Bearded sprangletop is a problematic native grass weed in California’s rice fields. The widespread and extensive use of acetyl-CoA carboxylase (ACCase)–inhibiting herbicides, such as cyhalofop-p-butyl (cyhalofop), has led to speculation that biotypes of bearded sprangletop have developed herbicide resistance to ACCase. The aim of this study was to evaluate suspected resistant bearded sprangletop biotypes, R1, R2, R3, and the susceptible biotype, S1, in terms of their levels of resistance to three ACCase-inhibiting herbicides and to characterize the molecular mechanisms of resistance. Dose–response experiments suggested that the biotype R1, R2, and R3 had high-level resistance to cyhalofop and to quizalofop-p-ethyl (quizalofop), but not clethodim. The study determined that the resistance to ACCase inhibitors was a target-site mechanism resulting from nucleotide substitution. The carboxyl transferase (CT) domain of the ACCase gene’s sequence analysis revealed the substitutions Trp-2027-Cys for R1 and R2 biotypes and Ile-2041-Asn for the R3 biotype. This study revealed the presence of target-site resistance to cyhalofop and quizalofop in at least two mutation points in representative biotypes of bearded sprangletop in California. This research highlights the significance of careful herbicide selection due to weed species responding quite rapidly to selection pressure, so as to aid in managing bearded sprangletop in rice fields.

The sustainable management of herbicides is critical to modern agriculture and the environment. This article examines the evolution and environmental implications of herbicide use in Saskatchewan, Canada, agriculture. It quantifies changes in herbicide use and their environmental impacts by analyzing farm-level herbicide use data from 1991 to 1994 and from 2016 to 2019 through the environmental impact quotient. Results confirm significant reductions in both environmental and toxicological impacts of herbicides used, underlining the pivotal shift from tillage-based weed control to herbicide-resistant cropping systems. The environmental impact of the top five herbicides (glufosinate, glyphosate, clethodim, imazamox, and 2,4-D) used from 2016 to 2019 is 65% lower than that for those herbicides (MCPA, 2,4-D, bromoxynil, diclofop-methyl, and trifluralin) used from 1991 to 1994, with a 45% reduction in the active ingredient applied per acre. Despite increased herbicide use due to more crop acres being seeded, the findings highlight a marked improvement in the sustainability of herbicide use, affirming the importance of technological advancements in agriculture. This research contributes valuable insights into long-term trends in herbicide use, offering a practical framework for informed decisions aligning with sustainable agricultural practices as well as reduced biodiversity impacts.

Weed management in cantaloupe and other melon crops is important to maximize fruit yield; however, there are few registered herbicides available in California. Several independent herbicide trials were conducted at University of California field stations in Davis (Yolo County), Five Points (Fresno County), and Holtville (Imperial County) from 2013 to 2019 to evaluate both registered and unregistered herbicides and incorporation methods (sprinklers, cultivation, or none) for crop safety and weed control in melons. Although specific treatments varied among locations depending on local practice and research objectives, ethalfluralin and halosulfuron were used in all experiments, and bensulide and S-metolachlor were evaluated in 4 of 6 site-years. Additional herbicides included clethodim, clomazone, DCPA, napropamide, pendimethalin, sethoxydim, and sulfentrazone. Among registered herbicides, halosulfuron, halosulfuron + ethalfluralin, and ethalfluralin + bensulide combinations provided consistently beneficial weed control across all site-years compared to the nontreated control. S-metolachlor performed as well as the best of the registered herbicides tested at each site-year; although moderate injury was noted at the Davis location, this did not reduce melon yield. The method used to incorporate preplant herbicides had a significant impact on weed control efficacy but varied by location. Mechanical incorporation of preplant herbicides resulted in improved weed control and yield compared to sprinklers. Early-season weed control, whether by herbicides or hand weeding, resulted in significant yield increase in most site-years.

Downy brome is a troublesome facultative winter-annual grass weed that invades agricultural and nonagricultural lands in western North America and can cause substantial crop yield losses particularly in no-till winter wheat. Glyphosate-resistant (GR) downy brome was identified in southern Alberta in 2021, representing the first confirmation of a GR grass weed in Canada. This study was designed to evaluate alternative herbicides and herbicide mixtures applied postemergence (POST) for control of GR and glyphosate-susceptible (GS) downy brome populations at the seedling stage under a controlled environment. The GR downy brome did not exhibit cross-resistance to other herbicides applied POST. Quizalofop alone or in combination with imazamox, imazamox + bentazon, or imazamox/imazethapyr, and glufosinate mixed with either clethodim or tiafenacil resulted in ≥80% visible control, plant mortality, and reduction in biomass of both GR and GS downy brome populations 21 d after treatment. Diligent stewardship of these remaining herbicide options is warranted since downy brome populations with resistance to herbicides that inhibit acetyl-CoA carboxylase or acetolactate synthase have been reported in neighboring states.

Water is the primary carrier for herbicide applications. Spray water qualities such as pH, hardness, temperature, or turbidity can influence herbicide performance and may need to be amended for optimum weed control. Water quality factors can affect herbicide activity by reducing solubility, enhancing degradation in the spray tank, or forming herbicide-salt complexes with mineral cations, thereby reducing the absorption, translocation, and subsequent weed control. The available literature suggests that the effect of water quality varies with herbicide chemistry and weed species. The efficacy of weak-acid herbicides such as glyphosate, glufosinate, clethodim, sethoxydim, bentazon, and 2,4-D is improved with acidic water pH; however, the efficacy of sulfonylurea herbicides is negatively impacted. Hard-water antagonism is more prevalent with weak-acid herbicides, and trivalent cations are the most problematic. Spray solution temperature between 18 C and 44 C is optimum for some weak-acid herbicides; however, their efficacy can be reduced at relatively low (5 C) or high (56 C) water temperature. The effect of water turbidity is severe on cationic herbicides such as paraquat and diquat, and herbicides with low soil mobility such as glyphosate. Although adjuvants are recommended to overcome the negative effect of spray water hardness or pH, the response has been inconsistent with the herbicide chemistry and weed species. Moreover, information on the effect of spray water quality on various herbicide chemistries, weed species, and adjuvants is limited; therefore, it is difficult to develop guidelines for improving weed control efficacy. Further research is needed to determine the effect of spray water factors and develop specific recommendations for improving herbicide efficacy on problematic weed species.

Rigid ryegrass is a problematic weed species in winter crops and winter fallow; however, recently, this weed species has been observed in summer crops and fallow. These observations warrant the evaluation of different postemergence herbicides for its control. Outdoor pot studies were conducted during the spring and summer of 2021 to 2022 to determine the performance of POST herbicides on two summer-emerging (S3 and S6) and two winter-emerging (W3 and W8) accessions of rigid ryegrass. Across all accessions, butroxydim, clethodim, paraquat, and paraquat + amitrole at the field rate provided complete control of rigid ryegrass. Both summer-emerging accessions were found to be resistant to the field rates of glufosinate (750 g ai ha−1), glyphosate (454 g ae ha−1), haloxyfop (52 g ai ha−1), and pinoxaden (30 g ai ha−1). The S6 accession had the highest dose required for a 50% reduction in biomass for these herbicides (glufosinate 1,120 g ai ha−1, glyphosate 1,210 g ae ha−1, haloxyfop 140 g ai ha−1, and pinoxaden 55 g ai ha−1). This summer-emerging accession (S6) was also resistant to iodosulfuron. All four accessions were found susceptible to imazamox + imazapyr (a commercial mixture) and mesosulfuron. The study provides the first evidence of poor control of summer-emerging accessions of rigid ryegrass with different herbicides. Multiple-herbicide-resistant summer-emerging rigid ryegrass accessions would be a challenge to the production of summer crops (e.g., cotton and sorghum) as well as winter crops that rely on weed-free summer fallows for soil moisture retention; therefore these accessions warrant diversified management strategies.

Field and pot experiments were conducted in Greece to study the occurrence of resistance in silky windgrass to acetolactate synthase (ALS)- and acetyl-CoA synthase (ACCase)-inhibiting herbicides. Twenty-four populations of silky windgrass were examined in whole-plant response experiments. High levels of field-evolved resistance to chlorsulfuron (0% to 28% control in terms of fresh weight reduction) with the recommended field rates were confirmed in most silky windgrass populations. However, other ALS inhibitors, such as pyroxsulam and a premix of mesosulfuron-methyl and iodosulfuron, provided adequate control (76% to 100% in terms of fresh weight reduction) of most populations, except eight silky windgrass populations that were found to be cross-resistant to all ALS-inhibiting herbicides tested (i.e., chlorsulfuron, commercial mixture of mesosulfuron-methyl plus iodosulfuron, and pyroxsulam). Conversely, most silky windgrass populations were controlled effectively (90% to 100% in terms of fresh weight reduction) with the recommended field rates of ACCase inhibitors cycloxydim, clethodim, and pinoxaden, but five populations were also found to be resistant to clodinafop-propargyl (10% to 68% control in terms of fresh weight reduction). The ALS gene sequencing of the eight silky windgrass populations, with cross-resistance to ALS inhibitors, revealed a point mutation at the Pro-197 position, causing amino acid substitution by Ser or Thr in the ALS enzyme. Overall, chlorsulfuron and clodinafop-propargyl were selecting agents of field-evolved multiple resistance to ALS- and ACCase-inhibiting herbicides in five silky windgrass populations. As the available postemergence-applied chemistries/modes of action registered for grass weed control in cereals are rather limited, adopting integrated management practices and implementing proactive and reactive measures to delay the evolution of resistant populations is essential.

Control of glyphosate-resistant (GR) junglerice is a challenging task in eastern Australia. There is limited information on the efficacy and reliability of alternate herbicides for GR populations of junglerice, especially when targeting large plants and when temperatures are high. A series of experiments were conducted to confirm the level of glyphosate resistance in three populations of junglerice and to evaluate the efficacy of alternate herbicides for the control of GR junglerice populations. The LD50 of glyphosate of B17/7, B17/34, and B17/35 populations was found to be 298, 2,260, and 1,715 g ae ha–1, respectively, suggesting that populations B17/34 and B17/35 were highly resistant to glyphosate. Glyphosate efficacy was reduced at high-temperature (35 C day/25 C night) compared with low-temperature conditions (25 C day/15 C night), suggesting that control of susceptible populations may also be reduced if glyphosate is sprayed under hot conditions. Preemergence herbicides dimethenamid-P (1,000 g ai ha–1) and pendimethalin (1,500 g ai ha–1) provided 100% control of GR populations (B17/34 and 17/35). Postemergence herbicides, such as clethodim (60 or 90 g ai ha–1), glufosinate (750 g ai ha–1), haloxyfop (52 or 78 g ai ha–1), and paraquat (400 or 600 g ai ha–1), applied at the four-leaf stage provided 100% control of GR populations. For larger junglerice plants (eight-leaf stage), postemergence applications of paraquat (400 or 600 g ai ha–1) provided greater weed control than clethodim, glufosinate, and haloxyfop. A mixture of either glufosinate or haloxyfop with glyphosate provided poor control of GR junglerice populations compared with application of glufosinate or haloxyfop applied alone. Efficacy of glufosinate and haloxyfop for the control of GR populations decreased when applied in the sequential spray after glyphosate application. This study identified alternative herbicide options for GR junglerice populations that can be used in herbicide rotation programs for sustainable weed management.

Owing to the lack of effective POST herbicide options, producers typically rely on nicosulfuron as the main POST grass herbicide in sweet corn production systems. In 2019, a Wisconsin sweet corn producer reported fall panicum control escapes after spraying nicosulfuron. Seeds from mature plants were collected to (1) measure fall panicum response to acetolactate synthase (ALS)-inhibiting herbicides, (2) elucidate the resistance mechanism, and (3) evaluate its response to alternative POST herbicides. Greenhouse and laboratory investigations were conducted to assess fall panicum response to ALS-inhibiting herbicides and elucidate the resistance mechanism. Dose–response results showed that fall panicum was highly resistant to nicosulfuron with a resistance ratio of >12.9-fold (survived rates >254 g ai ha−1, or 8× the field label rate). Molecular and genetic studies indicated that there are multiple ALS gene copies in fall panicum and that resistance was due to a mutation in one copy, resulting in an Asp-376-Glu amino acid substitution. Additional greenhouse experiments indicate that clethodim (105 g ai ha−1), quizalofop-p-ethyl (70 g ae ha−1), glyphosate (864 g ae ha−1), and glufosinate (650 g ai ha−1) are effective POST options to manage the ALS-resistant fall panicum (>90.0% control and 96.8% biomass reduction) in rotational years. The 4-hydroxyphenylpyruvate dioxygenase (HPPD)-inhibiting herbicides isoxaflutole (105 g ai ha−1), mesotrione (105 g ai ha−1), tembotrione (92 g ai ha−1), and tolpyralate (39 g ai ha−1) did not provide effective POST fall panicum control. Because these herbicides are commonly used for POST weed control in sweet corn, more investigations are required to evaluate combinations of HPPD-inhibiting herbicides with herbicides from other sites of action for POST fall panicum control. Herein we confirm the first case of herbicide resistance in fall panicum in the United States.

A field study was conducted twice in Elizabeth, MS, at on-farm sites in 2010–11 and 2011–12, and twice in 2012–13 at Mississippi State University’s Delta Research and Extension Center in Stoneville, MS, to evaluate glyphosate-resistant (GR) Italian ryegrass control and crop response to fall treatments followed by postemergence herbicide treatments in winter and/or spring. Italian ryegrass was controlled ≥92% and 61% following S-metolachlor and tillage 77 d after fall treatments (DA-FT), respectively. S-metolachlor fall treatment provided 33% greater control than clethodim winter treatment at 21 d after winter treatments (DA-WT). Tillage fall treatment followed by (fb) clethodim winter treatment fb paraquat spring treatment provided similar control (93%) to treatments containing S-metolachlor fall treatment fb a winter or spring herbicide treatment (≥93%) 24 d after spring treatments (DA-ST). Greatest soybean and corn density and yield were also observed following programs containing S-metolachlor fall treatment. Sequential postemergence herbicide treatments were not required to increase corn and soybean density and yield when S-metolachlor was used as a fall treatment. Growers have the best opportunity to maximize GR Italian ryegrass control when S-metolachlor fb a winter or spring herbicide treatment is used.

Junglerice is becoming more prevalent in Tennessee, Arkansas, and Mississippi row crop fields. The evolution of glyphosate-resistant (GR) junglerice populations is one reason for the increase. Another possible explanation is that glyphosate and clethodim grass activity is being antagonized by dicamba. This question has led to research to examine whether sequential applications alleviate antagonism observed with dicamba plus glyphosate and/or clethodim mixtures and determine whether sequential treatments with those herbicides at 24 h, 72 h, or 168 h can improve junglerice control. Glyphosate + clethodim applications provided >90% junglerice control. The observed levels of antagonism varied by whether the location of the test was in the greenhouse or the field, and the timing of applications. In the greenhouse, clethodim + dicamba provided excellent control, whereas in the field, the same treatment showed a greater than 30% reduction in junglerice control compared with clethodim alone. However, control was restored by using a mixture of glyphosate + clethodim without dicamba. The environment at the time of application and relative GR level of the junglerice influenced the overall control of these sequential applications. When clethodim applied first followed by dicamba at 72 h or 168 h, better control was observed compared with applying dicamba followed by clethodim. Overall, mixing glyphosate + clethodim provided the most complete junglerice control regardless of timing. These data confirm that leaving dicamba out of the spray tank will mitigate herbicide antagonism on junglerice control. These data would also indicate that avoiding dicamba and glyphosate mixtures will also improve the consistency of control with glyphosate-susceptible junglerice.

Junglerice has become a major weed in Tennessee cotton and soybean fields. Glyphosate has been relied on to control these accessions over the past two decades, but in recent years cotton and soybean producers have reported junglerice escapes after glyphosate + dicamba and/or clethodim applications. In the growing seasons of 2018 and 2019, a survey was conducted of weed escapes in dicamba-resistant (DR) crops. Junglerice was the most prevalent weed escape in these DR (Roundup Ready Xtend®) cotton and soybean fields in both years of the study. In 2018 and 2019, junglerice was found 76% and 64% of the time in DR cotton and soybean fields, respectively. Progeny from junglerice seeds collected during this survey was screened for glyphosate and clethodim resistance. Seventy percent of the junglerice accessions tested had an effective relative resistance factor to glyphosate of 3.1 to 8.5. In all, 13% of the junglerice accessions could no longer be effectively controlled with glyphosate. This research also showed that all sampled accessions could still be controlled with clethodim in a greenhouse environment, but less control was observed in the field. These data also suggest that another cause for the poor junglerice control is dicamba antagonism of glyphosate and clethodim activity.

Overreliance on herbicides for weed control has led to the evolution of herbicide-resistant Palmer amaranth populations. Farm managers should consider the long-term consequences of their short-term management decisions, especially when considering the soil weed seedbank. The objectives of this research were to (1) determine how soybean population and POST herbicide application timing affects in-season Palmer amaranth control and soybean yield, and (2) how those variables influence Palmer amaranth densities and cotton yields the following season. Soybeans were planted (19-cm row spacing) at a low-, medium-, and high-density population (268,000, 546,000, and 778,000 plants ha–1, respectively). Fomesafen and clethodim (280 and 210 g ai ha–1, respectively) were applied at the VE, V1, or V2 to V3 soybean growth stage. Nontreated plots were also included to assess the effect of soybean population alone. The following season, cotton was planted into these plots so as to understand the effects of soybean planting population on Palmer amaranth densities in the subsequent crop. When an herbicide application occurred at the V1 or V2 to V3 soybean stage, weed control in the high-density soybean population increased 17% to 23% compared to the low-density population. Economic return was not influenced by soybean population and was increased 72% to 94% with herbicide application compared to no treatment. In the subsequent cotton crop, Palmer amaranth densities were 24% to 39% lower 3 wk after planting when following soybean sprayed with herbicides compared to soybean without herbicides. Additionally, Palmer amaranth densities in cotton were 19% lower when soybean was treated at the VE stage compared to later stages. Thus, increasing soybean population can improve Palmer amaranth control without adversely affecting economic returns and can reduce future weed densities. Reducing the weed seedbank and selection pressure from herbicides are critical in mitigating resistance evolution.

With the spread of a new invasive plant species, it is vital to determine the effectiveness of removal strategies as well as their advantages and disadvantages before attempting widespread removal. While thousands of dollars have been spent to curtail the spread of wavyleaf basketgrass [Oplismenus undulatifolius (Ard.) P. Beauv.], a relatively new invasive species, the lack of a cohesive management plan and funding has made controlling this species especially difficult. We assessed the efficacy of a variety of chemical control methods and hand weeding for this species and followed select methods over time. We also assessed the potential for ecosystem recovery following removal by measuring total and native species richness in response to treatments. Our pilot study revealed a wide breadth of responses to our eight herbicides, with fluazifop plus fenoxaprop, imazapic, quizalofop, and sulfometuron methyl being the least effective. In our follow-up experiments, hand weeding, glyphosate, and clethodim treatments were effective at reducing O. undulatifolius percent cover, density, and biomass, with an average reduction of at least 48% in the first year. However, we found substantial variation in the effectiveness of clethodim between our two experiments, which was likely driven by site differences. We also found that all three of these removal methods were effective at reducing the number of O. undulatifolius flowering stems and the height of those stems, which will likely reduce the spread of this species to new areas. Finally, we found that these methods have the potential to restore total and native species richness, but that glyphosate-treated plots did not fully recover until 2 yr after treatment.

Proper management of glufosinate in glufosinate-resistant crop technologies is needed to mitigate the likelihood of resistance evolution. Antagonism may result from mixtures of glufosinate and other commonly used POST herbicides in soybean and cotton. Two experiments were conducted at the Arkansas Agricultural Research and Extension Center in Fayetteville, AR, in 2015 and 2016 to evaluate mixtures of glufosinate + clethodim and glufosinate + glyphosate on barnyardgrass, broadleaf signalgrass, johnsongrass, and large crabgrass. Furthermore, droplet spectra analyses were conducted to determine if droplet size was associated with identification of herbicide interactions. Antagonism was dependent on the herbicide rates and the weed species. For barnyardgrass and large crabgrass control 4 wk after treatment, glufosinate + glyphosate was antagonistic at all rates evaluated. When large crabgrass was evaluated, some mixtures (e.g., 595 g ha–1 glufosinate + 76 g ha–1 clethodim) had a significant reduction in control relative to one of the herbicides applied alone. Glufosinate (451 and 595 g ai ha–1) + glyphosate (867 and 1,735 g ae ha–1) was antagonistic at all four possible rate combinations for broadleaf signalgrass control. Fewer instances of antagonism were observed for seedling johnsongrass control than for other species, but certain treatments were identified as antagonistic (e.g., glufosinate at 451 g ai ha–1 + clethodim at 76 g ai ha–1). Overall, antagonism was less likely and greater control was observed when the highest rates of both herbicides in a given mixture were used. The addition of glyphosate or clethodim to glufosinate can increase the volume median diameter and decrease the percentage volume of fines, compared to glufosinate alone. The droplet spectra analyses indicate that the glufosinate performance may be negatively affected by the addition of glyphosate or clethodim.

Giant miscanthus has the potential to move beyond cultivated fields and invade noncrop areas, but this can be overshadowed by aesthetic appeal and monetary value as a biofuel crop. Most research on giant miscanthus has focused on herbicide tolerance for establishment and production rather than terminating an existing stand. This study was conducted to evaluate herbicide options for control or terminating a stand of giant miscanthus. In 2013 and 2014, field experiments were conducted on established stands of the giant miscanthus cultivars ‘Nagara’ and ‘Freedom.’ Herbicides evaluated in both years included glyphosate, hexazinone, imazapic, imazapyr, clethodim, fluazifop, and glyphosate plus fluazifop. All treatments were applied in summer (June or July) and September. For both years, biomass reduction ranged from 85% to 100% when glyphosate was applied in June or July at 4.5 or 7.3 kg ae ha−1. No other treatment applied at this timing provided more than 50% giant miscanthus biomass reduction 1 yr after application. September applications of glyphosate were not consistent: treatments in 2013 reduced biomass by 40% or less, whereas in 2014, at all rates provided at least 78% biomass reduction. Glyphosate applied in June or July was the only treatment that provided effective and consistent control of giant miscanthus 1 yr after treatment.

In Argentina, Lolium spp. occur in 40% of winter cereal crops from the Pampas. Several years ago, cases of glyphosate-resistant perennial ryegrass (Lolium perenne L.) were detected, and the use of acetyl-CoA carboxylase (ACCase)-inhibiting herbicides to eradicate these plants has been considered. The aim of this study was to evaluate the sensitivity of a putative pinoxaden-resistant L. perenne population to ACCase-inhibiting herbicides. Around 80% of plants from the putative resistant population survived at a recommended dose of pinoxaden, and they produced viable seeds. The resistance indices (RIs) to pinoxaden were 5.1 and 2.8 for plant survival and seed production, respectively. A single point mutation that conferred a Asp-2078-Gly substitution in ACCase was the source of the resistance. To match the plant control achieved in the susceptible population, the resistant population required 5.4- and 10.4-fold greater doses of clethodim and quizalofop, respectively. RIs for viable seed production when treated with clethodim and quizalofop were 3.3 and 6.6, respectively. The Asp-2078-Gly mutation endowed significant levels of resistance to pinoxaden, clethodim, and quizalofop. For three herbicides, the level of resistance of a pinoxaden-resistant L. perenne population to ACCase inhibitors was evaluated, based on an evaluation of dose response for plant survival and seed production. The RIs were higher for plant survival than for seed production. In Argentina, the selection pressure associated with clethodim and haloxifop preplant application and pinoxaden use on wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.) crops, would have favored the propagation of the Asp-2078-Gly mutation with its associated resistance.

Management of volunteer glyphosate-resistant (GR) corn may be problematic in soybean resistant to glyphosate and 2,4-D or dicamba, as auxinic herbicides often antagonize graminicide efficacy. Field and greenhouse trials were conducted using mixtures of 2,4-D or dicamba in combination with glyphosate and clethodim-A (formulated without an adjuvant) or clethodim-SM (adjuvant-inclusive formulation) to determine the effect on volunteer GR corn control. Neither auxinic herbicide reduced clethodim efficacy, regardless of clethodim rate or formulation in field trials. However, the addition of glyphosate to these mixtures at the 35 g ai ha−1 clethodim dose reduced control from clethodim-A and clethodim-SM by 62% to 75% and 27% to 47%, respectively. Increasing the clethodim dose to 105 g ha−1 or greater in combination with glyphosate and either auxinic herbicide generally restored clethodim efficacy (74% to 98% control); in one site-year, the addition of glyphosate plus dicamba to clethodim-A at 140 g ha−1 still reduced control by 34%. In greenhouse experiments, clethodim-A efficacy was reduced by 17% and 28% when applied with glyphosate plus 420 and 1,680 g ae ha−1 2,4-D, respectively, in the absence of crop oil concentrate (COC). Increasing the dose of dicamba in a similar mixture had a negligible effect. Irrespective of auxinic herbicide dose, the inclusion of COC to clethodim-A mixtures with glyphosate plus 2,4-D or dicamba resulted in ≥ 90% control. These results specify an enhanced risk of reduced clethodim efficacy on volunteer GR corn when glyphosate is added to mixtures containing 2,4-D or dicamba. To optimize control from these mixtures, clethodim should be applied at ≥ 105 g ha−1 and should include an activator adjuvant in the form of COC and/or an adjuvant-inclusive clethodim formulation. This recommendation contrasts with several labels of clethodim that do not require COC when applied with adjuvant-loaded glyphosate products.

Nonnative annual brome invasion is a major problem in many ecosystems throughout the semiarid Intermountain West, decreasing production and biodiversity. Herbicides are the most widely used control technique but can have negative effects on co-occurring species. Graminicides, or grass-specific herbicides, may be able to control annual bromes without harming forbs and shrubs in restoration settings, but limited studies have addressed this potential. This study focused on evaluating the efficacy of glyphosate and four graminicides to control annual bromes, specifically downy brome and Japanese brome. In a greenhouse, glyphosate and four graminicides (clethodim, sethoxydim, fluazifop-P-butyl, and quizalofop-P-ethyl) were applied at two rates to downy brome plants of different heights (Experiment 1) and to three accessions of downy brome and Japanese brome of one height (Experiment 2). All herbicides reduced downy brome biomass, with most effective control on plants of less than 11 cm and with less than 12 leaves. Overall, quizalofop-P-ethyl and fluazifop-P-butyl treatments were most effective, and glyphosate and sethoxydim treatments least effective. Accessions demonstrated variable response to herbicides: the downy brome accession from the undisturbed site was more susceptible to herbicides than downy brome from the disturbed accession and Japanese brome accessions. These results demonstrate the potential for graminicides to target these annual bromes in ecosystems where they are growing intermixed with desired forbs and shrubs.

The use of cover crops in soybean production systems has increased in recent years. There are many questions surrounding cover crops—specifically about benefits to crop production and most effective herbicides for spring termination. No studies evaluating cover crop termination have been conducted across a wide geographic area, to our knowledge. Therefore, field experiments were conducted in 2016 and 2017 in Arkansas, Indiana, Mississippi, Missouri, and Wisconsin for spring termination of regionally specific cover crops. Glyphosate-, glufosinate-, and paraquat-containing treatments were applied between April 15 and April 29 in 2016 and April 10 and April 20 in 2017. Visible control of cover crops was determined 28 days after treatment. Glyphosate-containing herbicide treatments were more effective than paraquat- and glufosinate-containing treatments, providing 71% to 97% control across all site years. Specifically, glyphosate at 1.12 kg ha−1 applied alone or with 2,4-D at 0.56 kg ha−1, saflufenacil at 0.025 kg ha−1, or clethodim at 0.56 kg ha−1 provided the most effective control on all grass cover crop species. Glyphosate-, paraquat-, or glufosinate-containing treatments were generally most effective on broadleaf cover crop species when applied with 2,4-D or dicamba. Results from this research indicate that proper herbicide selection is crucial to successfully terminate cover crops in the spring.