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 received the equivalent rate of non-herbicide-treated AMS. Before top-dress, all plots (including the check) were treated with glyphosate and glufosinate to control previously emerged weeds. All herbicides resulted in transient cotton injury, except metribuzin. Cotton response to metribuzin varied by year and location. In 2022, metribuzin caused 11 to 39% and 8 to 17% injury at Clayton and Rocky Mount, 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 only comparable to linuron (790 kg ha-1). These findings research suggest, with the exception of metribuzin, residual herbicides coated on 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.

Alternative strategies to fumigation are needed to manage weeds and improve fruit yield in the annual hill plasticulture strawberry production system. Field experiments were conducted in Blackstone, Virginia, for two consecutive growing seasons, 2013/14 and 2014/15, to assess the efficacy of 4 wk and 8 wk soil solarization (SS) and mustard seed meal (MSM) at 1121 kg ha−1, alone and in combination, for weed control efficacy and crop yield estimation in an annual hill plasticulture strawberry production system. These treatments were compared to 1,3-dichloropropene (1,3-D) + chloropicrin (Pic) fumigation standard at 188 kg ha−1 and the 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, annual ryegrass, speedwell, common chickweed, and cudweed. The SS-4wk and MSM-4wk treatments did not affect weed density compared to UTC. The MSM-8 wk and 4 wk treatments reduced cumulative weed counts over UTC. In the second growing season, the total yield was significantly higher in the 1,3-D + Pic fumigation treatment compared with other treatments. The SS-4wk, MSM-4wk, and MSM-8wk treatments did not improve the total or marketable yield compared to UTC. The marketable yield in SS-MSM-8wk 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.

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 (WSSA Group 12), metribuzin (WSSA Group 5), and flufenacet (WSSA Group 15), for use preemergence (PRE) 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 of the diflufenican:metribuzin:flufenacet (DFF-containing) premixture was applied PRE with different combinations of glyphosate, glufosinate, dicamba, and acetochlor at 28 [early-postemergence (EPOST)] and 42 [late-postemergence (LPOST)] days after planting (DAP). At the EPOST timing, the DFF-containing premixture provided >90% Palmer amaranth and prickly sida control. However, common ragweed, common lambsquarters, morningglory ssp., and annual grass control was ≤80% at this timing. When the LPOST applications occurred, treatments that had already received an EPOST application controlled prickly sida, morningglory ssp., Palmer amaranth, and annual grasses greater than those that had not, indicating the PRE application of the DFF-containing premixture was not sufficient to provide control of the weed spectrum through 42 days after planting. By 70 days after planting, all programs provided ≥93% control of all weeds evaluated. Herbicide programs that utilized the DFF-containing premixture PRE fb EPOST fb LPOST controlled common ragweed, common lambsquarters, morningglory ssp., and annual grasses greater than the one pass postemergence systems. In addition, all herbicide programs evaluated reduced Palmer amaranth seed production by >99%. However, producers that plan to utilize the DFF-containing premixture may need two postemergence herbicide applications to obtain high levels of weed control throughout the growing season.

With Palmer amaranth and waterhemp evolving resistance to 9 and 6 different sites of action (SOA) globally, soybean producers continue to search for new options to control the 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). Plots treated with DFF-containing premixture had similar Palmer amaranth and waterhemp densities to the S-metolachlor:metribuzin premixture and the flumioxazin:pyroxasulfone:metribuzin premixture at 28 DAT. By 56 DAT, Palmer amaranth and waterhemp densities in plots with the DFF-containing premixture were comparable or superior to acetochlor and metribuzin and was comparable or superior to the S-metolachlor:metrbuzin premixture in five of six sites. The addition of dicamba or metribuzin to the DFF-containing premixture did not improve performance on Palmer amaranth and waterhemp over the DFF-containing premixture at 28 or 56 DAT. Overall, the DFF-containing premixture generally provided greater or comparable control to several standard herbicides, providing growers a new preemergence-applied product for control of Amaranthus species in soybean.

The continued development of herbicide-resistant weeds, such as Palmer amaranth, represents a growing concern across the United States Cotton Belt. To mitigate this issue, BASF Corporation developed Axant™ Flex cotton, the first quadruple-stacked herbicide resistance germplasm to improve the control of troublesome weed species in cotton. Field studies were conducted in 2022 and 2023 at the Texas Tech University Research Farm near New Deal, TX, to evaluate the response of Axant Flex cotton to topramezone applied alone or in combinations when applied to 3-leaf cotton (early-postemergence (EPOST)) or to 7-leaf cotton (mid-postemergence (MPOST)). No difference in cotton stand was observed between isoxaflutole or prometryn PRE treatments compared to the nontreated control. In 2022, no EPOST treatment caused greater than 6% crop response at 7 and 14 d after application (DAA). When treatments were made to 7-leaf cotton, crop response did not exceed 18% at 7 and 14 DAA. In 2023, crop response was ≤ 2% at 28 DAA regardless of application timing. No differences in lint yield were observed following any herbicide treatment when compared to the nontreated control in either year. Additionally, fiber length and strength were not adversely affected by treatments containing topramezone EPOST or MPOST in 2022 and 2023. These results support the potential use of topramezone in Axant Flex cotton to help manage troublesome weeds without detrimental effects on yield and fiber quality.

Municipalities are considering alternatives to traditional herbicides for suppressing weeds and vegetation in areas frequented by the public. Two field experiments were conducted to test the efficacy of alternative non-selective herbicides: one in Corvallis, Oregon, on a mixed lawn of perennial ryegrass, annual bluegrass, and broadleaf weeds, and another experiment in Las Cruces, New Mexico, on a predominantly bermudagrass lawn with broadleaf weeds. The experimental objective was to quantify and compare the effects of repeated applications of ten non-selective herbicides to terminate a lawn with mixed vegetation. Applications were made every two weeks for four applications starting on 15 April 2022 in Corvallis and 26 May 2022 in Las Cruces. Data collected included the percent green cover over time calculated using an area under the percent green cover progress curve (AUPGCPC), the percent green cover at the conclusion of the experiment, and the change in monocot and dicot density over the course of the experiment. All treatments resulted in a lower AUPGCPC compared to water only except for mint oil + sodium lauryl sulfate + potassium sorbate. The only treatments with an average percent green cover less than 50% was a combination of ammoniated soap of fatty acids + maleic hydrazide (47% green cover) in Corvallis and pelargonic acid (38%) in Las Cruces, suggesting that more applications would be needed to terminate the lawn under similar circumstances. At the conclusion of the experiment, the water only plots averaged 90% and 93% green cover in Corvallis and Las Cruces, respectively. The change of monocot and dicot densities over the course of the experiment indicated that some of the products tested may be more sensitive to dicots, or in some cases monocots, suggesting a potential for future selective herbicide research in certain locations and climates.

This study assessed dichlobenil’s potential to manage hair fescue in lowbush blueberry when targeted or broadcast-applied (7000 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 (2240 g ai ha-1). Targeted and broadcast-applied dichlobenil in fall 2020 significantly reduced average total tuft density in the non-bearing 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 non-bearing 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 each control, pronamide, targeted, and broadcast-applied dichlobenil, respectively. Increases in yield were not significant, though the large variation within the sample is the likely cause. The similarities between targeted and broadcast-applied treatments demonstrate the potential of targeted dichlobenil. Given the high product cost of dichlobenil at $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 developing a mechanized precision targeted applicator for use in the lowbush blueberry cropping system.

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 micro-encapsulated (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 showed 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 days after transplanting (DAT), whereas herbicide-treated plots exhibited weed cover at or below 10% by 28 DAT. 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 chloroacetamides post-transplanting, either as tank mixture or in sequence resulted in ≥19% injury. Despite the effective weed control achieved with herbicide treatments, mixing herbicides post-transplanting 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.

Bayer CropScience anticipates launching several premixtures for use in soybean, targeted at control of Palmer amaranth. One of the premixtures will contain diflufenican (WSSA Group 12), metribuzin (Group 5), and flufenacet (Group 15) (DFF-containing premixture), offering an alternative site of action for soybean producers. Field experiments were conducted in Arkansas and Michigan to evaluate application timings of the DFF-containing premixture for soybean tolerance and weed control and possible cultivar tolerance differences to diflufenican and the DFF-containing premixture. Soybean injury from the 1X and 2X rates of the DFF-containing premixture ranged from 0% to 60% 14 d after planting (DAP), with injury increasing the closer the herbicide was applied to soybean emergence. Excluding the 2X rate applied 3 DAP in Arkansas in 2023, soybean injury was <20% regardless of location, site year, application timing, and rate. For weed control experiments, only a 1X rate of the DFF-containing premixture was applied at the various application timings. Control of five weed species, encompassing broadleaves and grasses, ranged from 81% to 98%, regardless of application timing by 28 DAP. By 42 DAP, weed control ranged from 71% to 97%, with the 14-d preplant application timing typically being the least effective. The DFF-containing premixture and diflufenican alone were applied PRE at 1X and 2X rates for the soybean cultivar study. Soybean metribuzin sensitivity did not affect the degree of crop response, even on a high pH soil, and injury to soybean never exceeded 20%. Overall, the DFF-containing premixture will be a tool that soybean producers can integrate into a season-long herbicide program for use across the United States regardless of the soybean cultivar.

Italian ryegrass control is one of the most significant limitations in wheat production in the U.S. 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, while 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 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.

Bermudagrass is the most troublesome and difficult-to-control perennial grass weed in Florida sugarcane. Once established, it is only controlled effectively during the sugarcane fallow period using nonselective herbicides and tillage combinations. It is important to evaluate options for selective management of bermudagrass that escape sugarcane fallow period management programs to mitigate its progressive increase as the crop cycle increases from plant cane to ratoon crops. Greenhouse and field studies were conducted in Belle Glade, Florida, from 2017 to 2018 to determine the response of newly established bermudagrass from sprigs with stolons to two or three sequential applications of topramezone (25 and 50 g ha-1) every 14 d and the combinations of topramezone (25 and 50 g ha-1 ) with photosystem II (PS II)-inhibitor herbicides atrazine (2,240 g ha-1), ametryn (440 g ha-1), and metribuzin (2,240 g ha-1). Two or three sequential applications of topramezone with a cumulative total of 75 to 100 g ha-1 provided >93% bermudagrass control 42 d after the first sequential application under greenhouse and field conditions. These treatments had 12% chance of survival 70 d after the first sequential application. There was an additive effect of PS-II inhibitor herbicides on bermudagrass control in mixtures with topramezone. The mixture of topramezone (50 g ha-1) with metribuzin and atrazine provided more than 87% and 92% bermudagrass control under greenhouse and field conditions, respectively, 42 d after treatment. Bermudagrass treated with topramezone (50 g ha-1) mixture with metribuzin had 23% chance of survival 70 d after treatment. The results show good efficacy of sequential topramezone applications every 14 d or mixtures with PS-II inhibitor herbicides atrazine and metribuzin for control of newly established bermudagrass which typically escape control measures during the sugarcane fallow management period.

Herbicide-resistant Palmer amaranth is creating additional challenges for producers choosing 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 control Palmer amaranth effectively in cotton production systems and was recently registered for use in rice. Experiments were initiated in 2022 and 2023 to evaluate 1) Palmer amaranth control and rice tolerance to preemergence- and postemergence-applied fluridone at a 0.5x (84 g ai ha-1) and 1x rate (168 g ai ha-1) on a silt loam soil and 2) the effect of various herbicide programs containing fluridone on Palmer amaranth biomass, seed production, and rough rice grain yield. Preemergence applications of fluridone at a 1x 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.

In Georgia plasticulture vegetable production, a single installation of plastic mulch is utilized for up to five cropping cycles over an 18-month period. Preplant applications of glyphosate and glufosinate ensure fields are weed-free before transplanting, but recent data suggest residual activity of these herbicides may pose a risk to transplanted vegetables. Glyphosate and glufosinate were applied preplant in combination with three different planting configurations, including 1) a new plant hole into new mulch, 2) a pre-existing plant hole, 3) or a new plant hole spaced 15 cm from a pre-existing plant hole (adjacent). Following herbicide application, overhead irrigation was utilized to remove residues from the mulch before punching transplanting holes for tomato, cucumber, or squash. Visible injury, widths, biomass, yield of tomato, cucumber, or squash were not influenced by herbicide in the new mulch or adjacent planting configurations. When glyphosate was applied at 5.0 kg ae ha-1 and the new crop was planted into pre-existing holes, tomato was injured 45%, with reduced heights, biomass, and yields; at 2.5 kg ae ha-1 injury of 8% and a biomass reduction was observed. Cucumber and squash were injured 23% to 32% by glyphosate at 5.0 kg ae ha-1, with reductions in growth and early-season yield; lower rates did not influence crop growth or production when the crop was placed into a pre-existing plant hole. Glufosinate at the same rates did not affect tomato growth or yield when planted into pre-existing plant holes. Cucumber, when planted into pre-existing plant holes, was injured 43 to 75% from glufosinate, with reductions in height and biomass, and yield losses at 1.3 and 2.6 kg ai ha-1; similar results from glufosinate were observed in squash. In multi-crop plasticulture production, growers should ensure vegetable transplants are placed a minimum of 15 cm away from soil exposed to these herbicides.

Palmer amaranth resistant to dicamba, glufosinate, and protoporphyrinogen oxidase inhibitors has been documented in several southern states. With extensive use of these and other herbicides in South Carolina, a survey was initiated in the fall of 2020 and repeated in the fall of 2021 and 2022 to determine the relative response of Palmer amaranth accessions to selected preemergence (PRE) and postemergence (POST) herbicides. A greenhouse screening experiment was conducted where accessions were treated with three PRE (atrazine, s-metolachlor, and isoxaflutole) and six POST (glyphosate, thifensulfuron-methyl, fomesafen, glufosinate, dicamba, 2,4-D) herbicides at the 1× and 2× use rates. Herbicides were applied shortly after planting (PRE) or at the 2 to 4 leaf growth stage (POST). Percent survival was evaluated 5-14 days after application depending on herbicide activity. Sensitivity to atrazine PRE was lower for 49 and 33 accessions out of 115 to atrazine PRE at the 1× and 2× rate, respectively. Most of the accessions (90%) were controlled by isoxaflutole PRE at the 1× rate. Response to S-metolachlor PRE indicated 34% of the Palmer amaranth accessions survived the 1× rate (>60% survival). There were 11 accessions with reduced sensitivity to fomesafen POST; however, these percentages were not different from the 0% survivor group. Glyphosate POST at the 1× rate did not control most accessions (79%). Palmer amaranth response to thifensulfuron-methyl POST varied across the accessions, with only 36 and 28% controlled at the 1× and 2×rate, respectively. All accessions were controlled by 2,4-D, dicamba, or glufosinate POST. Palmer amaranth accessions from this survey exhibited reduced susceptibility to several herbicides commonly used in agronomic crops in South Carolina. Therefore, growers should continue to utilize multiple management tactics to minimize the evolution of herbicide resistance in Palmer amaranth in South Carolina.

New technologies in grain sorghum allow for the use of multiple acetyl CoA carboxylase- (ACCase) or acetolactate synthase- (ALS) inhibiting herbicides for johnsongrass control. With the growing issue of herbicide resistance, producers need to understand which herbicides will successfully control johnsongrass accessions. To determine the efficacy of herbicides recently registered or ones with potential to become available for use in grain sorghum, johnsongrass seeds were collected from 2017 to 2021 in Arkansas, Kansas, Texas, and Oklahoma and were screened for sensitivity to fluazifop, quizalofop, nicosulfuron, and imazamox. Additionally, glyphosate sensitivity was evaluated because of its use before planting or postharvest. Quizalofop resulted in 100% mortality of all johnsongrass accessions. Of the johnsongrass accessions evaluated, 89% were completely controlled with glyphosate. The ALS inhibitors nicosulfuron and imazamox resulted in 100% mortality of all Oklahoma accessions, but failures occurred on samples from other states. One accession from Kansas, 12 from Texas, and eight from Arkansas were found to have reduced sensitivity to nicosulfuron and imazamox. If producers plan to plant grain sorghum in areas with johnsongrass populations, an ACCase-inhibitor herbicide will most likely provide effective control. Imazamox and nicosulfuron, in conjunction with the appropriate trait, can be utilized in areas with sensitive johnsongrass populations or where other sensitive grass species are present.

Trifludimoxazin is a novel protoporphyrinogen oxidase (PPO)-inhibiting herbicide currently under development for foliar and residual control of several problematic weeds in preplant applications for soybean production. Field experiments were conducted in 2017 and 2018 to evaluate the foliar efficacy of trifludimoxazin applied alone and in combination with other herbicides on waterhemp, giant ragweed, and horseweed. Foliar applications of trifludimoxazin alone at 12.5 or 25 g ai ha-1 were highly efficacious on glyphosate-resistant waterhemp (94 to 99% control, respectively), moderately effective on giant ragweed (78 to 79% control, respectively), and resulted in minor efficacy on horseweed (≤ 20% control). Combinations of trifludimoxazin with glufosinate, glyphosate, paraquat, or saflufenacil remained highly effective (≥ 91% control) on waterhemp and giant ragweed. All herbicide mixtures with trifludimoxazin applied to horseweed were classified as additive interactions. Greenhouse experiments and Isobole analysis indicated trifludimoxazin mixtures with glyphosate and glufosinate on waterhemp and giant ragweed were additive. Mixtures of trifludimoxazin plus paraquat were slightly antagonistic under greenhouse conditions when applied to either waterhemp or giant ragweed, whereas trifludimoxazin plus saflufenacil was synergistic when applied to giant ragweed. Overall, trifludimoxazin applied alone at 12.5 or 25 g ha-1 was effective for managing waterhemp, and to an extent, giant ragweed, but not horseweed in preplant burndown applications. Furthermore, the addition of glufosinate, glyphosate, paraquat, or saflufenacil to applications of trifludimoxazin does not appreciably reduce weed control for these mixtures. As such, applications of trifludimoxazin alone and in combination with these herbicides may be utilized for effective preplant management of several problematic weeds in soybean.

A pre-launch survey of broadleaf weeds was conducted to predict the weed management efficacy of a novel genetically engineered sugar beet with resistance traits for glyphosate, dicamba, and glufosinate. We targeted problematic broadleaf weed species prevalent in the sugar beet system, including kochia, common lambsquarters, Palmer amaranth, and redroot pigweed across sugar beet areas in Colorado, Nebraska, and Wyoming. The results revealed that a significant percentage of kochia populations in Colorado, Nebraska, and Wyoming exhibited resistance to glyphosate (94%, 98%, and 75%, respectively) and dicamba (30%, 42%, and 17%, respectively). Palmer amaranth populations had resistance frequencies for glyphosate and dicamba of 80% and 20% in Colorado and 20% and 3% in Nebraska, respectively. No resistance to the tested herbicides was identified in common lambsquarters or redroot pigweed. Glufosinate resistance was not identified for any species. Kochia and Palmer amaranth populations from Colorado and Nebraska exhibited glyphosate resistance primarily through 5-enolpyruvylshikimate 3-phosphate synthase (EPSPS) gene amplification. However, one glyphosate-resistant kochia population from Wyoming lacked EPSPS gene amplification, indicating the presence of an alternative resistance mechanism. We identified the previously characterized IAA16 G73N substitution in a dicamba-resistant kochia population from Nebraska. However, dicamba-resistant kochia populations from Colorado did not possess this substitution, suggesting an alternative, yet-to-be-determined resistance mechanism. The widespread prevalence of glyphosate and dicamba resistance, coupled with the emergence of novel resistance mechanisms, poses a significant challenge to the long-term efficacy of this novel genetically engineered sugar beet technology. These findings underscore the urgent need for integrated weed management (IWM) strategies that diversify effective herbicide sites-of-action and incorporate alternative weed management practices within cropping systems.

Palmer amaranth is a troublesome weed species displaying the ability to adapt and evolve resistance to multiple herbicide modes of action, and there is a need for additional weed suppression tactics. Growing interest in the use of cover crops (CC) has led to questions regarding the most appropriate forms of CC management prior to cash crop planting in order to maximize weed suppression benefits. Experiments were conducted between 2021 to 2023 to test: 1) cover crop termination timing (i.e., green or brown), 2) CC biomass amount and 3) CC termination method (i.e., rolled or left standing) on Palmer amaranth suppression. Treatments included “planting brown” (cereal rye terminated two weeks before soybean planting), “planting green” (cereal rye terminated at soybean planting), and a no CC (winter fallow) check. Palmer amaranth emergence was evaluated at 4 and 6 weeks after soybean planting, and yield was calculated at harvest. CC reduced Palmer amaranth emergence when compared to the no CC check, and more suppression was observed as CC biomass increased. This decrease in emergence is potentially due to a decrease in light penetration reaching the soil surface and physical suppression as CC biomass increased. Yield, however, was unaffected by any CC management practice, indicating that growers can tailor CC termination practices for weed suppression. This information will provide better recommendations for farmers interested in using cover crops for weed suppression. Overall, the importance of CC biomass accumulation to achieve weed suppression is highlighted in our findings. Additionally, we add to the growing body of documentation that soybean yield may be variable from year to year as a result of CC presence.

Rice producers battle herbicide-resistant weeds worldwide while producing rice for ≥50% of the world’s population. Oxyfluorfen can provide rice producers with an alternative site of action for barnyardgrass control, as there are no documented cases of grass weeds being resistant to the herbicide in the midsouthern United States. Oxyfluorfen is anticipated to be labeled in the Roxy Rice Production System and may be sold as a clomazone:oxyfluorfen premixture; hence, experiments were conducted in 2021 and 2022 to evaluate preemergence-applied clomazone:oxyfluorfen ratios compared to clomazone alone on silt loam and clay soils. All ratios of the herbicides caused less than 7% injury to rice in two of four site-years on silt loam soils, whereas, in the two other site-years, the mixtures caused 10% to 40% rice injury at all observation timings. All combinations of the two herbicides provided at least 73% barnyardgrass control 5 weeks after rice emergence (WAE) in three of the four site-years on silt loam soils. In at least two of four site-years at 1 and 3 WAE, barnyardgrass control was improved when oxyfluorfen was added to clomazone compared to clomazone alone. On clay soil, barnyardgrass control in both site-years was ≥77% at 5 WAE for all clomazone and oxyfluorfen ratios. Injury to rice ranged from 13% to 30% for all treatments containing clomazone and oxyfluorfen in one of two site-years on clay soil at all observation timings. At 7 WAE, contrasts indicated that the 1:3 ratio of clomazone to oxyfluorfen provided greater barnyardgrass control than the 1:1.5 and 1:2 ratios in one of two site-years. Based on these findings, oxyfluorfen would improve the consistency of barnyardgrass control over clomazone alone in some instances. However, there is an increased risk of injury to rice with the addition of oxyfluorfen.

Greenhouse studies were conducted from 2020 to 2021 to evaluate the effect of simulated drift rates of 2,4-D and dicamba on strawberry growth, fruit development and fruit quality in Raleigh, NC. Treatments included 2,4-D choline and dicamba DGA plus Vapor Grip at 1/2x, 1/20x, and 1/200x of the 1x field rate of 1.09 and 0.8 kg ae ha-1, respectively. Treatments were applied to strawberry at three reproductive stages, including bud, flower, and fruit. Averaged across both herbicides, strawberry canopy size was reduced by the 1/2x rate 18, 25, 30, and 36% at 3, 6, 9, and 11 wk after treatment (WAT). The 1/2x rate of both herbicides caused greater injury to strawberry than the 1/20x or 1/200x, with maximum stunting from 2,4-D and dicamba of 54 and 36%, respectively. Fruit pH and SSC increased due to the 1/2x rate of dicamba compared to the 1/20x and 1/200x rates and the nontreated. Treated fruit (across all herbicides) were larger than fruit developing following herbicide application to flowers or buds but were similar to nontreated fruit.