescence weight (+15% to 34%), particularly at the highest tested rates (50 and 75 g ai ha–¹), suggesting synergistic effects based on Colby's test. Tiafenacil with ACCase inhibitors improved L. perenne ssp. multiflorum control (+19% to 49%) and inflorescence weight reduction (+8% to 13%). These mixtures exhibited an additive effect when combined with fluazifop and a synergistic effect with clethodim. Herbicide mixtures and application strategies are critical to effective L. perenne ssp. multiflorum management. Tiafenacil, especially when used with glufosinate or ACCase inhibitors, offers an effective solution to L. perenne ssp. multiflorum management and is a strategic tool against herbicide resistance, as resistance to PPO inhibitors has not evolved. Further research should assess practices to ensure the long-term viability of these mixtures for resistance management.

Seventeen putative resistant late watergrass populations [Echinochloa phyllopogon (Stapf.) Koso-Pol.; syn.: Echinochloa oryzicola (Vasinger) Vasinger] originating from rice (Oryza sativa L.) monoculture fields in northern Greece were examined for possible evolution of multiple resistance to acetolactate synthase (ALS) and acetyl-CoA carboxylase (ACCase) inhibitors and auxin herbicides in rate–response pot assays. Most of the populations were highly cross-resistant to the ALS-inhibiting herbicides bispyribac-Na, imazamox, penoxsulam, and nicosulfuron + rimsulfuron, whereas three of them were also multiple resistant to both ALS and the auxin mimic quinclorac. In addition, two E. phyllopogon populations were found to be multiple resistant to the ALS and ACCase inhibitors cycloxydim, cyhalofop-butyl, profoxydim, and quizalofop-P-ethyl. Amplification and sequencing of the ACCase gene fragment from eight surviving profoxydim-treated plants of the two multiple-resistant E. phyllopogon populations to ALS- and ACCase-inhibiting herbicides, revealed an Ile to Leu substitution at codon 1781 of the ACCase enzyme. However, amplification and sequencing of the ALS gene fragment in the same E. phyllopogon plants sequenced for ACCase revealed a Trp to Leu substitution at codon 574 of the ALS enzyme in three out of the eight sequenced plants. These results strongly support the evidence of coexisting E. phyllopogon multiple target-site resistance to ALS and ACCase inhibitors, which is reported for the first time.

Numerous annual and perennial weeds infest sugarcane. End-season weed infestations are managed before sugarcane is replanted by fallowing (cultivation and sequential glyphosate applications) or by rotating to glyphosate-tolerant soybean in Louisiana. With the occurrence of perennial grasses and glyphosate-resistant weeds, growers need to utilize alternative late POST (LPOST) herbicide programs in soybean to reduce weed infestations in newly planted sugarcane (soybean-sugarcane rotation). Current rotational restrictions limit the use of acifluorfen, clethodim, fomesafen, and quizalofop to control troublesome weeds before soybean harvest and the subsequent planting of sugarcane. However, there is a lack of information on the carryover effects of these soybean herbicides on newly planted sugarcane. Field experiments were conducted at Schriever, LA, and St. Gabriel, LA, in 2017 to 2018 and in 2020 to 2021 to determine sugarcane injury and yield component response to herbicides labeled for LPOST applications in soybean, including acifluorfen, clethodim, fomesafen, lactofen, and quizalofop, applied at the field-use rates (1X) 45 d prior to or immediately after sugarcane planting. Separate field experiments were conducted at those two locations in Louisiana in 2018 to 2019 and in 2020 to 2021 to determine sugarcane injury and yield component response to five rates of fomesafen applied immediately after sugarcane planting. Results of the herbicide screening experiment showed no reductions in sugarcane shoot and stalk population, stalk height, sugarcane yield, sucrose content, or sucrose yield from the selected herbicides at either application timing. Fomesafen applied at 790 (2X) and 1,580 (4X) g ha^–1 resulted in 7% and 13% average visible injury to sugarcane at 27 d after treatment (DAT), respectively; injury symptoms persisted until 62 DAT. Transient injury observed at 62 DAT did not correspond to reduced sugarcane stalk population, height, sucrose content, sugarcane yield, or sucrose yield. This research indicates a potentially low risk of carryover and yield loss in newly planted sugarcane from late-season applications of selected soybean herbicides.

Nomenclature: Acifluorfen; clethodim; fomesafen; lactofen; quizalofop; soybean, Glycine max (L.) Merr; sugarcane, Saccharum spp. interspecific hybrids

There is limited information on the crop safety and weed control potential of commercially available PRE herbicides when applied under plastic mulch on various cucumber and summer squash cultivars grown in Florida. Two cucumber field trials were conducted at the Gulf Coast Research and Education Center in Wimauma, FL, in fall 2021 and spring 2022 to determine the effects of halosulfuron, pendimethalin, S-metolachlor, sulfentrazone, fomesafen, napropamide, oxyfluorfen, and flumioxazin on crop growth and development, yield, and the control of various weed species in the fields. We conducted this trial using three cucumber cultivars: ‘Speedway’, ‘Dominator’, and ‘Mongoose’. Two summer squash field trials were conducted simultaneously, evaluating all the mentioned herbicides, except flumioxazin, in addition to rimsulfuron on three summer squash cultivars: ‘Spineless Beauty’, ‘Payload’, and ‘Everglade’. In the cucumber trials, crop damage varied with cultivar and ranged from 3% to 16% in fall 2021. All herbicides caused ≥10% crop injury, except oxyfluorfen and flumioxazin, at 28 d after transplanting (DATr) in spring 2022. In the summer squash trial, halosulfuron, S-metolachor, and flumioxazin were the three most injurious PRE herbicides, causing more than 10% crop injury in seed-grown summer squash, with no effect of PRE herbicides on crop injury in transplant-grown summer squash in fall 2021. In spring 2022, crop injury with PRE herbicides varied with cultivar, where pendimethalin and S-metolachlor were consistently the most injurious PRE herbicides, causing 14% to 25% injury at 28 DATr. All PRE herbicides caused some damage to cucumber and summer squash, with limited differences between cultivars and no effect on overall crop yield.

Nomenclature: Flumioxazin; fomesafen; halosulfuron; napropamide; oxyfluorfen; pendimethalin; rimsulfuron; S-metolachlor; sulfentrazone; cucumber, Cucumis sativus L.; summer squash, Cucurbita pepo L.

Field studies were conducted in North Carolina to determine the critical period of weed control (CPWC) for Italian ryegrass in winter wheat. Soft red winter wheat was planted in late fall in 2017 and 2018 in no-till fields near Salisbury, NC. Treatments consisted of allowing weeds to grow from crop emergence for different intervals until removal (“weedy”), maintaining “weed-free” conditions from crop emergence for the same intervals, and then letting the weeds emerge and compete with the crop for the duration of the season. In 2017, weed removal occurred in 2-wk intervals from crop emergence up to 18 wk after crop emergence (WAE) and 3-wk intervals up to 18 WAE in 2018. Additional biological measurements, including Italian ryegrass density and height, were collected at 6, 12, and 18 WAE to characterize the effect of crop-weed interactions on the CPWC and weed populations. Nonlinear regression analysis was conducted to relate the timing of weed removal and yield loss. The analysis was carried out using growing degree days (GDDs) accumulated at corresponding WAE. Italian ryegrass density ranged from 292 to 824 plants m^–2, which created intense competitive conditions with wheat. In the absence of weed control, yield loss surpassed 60%. Using 5% yield loss as an accepted threshold, the CPWC for Italian ryegrass in no-till planted wheat was estimated to be from 1,100 to 1,900 GDD. This relatively short period makes it possible to reduce weed control intensity if control actions are properly timed.

Nomenclature: Italian ryegrass, Lolium perenne subsp. multiflorum Lam. Husnot.; wheat, Triticum aestivum L.

Herbicide-resistant weeds are fast becoming a substantial global problem, causing significant crop losses and food insecurity. Late detection of resistant weeds leads to increasing economic losses. Traditionally, genetic sequencing and herbicide dose-response studies are used to detect herbicide-resistant weeds, but these are expensive and slow processes. To address this problem, an artificial intelligence (AI)-based herbicide-resistant weed identifier program (HRIP) was developed to quickly and accurately distinguish common chickweed plants that are resistant to acetolactate synthase (ALS) inhibitor herbicides and those that are susceptible to ALS inhibitors. A regular camera was converted to capture light wavelengths from 300 to 1,100 nm. Full-spectrum images from a 2-yr experiment were used to develop a hyperparameter-tuned convolutional neural network model using a “train from scratch” approach. This novel approach exploits the subtle differences in the spectral signature of ALS inhibitor-resistant and ALS inhibitor-susceptible common chickweed plants as they react differently to the ALS-inhibiting herbicide treatments. The HRIP was able to identify ALS-inhibitor–resistant common chickweed as early as 72 h after treatment at an accuracy of 88%. It has broad applicability due to its ability to distinguish common chickweed plants that are resistant to ALS-inhibitor herbicides from those that are susceptible to becoming resistant to them regardless of the type of ALS herbicide or dose used. Using tools such as the HRIP will allow farmers to make timely interventions to prevent the herbicide-escape plants from completing their life cycle and adding to the weed seedbank.

Nomenclature: common chickweed, Stellaria media (L.) Vill.

Early soybean planting and cover crop adoption in the U.S. Midwest prompt investigation into the impact of these practices on weed community dynamics and best management practices. While previous research has explored different aspects of giant ragweed control, the specific integration among soil management practices, including cover crop adoption, soybean planting timing, and herbicide use, has not been thoroughly investigated. This study assessed the effects of soil management, soybean planting time, and preemergence (PRE) herbicide application on giant ragweed control and soybean yield in Wisconsin and Nebraska in 2022 and 2023. The study included a factorial arrangement of four soil management treatments (conventional tillage, no-till, and fall-planted cereal rye early terminated and terminated at planting [planting green]), two soybean planting times, and two PRE herbicide treatments (PRE and no PRE). POST herbicides were applied when ∼50% of giant ragweed plants within each treatment reached ∼10 cm in height. In Nebraska, cereal rye and tillage treatments without a PRE had at least 67% lower giant ragweed density than no-till at POST. In no-till, densities were at least 60% lower with PRE compared to no PRE. In Wisconsin, cereal rye did not reduce giant ragweed density at POST compared to no-till, likely due to relatively low biomass accumulation. In contrast, delayed soybean planting reduced giant ragweed density for most treatments but lowered soybean yield in no-till and planting-green treatments. The PRE herbicides had either no effect or positive effects on reducing giant ragweed density and increasing soybean yield. Overall, this study suggests that soil management and soybean planting timing are crucial for effective giant ragweed management in Wisconsin, where biotypes with a long emergence window during the spring and summer are present, while in Nebraska, soil management and soybean planting timing are less critical due to giant ragweed biotypes with an early and short emergence window in the spring.

Nomenclature: Giant ragweed, Ambrosia trifida L.; cereal rye, Secale cereale L.; soybean, Glycine max (L.) Merr.

Selection of effective herbicide strategies (i.e., one-pass versus two-pass and timing [preemergence versus postemergence]) is of great importance to corn growers. Field studies were conducted to evaluate overall end-of-season weed control efficacy of multiple herbicide strategies in conventional tillage corn production systems. These studies were carried out over six site-years at four locations in Wisconsin: Arlington (2018 and 2019), Brooklyn (2019), Lancaster (2019), and Janesville (2018 and 2019). Herbicide strategy treatments included one-pass preemergence, one-pass postemergence, two-pass preemergence followed by (fb) postemergence, and two-pass preemergence fb postemergence with layered residual herbicides. The weed species present at the experimental site-years included common lambsquarters, giant foxtail, giant ragweed, velvetleaf, and waterhemp. Except Arlington-2019, the herbicide strategy was not as influential for the site-years infested with common lambsquarters, giant foxtail, velvetleaf, and waterhemp species (e.g., Arlington-2018, Brooklyn-2019, Lancaster-2019), as effective overall end-of-season control (>90%) was achieved regardless of the herbicide strategy, and no significant differences were observed in the combined weed biomass across strategies. A two-pass strategy (e.g., preemergence followed by postemergence, or preemergence followed by postemergence with layered residual herbicides) was necessary for effective overall end-of-season control at the site-years infested with giant ragweed (Janesville-2018 and -2019). Weed interference reduced corn yield by 11% to 75% across site-years. Although certain weed communities can be effectively controlled by a one-pass herbicide strategy, two-pass strategies provided the greatest and most consistent overall end-of-season weed control and corn yield across all site-years, regardless of weed species composition and environmental conditions. Hence, a two-pass herbicide strategy is recommended for conventional-tillage corn production in Wisconsin to ensure effective end-of-season weed control while protecting yield potential of the crop, particularly in fields infested with moderate to high density of troublesome weeds such as giant ragweed.

Nomenclature: Acetochlor; bicyclopyrone; clopyralid; dicamba; flumetsulam; glyphosate; mesotrione; rimsulfuron; S-metolachlor; tembotrione; common lambsquarters, Chenopodium album L.; giant foxtail, Setaria faberi Herrm.; giant ragweed, Ambrosia trifida L.; velvetleaf, Abutilon theophrasti Medik.; waterhemp, Amaranthus tuberculatus (Moq.) J.D. Sauer; corn, Zea mays L.

Redweed is a tropical, erect branched herb, and one of the predominant broadleaf weeds affecting upland crops in the Onattukara Sandy Plains of Kerala, India. Experiments were conducted in a screenhouse in Thiruvananthapuram, Kerala, India, to determine the effects of seed burial depth and seed scarification on emergence indices and growth attributes of redweed. Scarification stimulated emergence and resulted in greater values for emergence indices and seedling parameters. The seedling emergence of redweed was influenced by seed burial depth. Shallow seed burial (2 cm) of scarified and non-scarified seeds resulted in greater seedling length (70 cm and 58 cm, respectively), seedling biomass (0.72 g and 0.48 g, respectively), emergence percentage (60% and 32%, respectively), and greater values for other emergence indices. As the depth of seed burial increased from 2 cm, emergence and seedling biomass decreased, exhibiting lower values for the emergence indices. Correlation and regression studies revealed that seed burial depth of scarified and non-scarified seeds greater than 2 cm had a negative effect on seedling emergence and biomass of redweed. Weed biology studies indicated that redweed displayed notable consistency in its phenological traits, regardless of the location where the seeds were collected, as little ecotype variability was observed. Emergence occurred in 6 d, 50% flowering in 44 d, capsule formation in 56 d, and maturity in 76 d. On average, a single plant produced 277 seeds and had a 100-seed weight of 0.31 g. A stale seedbed with shallow tillage or deep plowing to a depth of 10 cm before sowing can be adopted to reduce the infestation of redweed.

Nomenclature: Redweed, Melochia corchorifolia L.

Cotton producers need residual herbicides that can safely and practically be applied postemergence. Herbicide-coated fertilizers could allow for simultaneous application of residual herbicides and a bulk fertilizer blend. Therefore, a study was conducted in 2022 and 2023 in Fayetteville, AR, to evaluate cotton tolerance to 12 herbicide treatments coated onto a fertilizer blend and applied over cotton. Herbicides and rates evaluated included diuron at 840 g ai ha^–1, florpyrauxifen-benzyl at 29 g ai ha^–1, flumioxazin at 105 g ai ha^–1, flumioxazin ＋pyroxasulfone at 70 ＋ 90 g ai ha^–1, fluridone at 168 g ai ha^–1, fluometuron at 840 g ai ha^–1, fomesafen at 280 g ai ha^–1, pyroxasulfone at 128 g ai ha^–1, saflufenacil at 66 g ai ha^–1, saflufenacil ＋ dimethenamid-P at 25 ＋ 219 g ai ha^–1, saflufenacil ＋ pyroxasulfone at 44 ＋ 91 g ai ha^–1, and S-metolachlor at 1,388 g ai ha^–1. In both years, fluridone, fluometuron, diuron, and S-metolachlor caused less than 10% injury at 7 d after treatment (DAT). Higher injury levels were observed in 2022 (19% to 30%) compared with 2023 (4% to 12%) for flumioxazin, fomesafen, saflufenacil, saflufenacil plus dimethenamid-P, and saflufenacil ＋ pyroxasulfone. The elevated injury in one of two years was attributed to the presence of dew when the herbicide-coated fertilizer was applied. The initial injury was transient, as the cotton generally had recovered by 28 DAT for all herbicides. No differences in seed cotton yield or groundcover among the herbicide treatments occurred either year. These results highlight the potential of using several postemergence-applied, residual herbicides coated onto fertilizer that are not currently registered for over-the-top use in cotton.

Nomenclature: Dimethenamid-P; diuron; florpyrauxifen-benzyl; fluometuron; flumioxazin; fluridone; fomesafen; pyroxasulfone; saflufenacil; S-metolachlor; cotton; Gossypium hirsutum L.

Outdoor studies were conducted to determine the extent of leafy spurge biomass reduction resulting from broadcast application of 2,4-D (2,244 g ae ha–¹) with and without wiper-applied glyphosate. Glyphosate (575 g ae L^–1) was applied at 0%, 33%, 50%, and 75% diluted concentrate with a wiper 24 h after 2,4-D was broadcast-applied. Injury estimates and shoot biomass did not differ between plants treated with 2,4-D only or when glyphosate was wiper-applied 21 d after treatment. Shoot regrowth biomass of plants treated with 2,4-D only was approximately 560% greater than nontreated plants 3 mo after treatment. Plants treated with wiper-applied glyphosate exhibited shoot regrowth biomass of less than 10% compared with nontreated plants 3 mo after treatment. Root biomass of plants treated with 2,4-D only (160% of nontreated plants) exhibited a similar pattern of shoot regrowth biomass. Root biomass of plants treated with wiper-applied glyphosate exhibited approximately 50% reductions compared with nontreated plants. All vegetative metrics were equally reduced with all tested concentrations of glyphosate; therefore, all labeled concentrations should be effective. The results of the experiment indicate that broadcast-applied 2,4-D is more effective at reducing leafy spurge biomass with the addition of wiper-applied glyphosate.

Nomenclature: 2,4-D; glyphosate; leafy spurge; Euphorbia esula L.

Multiple herbicide classes–resistant (MHCR) kochia poses a serious concern for producers in the Central Great Plains, including western Kansas. Greenhouse and field experiments were conducted at Kansas State University Research and Extension Centers near Hays and Garden City, KS, to evaluate pyridate-based postemergence herbicide mixtures for controlling MHCR kochia. One previously confirmed MHCR population (resistant to atrazine, glyphosate, dicamba, and fluroxypyr) and a susceptible (SUS) kochia population were tested in a greenhouse study. The kochia population at Hays field site was resistant to atrazine, dicamba, and glyphosate, whereas the kochia population at the Garden City site was resistant to atrazine and glyphosate. Colby's analysis revealed synergistic interactions when pyridate was mixed with atrazine, dicamba, dichlorprop-p, fluroxypyr, glyphosate, or halauxifen/fluroxypyr and resulted in ≥94% control and shoot dry-biomass reduction of MHCR kochia in a greenhouse study. Similarly, synergistic interactions were observed for MHCR kochia control in fallow field studies at both sites when pyridate was mixed with glyphosate or atrazine. Kochia control was increased from 26% to 90% with the application of glyphosate + pyridate and from 28% to 95% with atrazine + pyridate at both sites as compared to separate applications of glyphosate or atrazine. This is the first report for such a strong synergistic effect for both glyphosate and atrazine mixtures with pyridate on a weed resistant to both. All other pyridate-based herbicide mixtures showed an additive interaction and resulted in better control of MHCR kochia (87% to 100%) as compared to their individual applications (23% to 92%) across both sites except 2,4-D. These results suggest that pyridate can play a crucial role in various postemergence herbicide mixtures for effective control of MHCR kochia.

Nomenclature: Atrazine; dicamba; dichlorprop-p; glyphosate; halauxifen/fluroxypyr; pyridate; kochia, Bassia scoparia (L.) A. J. Scott

Off-target herbicide drift away from rice is historically a concern in California, where susceptible crops such as orchards and vineyards are nearby. Tetflupyrolimet is a potent inhibitor of dihydroorotate dehydrogenase that provides excellent grass weed control in rice cropping systems. In efforts to steward tetflupyrolimet before its registration in California, this research was conducted to compare the onset of foliar symptoms from tetflupyrolimet applications onto almond, grapevine, peach, pistachio, plum, and walnut. Tetflupyrolimet was applied to these tree and vine crops at fractional rates of 1/200×, 1/100×, 1/33×, and 1/10× of the 125 g ai ha^–1 recommended use rate on rice. Almond, pistachio, and walnut trees also received 1× of the use rate. Tetflupyrolimet treatments were applied on one side of 3- to 4-yr-old almond, peach, pistachio, plum, and walnut trees, and on one side of 25- to 26-yr-old grapevines in 2022 and 2023. Visible injury ratings were carried out weekly to assess symptomology throughout the growing seasons and at leaf-out the following springs. Tree trunk diameter was recorded before and after herbicide applications. No injury was observed to any tested crops, regardless of the tetflupyrolimet application rate. In all orchard crops, tree trunk diameter was not affected by tetflupyrolimet treatments. Likewise, grape yield was not reduced even at the 1/10× tetflupyrolimet fractional rate. Since no injury symptoms were recorded, this research suggests that tetflupyrolimet can be safely used on nearby rice fields and might be a target for future registration consideration for use on orchard and vineyard crops.

Nomenclature: Tetflupyrolimet; almond, Prunus dulcis (Mill.) D.A. Webb; grapevine, Vitis vinifera L.; peach, Prunus persica (L.) Batsch; pistachio, Pistacia vera L.; plum, Prunus domestica L.; rice, Oryza sativa L.; walnut, Juglans regia L.

Waterhemp has become a serious management challenge for field crop growers in New York. Two putative glyphosate-resistant (GR) waterhemp populations (NY1 and NY2) were collected in 2023 from two soybean fields in Seneca County, NY. The objectives of this research were to 1) confirm and characterize the level of glyphosate resistance in waterhemp populations from New York relative to a known glyphosate-susceptible population from Nebraska (NE_SUS), and 2) evaluate the efficacy of various postemergence herbicides for GR waterhemp control. Based on the shoot dry weight reductions (GR₅₀ values) in a dose-response study, the NY1 and NY2 populations exhibited 5.6- to 8.3-fold resistance to glyphosate compared with the NE_SUS population. In a separate study, postemergence herbicides such as dicamba, glufosinate, lactofen, and 2,4-D applied alone or in a mixture with glyphosate or glufosinate had provided 89% to 99% control and ≥97% shoot dry weight reduction of NY1 and NY2 populations 21 d after treatment. Greater than 98% control of the NE_SUS population was achieved with tested postemergence herbicides, except mesotrione (62% control). Furthermore, atrazine, chlorimuron + thifensulfuron, and mesotrione were the least effective in controlling NY1 and NY2 populations (42% to 59% control and 50% to 67% shoot dry weight reductions, respectively). These results confirm the first report of GR waterhemp in New York. Growers should adopt effective alternative postemergence herbicides tested in this study to manage GR waterhemp.

Nomenclature: Atrazine; chlorimuron; dicamba; glufosinate; glyphosate; lactofen; mesotrione; thifensulfuron; 2,4-D; waterhemp; Amaranthus tuberculatus (L.)

The windmill palm is a distinctive outdoor ornamental palm adapted to cooler climates. Weeds pose significant challenges in palm nurseries, particularly during seedling and establishment stages. This research was conducted in a nursery with 5,500 windmill palm seedlings, starting in April 2014, when the palm trees were 3 yr old. Experiments were terminated in October 2018 when weed control was no longer necessary due to the advanced growth of the palm trees. The objectives of this study were to determine the weed composition and diversity, elucidate the effects of mechanical weed management (MWM) on growth rate of palm, and develop a sustainable program to maximize palm tree growth through effective weed management and soil tillage. Few herbicides are registered for nursery use in Türkiye, thus weed control was performed mechanically using garden hoeing machines between rows and hand hoeing for intrarow strips. The most common and dense weeds were purple nutsedge, annual mercury, and common purslane in summer and autumn, and burning nettle in winter and spring. In 2014, weed densities were 100, 127, and 145 weeds m^–2 for MWM, hand-weeding (HW), and nontreated (NT) plots, respectively. Transplanted palm seedlings required at least two, ideally three growing seasons of intensive weed control until the palm tree crowns block sunlight and suppress weed growth. The research indicated that palm trees in the MWM treatment had approximately 84 leaves and a height of 210 cm by October 2018, compared with 54 leaves and a height of 136 cm for HW, and 40 leaves and 100 cm height for NT. These results highlight the critical role of MWM in promoting optimal growth of Chinese windmill palms. Effective and sustainable weed management, combining MWM and HW, is essential for producing high-quality palm trees. The research provides valuable insights for nursery managers and contributes to best practices for cultivating windmill palm trees in similar climatic regions.

Nomenclature: Annual mercury; Mercurialis annua L. MERAN; burning nettle; Urtica urens L. URTUR; common purslane; Portulaca oleracea L. POROL; purple nutsedge; Cyperus rotundus L. CYPRO; Chinese windmill palm; Trachycarpus fortunei (Hook.) H. Wendl.

Glufosinate resistance was previously confirmed in three Palmer amaranth accessions from Arkansas (MSR1, MSR2, and CCR). Greenhouse screening results suggested the presence of multiple herbicide resistance. Therefore, this study aimed to determine the postemergence resistance profile of these three glufosinate-resistant Palmer amaranth accessions. Field experiments were also conducted to assess preemergence and postemergence herbicide options to control the accession with the highest glufosinate resistance level (MSR2). A dose-response assay with the three resistant accessions and two susceptible standards was conducted with the herbicides 2,4-D, atrazine, dicamba, diuron, fomesafen, glyphosate, imazethapyr, and mesotrione. The preemergence and postemergence field experiments with MSR2 evaluated 15 and 16 single active ingredients, respectively. The Palmer amaranth accessions that carried glufosinate resistance were also confirmed to be resistant to six other postemergence herbicides: 2,4-D, diuron, fomesafen, glyphosate, imazethapyr, and mesotrione. CCR is also resistant to dicamba. Therefore, accessions MSR1, MSR2, and CCR have evolved resistance to postemergence herbicides pertaining to seven sites of action. A shift toward increased tolerance to atrazine has also been observed among all resistant accessions. Overall, field preemergence treatments with atrazine, pyroxasulfone, or trifludimoxazin obtained the highest MSR2 control levels at all evaluation times and the lowest number of seedlings emerging at 3 and 6 wk after treatment. In the postemergence experiment, only paraquat obtained MSR2 control levels above 90% at all ratings. The lowest number of alive MSR2 plants was observed after postemergence treatments with paraquat or trifludimoxazin. Fields near where glufosinate resistance has been confirmed in Palmer amaranth will likely demand a more diverse and proactive management strategy that relies on combinations of chemical, cultural, and mechanical control tactics. Future efforts should focus on sequential applications and mixture, the elucidation of all resistance mechanisms in the evaluated accessions, and soil-applied dose-response.

Nomenclature: 2,4-D; atrazine; dicamba; diuron; fomesafen; glyphosate; imazethapyr; mesotrione; paraquat; pyroxasulfone; trifludimoxazin; Palmer amaranth; Amaranthus palmeri S. Watson

North Carolina growers have long struggled to control Italian ryegrass, and recent research has confirmed that some Italian ryegrass biotypes have become resistant to nicosulfuron, glyphosate, clethodim, and paraquat. Integrating alternative management strategies is crucial to effectively control such biotypes. The objectives of this study were to evaluate Italian ryegrass control with cover crops and fall-applied residual herbicides and investigate cover crop injury from residual herbicides. This study was conducted during the fall/winter of 2021–22 in Salisbury, NC, and fall/winter of 2021–22 and 2022–23 in Clayton, NC. The study was designed as a 3 × 5 split-plot in which the main plot consisted of three cover crop treatments (no-cover, cereal rye at 80 kg ha–¹, and crimson clover at 18 kg ha–¹), and the subplots consisted of five residual herbicide treatments (S-metolachlor, flumioxazin, metribuzin, pyroxasulfone, and nontreated). In the 2021–22 season at Clayton, metribuzin injured cereal rye and crimson clover 65% and 55%, respectively. However, metribuzin injured both cover crops ≤6% in 2022–23. Flumioxazin resulted in unacceptable crimson clover injury of 50% and 38% in 2021–22 and 2022–23 in Clayton and 40% in Salisbury, respectively. Without preemergence herbicides, cereal rye controlled Italian ryegrass by 85% and 61% at 24 wk after planting in 2021–22 and 2022–23 in Clayton and 82% in Salisbury, respectively. In 2021–22, Italian ryegrass seed production was lowest in cereal rye plots at both locations, except when it was treated with metribuzin. For example, in Salisbury, cereal rye plus metribuzin resulted in 39,324 seeds m^–2, compared to ≤4,386 seeds m^–2 from all other cereal rye treatments. In 2022–23, Italian ryegrass seed production in cereal rye was lower when either metribuzin or pyroxasulfone were used preemergence (2,670 and 1,299 seeds m^–2, respectively) compared with cereal rye that did not receive an herbicide treatment (5,600 seeds m^–2). cereal rye (Secale cereale L.) and crimson clover (Trifolium incarnatum L.)

Nomenclature: Flumioxazin; metribuzin; pyroxasulfone; S-metolachlor; cereal rye; Secale cereale L; crimson clover; Trifolium incarnatum L; Italian ryegrass; Lolium perenne L. ssp. multiflorum (Lam.) Husnot

Fluridone was registered for use in rice production in 2023, offering a new herbicide site of action for growers. However, little information is available on the degree of rice tolerance to this herbicide. Field experiments conducted in 2022 and replicated in 2023 near Colt, AR, evaluated the tolerance of 12 rice cultivars to fluridone, applied preemergence or at the 3-leaf growth stage, in separate experiments. Each experiment consisted of one cultivar. Fluridone rates included 0, 168 (1 × label rate), and 336 (2 × label rate) g ai ha–¹ in all experiments. Visible injury varied between years in all experiments, likely due to different environmental conditions. In 2022, injury following preemergence applications of fluridone was below 25% across cultivars. In contrast, in 2023, injury ≥30% occurred to five cultivars, with a maximum of 58% observed for the cultivar ‘DG263L’. In both years, only three cultivars exhibited injury ≥20% following fluridone applications at the 3-leaf stage. Fluridone negatively affected shoot density, groundcover, chlorophyll content, and days to 50% heading in most cultivars when applied preemergence. When fluridone was applied to 3-leaf rice, at least one of the variables evaluated was negatively affected in two and nine cultivars in 2022 and 2023, respectively. Grain yield reductions of at least 18% were observed from eight cultivars in 2022, and a grain yield decrease from 9% to 49% from eight cultivars occurred in 2023 in the preemergence experiments. Fluridone applied to rice at the 3-leaf stage did not cause a yield penalty to any cultivar in 2022, whereas in 2023, a yield loss occurred from eight cultivars. Yield loss from the DG263L cultivar occurred at the 1 × rate in both experiments, indicating that this cultivar appears to be sensitive to fluridone, regardless of the application timing. Based on these findings, fluridone tolerance is cultivar-dependent. Furthermore, preemergence applications of fluridone to rice should be avoided.

Nomenclature: Fluridone; rice; Oryza sativa L.

Tetflupyrolimet is the first herbicide with a novel site of action (SOA) labeled PRE and early POST for use in agronomic crops to be labeled in the last three decades. Direct-seeded paddy rice field experiments were conducted near Stuttgart, AR, on a silt loam soil and near Keiser, AR, on a clay soil to evaluate tetflupyrolimet-containing herbicide programs in comparison to commercial standards in conventional, imidazolinone-resistant, and quizalofop-resistant rice systems. Additionally, a furrow-irrigated rice experiment was conducted near Colt, AR, and Keiser to ensure weed control with clomazone and tetflupyrolimet mixtures compared to commercial standards. Twelve commonly planted rice cultivars were also evaluated in response to a single PRE or POST (2- to 3-leaf rice) application of tetflupyrolimet at 200 or 400 g ai ha–1 in a paddy rice system near Colt. When averaged over soil texture and site-year, all herbicide programs provided ≥98% barnyardgrass control at 56 d after (DA) the last application. Visible rice injury varied for each rice system. Still, injury rarely differed among herbicide programs, except at a single evaluation timing in the conventional (7 DA, 3- to 4-leaf applications) and quizalofop-resistant (preflood) systems. All 12 rice cultivars displayed high tolerance to a single PRE or POST application of tetflupyrolimet at 200 or 400 g ai ha–¹. No visible injury, stand loss, or negative impact on rice maturity or reduced grain yield was observed for any cultivar. Tetflupyrolimet will be an effective alternative SOA in a program approach for barnyardgrass while maintaining excellent rice crop safety.

Nomenclature: Clomazone; quizalofop; tetflupyrolimet; barnyardgrass; Echinochloa crus-galli (L.) P. Beauv.; rice; Oryza sativa L.

As mid-southern U.S. rice producers continue to adopt furrow-irrigated rice production practices, supplementary management efforts will be vital in combating Palmer amaranth due to the extended germination period provided by the lack of a continual flood. Previous research has revealed the ability of cover crops to suppress Palmer amaranth emergence in corn, cotton, and soybean production systems; however, research on cover crop weed control efficacy in rice production is scarce. Therefore, trials were initiated in Arkansas in 2022 and 2023 to evaluate the effect of cover crops across five site-years on rice emergence, groundcover, grain yield, and total Palmer amaranth emergence. The cover crops evaluated were cereal rye, winter wheat, Austrian winterpea, and hairy vetch. Cover crop biomass accumulation varied by site-year, ranging from 430 to 3,440 kg ha–¹, with cereal rye generally being the most consistent producer of high-quantity biomass across site-years. Rice growth and development were generally unaffected by cover crop establishment; however, all cover crops reduced rice emergence by up to 30% in one site-year. Rice groundcover was reduced by 13% from cereal rye in one site-year 2 wk before heading but cover crops did not affect rough rice grain yield in any of the site-years. Palmer amaranth emergence was reduced by 19% and 35% with cereal rye relative to the absence of a cover crop when rice was planted in April in Marianna, and May in Fayetteville, respectively. In most trials, Palmer amaranth emergence was not reduced by a cereal cover crop. In most instances, legume cover crops resulted in less Palmer amaranth emergence than without a cover crop. Based on these results, legume cover crops appear to provide some suppression of Palmer amaranth emergence in furrow-irrigated rice while having a minimal effect on rice establishment and yield.

Nomenclature: Palmer amaranth, Amaranthus palmeri (S.) Wats; Austrian winterpea, Pisum sativum L.; cereal rye, Secale cereale L.; corn, Zea mays L.; cotton, Gossypium hirsutum L.; hairy vetch, Vicia villosa Roth; rice, Oryza sativa L.; soybean, Glycine max (L.) Merr.; winter wheat, Triticum aestivum L.

Weeds belonging to the Amaranthus family are most problematic for soybean producers. With Palmer amaranth evolving resistance to multiple herbicides labeled for use in soybean, producers seek new sites of action to integrate into season-long herbicide programs. Bayer CropScience plans to launch a Convintro™ brand of herbicides, one being a premixture that will include diflufenican (categorized as a Group 12 herbicide by the Weed Science Society of America [WSSA]), metribuzin (WSSA Group 5), and flufenacet (WSSA Group 15), for use preemergence in soybean. Research trials were conducted in Fayetteville and Keiser, AR, and Holt, MI, in 2022 and 2023, to evaluate the premixture in a season-long program in a dicamba-resistant soybean system. A 0.17:0.35:0.48 ratio of a premixture of diflufenican:metribuzin: flufenacet (DFF-containing premixture) was applied preemergence with different combinations of glyphosate, glufosinate, dicamba, and acetochlor at 28 (early postemergence) and 42 (late postermergence) days after planting (DAP). At the early postemergence timing, the DFF-containing premixture provided >90% control of Palmer amaranth and prickly sida. However, common ragweed, common lambsquarters, morningglory ssp., and annual grass control was ≤80% at this timing. When the late postemergence applications occurred, treatments that had already received an early postemergence application controlled prickly sida, morningglory ssp., Palmer amaranth, and annual grasses to a greater extent than those that had not, indicating the preemergence application of the DFF-containing premixture was not sufficient to provide control of the weed spectrum through 42 DAP. By 70 DAP, all programs provided ≥93% control of all weeds evaluated. Herbicide programs that included the DFF-containing premixture preemergence followed by (fb) EPOST fb LPOST common ragweed, common lambsquarters, morningglory ssp., and annual grasses to a greater than the one-pass postemergence systems. In addition, all herbicide programs evaluated in this study reduced Palmer amaranth seed production by >99%. However, producers who plan to use the DFF-containing premixture may need two postemergence herbicide applications to obtain high levels of weed control throughout the growing season.

Nomenclature: Acetochlor; dicamba; diflufenican; flufenacet; glufosinate; glyphosate; metribuzin; annual grasses, Poaceae spp.; common lambsquarters, Chenopodium album L.; common ragweed, Ambrosia artemisiifolia L.; morningglory spp., Ipomoea ssp.; Palmer amaranth, Amaranthus palmeri (S.) Wats.; prickly sida, Sida spinosa L.; soybean; Glycine max (L.) Merr

Systematically monitoring the baseline sensitivity of troublesome weeds to herbicides is a crucial step in the early detection of their market lifespan. Florpyrauxifen-benzyl is one of the most important herbicides used in rice production throughout the world, and has been used for 5 yr in China. Barnyardgrass is one of the main targeted weed species of florpyrauxifen-benzyl. In total, 114 barnyardgrass populations were collected from rice fields in Jiangsu Province, China, and using whole-plant bioassays they were screened for susceptibility to florpyrauxifen-benzyl. The GR₅₀ values (representing the dose that causes a 50% reduction in fresh weight of aboveground parts) of florpyrauxifen-benzyl for all populations ranged from 1.0 to 34.5 g ai ha^–1, with an average of 6.8 g ai ha^–1, a baseline sensitivity dose of 3.3 g ai ha^–1, and a baseline sensitivity index of 34.5. Twenty-one days after treatment with florpyrauxifen-benzyl at the labeled dose (36 g ai ha^–1), 90% of the barnyardgrass populations exhibited >95% reductions in fresh weight of aboveground parts. Compared with the baseline sensitivity dose, 63, 44, and 7 populations had, respectively, no resistance (55%), low resistance (39%), and moderate resistance (6%) to florpyrauxifen-benzyl. Furthermore, the GR₅₀ distribution of barnyardgrass populations did not show a significant correlation with collection location, planting method (direct-seeding or transplanting), or rice species (Oryza sativa L. ssp. indica or ssp. japonica) at any of rice fields where seeds had been collected (P > 0.05). In conclusion, florpyrauxifen-benzyl remains effective for barnyardgrass control in rice fields despite serious resistance challenges.

Nomenclature: Barnyardgrass; Echinochloa glabrescens Munro ex Hook. f.; florpyrauxifen-benzyl; rice; Oryza sativa L.

Trifludimoxazin is a new herbicide that inhibits protoporphyrinogen oxidase and is being evaluated for the control of small-seeded annual broadleaf weeds and grasses in several crops. Currently, no information is available regarding peanut cultivar response to trifludimoxazin and its utility in peanut weed control systems. Three unique field experiments were conducted and replicated in time from 2019 through 2022 to determine the response of seven peanut cultivars (‘AU-NPL 17’, ‘FloRun 331’, ‘GA-06G’, ‘GA-16HO’, ‘GA-18RU’, ‘GA-20VHO’, and ‘TifNV High O/L’) to preemergence applications of trifludimoxazin and to determine the efficacy of trifludimoxazin at multiple rates and tank-mixtures with acetochlor, diclosulam, dimethenamid-P, pendimethalin, and S-metolachlor for weed management. Cultivar sensitivities to trifludimoxazin were not observed. Peanut density was not reduced by any trifludimoxazin rate. Compared with nontreated controls, in 2019 when trifludimoxazin was applied at 75 g ai ha^–1, leaf necrosis increased by 18% and peanut stunting increased by 10%, and yield was reduced by 6%. However, this rate increased leaf necrosis by only 4%, stunting by 3% to 5%, and it had no negative effect on yield in 2020–2021. Generally, peanut injury from preemergence-applied trifludimoxazin was similar to or less than that observed from flumioxazin at 2 wk after application (WAA). Peanut yield in the weed control study was reduced by 11% to 12% when treated with trifludimoxazin at 150 g ha^–1 (4× the standard rate) when compared to the 75 g ha^–1 rate. However, yield was not different from the flumioxazin treatment. Palmer amaranth control with trifludimoxazin combinations was ≥91% at 13 WAA, wild radish control was ≥96% at 5 WAA, and annual grass control was ≥97% at 13 WAA. Peanut is sufficiently tolerant of 38 g ha^–1 of trifludimoxazin, and when tank-mixed with other residual herbicides provides weed control similar to flumioxazin-based systems.

Nomenclature: Acetochlor; diclosulam; dimethenamid-P; flumioxazin; pendimethalin; S-metolachlor; trifludimoxazin; Palmer amaranth; Amaranthus palmeri S. Watson AMAPA; wild radish; Raphanus raphanistrum L. RAPRA; peanut; Arachis hypogaea L.

Increasing instances of herbicide-resistant annual bluegrass have limited turf managers' options for chemical control. Endothall inhibits serine threonine protein phosphatase, a novel site of action for warm-season turf, and endothall use in hybrid bermudagrass is not extensively reported. Greenhouse studies were conducted to evaluate herbicide-resistant annual bluegrass response to endothall. Five herbicide-resistant annual bluegrass biotypes were treated with increasing endothall rates and compared to two susceptible populations. One glyphosate-resistant annual bluegrass biotype was 2.3- to 3.3-fold more resistant to endothall depending on trial and susceptible biotype, and all other biotypes were endothall susceptible. Four field studies were established from 2022 to 2023 to evaluate the influence of endothall rate and application timing on bermudagrass and manilagrass turf injury and annual bluegrass control. These studies were arranged as a 3 × 4 factorial with three levels of application timing (fully dormant, 50% green, and 100% green) and four levels of herbicide (endothall applied at 1.12, 1.68, and 2.24 kg ai ha^–1 and trifloxysulfuron applied at 27.8 g ai ha^–1). Maximum observed turf injury was dependent on endothall rate and timing and was commercially acceptable (<30%) at the low and middle rates when applied to 100% green bermudagrass and at all rates when applied to dormant turf. When applied to 50% green turf (mid-transition), endothall unacceptably injured warm-season turf regardless of application rate. Endothall controlled annual bluegrass more effectively when applied during mid-transition and 100% green turf than it did when applied during fully dormant turf. When applied at rates of 1.68 and 2.24 kg ai ha^–1 during mid-transition or at 100% green turf, endothall controlled annual bluegrass 83% to 95%. Results from these studies indicate that endothall selectively controls herbicide-resistant annual bluegrass in warm-season turf but that selectivity and performance depend on application timing.

Nomenclature: Endothall; trifloxysulfuron; annual bluegrass, Poa annua L.; hybrid bermudagrass, Cynodon dactylon (L.) Pers. × Cynodon transvaalensis Burtt Davy. ‘Tifway 419’ and ‘Latitude 36’; manilagrass, Zoysia matrella (L.) Merr. ‘Cavalier’