Palmer amaranth, a competitive weed in cotton and soybeans, poses challenges due to its rapid growth, high fertility, and herbicide resistance. Effective management strategies targeting sex ratios could reduce seed production by female plants. Protoporphyrinogen oxidase (PPO-) inhibiting herbicides play a role in the evolving resistance of Amaranthus spp. in the Midwestern US. These herbicides may also affect the male-to-female ratio of Palmer amaranth. A two-year field experiment (2015 and 2016) was conducted in a soybean field in Collinsville, Illinois, evaluating various preemergence and postemergence PPO-inhibiting herbicide treatments. Untreated Palmer amaranth populations exhibited a bias towards females. Pre-emergence application of sulfentrazone and flumioxazin effectively reduced Palmer amaranth density (1.66 plants m-2) throughout the season, while post-emergence applications of fomesafen and lactofen provided limited control (27 and 31 plants m-2). Early-season mortality was high (96 %) among Palmer amaranth seedlings, especially with pyroxasulfone+fluthiacet-methyl treatment. Fomesafen increased female biomass (28.8 %) while reducing male biomass compared to non-treated control. In 2015, pyroxasulfone+fluthiacet-methyl and acetochlor altered the male-to-female sex ratio compared to the non-treated control, with pyroxasulfone+fluthiacet-methyl reducing the proportion of females (-0.11 M:F) and acetochlor slightly increasing the proportion of males (0.03 M:F), though not different from a 1:1 ratio. In 2016, pendimethalin and flumioxazin-2 resulted in a strong female-biased sex ratio, with an almost exclusively female population. In both years, the non-treated control plots (-0.58 and -0.55 M:F) maintained a naturally female-biased sex ratio, deviating significantly from a 1:1 ratio. These findings suggest that specific herbicide treatments can alter the sex ratio.. Understanding sex determination in Palmer amaranth holds promise for developing more effective control strategies in the future.

Recently a premix of tolpyralate and bromoxynil was registered in the USA and Canada by Corteva Agriscience for weed control in cereals. Limited information exists on weed control efficacy and crop safety with this new herbicide pre-mixture. Greenhouse trials were conducted for two years to test the efficacy of tolpyralate and bromoxynil combinations on 14 broadleaf and 4 grass weeds and crop safety in wheat and barley. Four combinations of tolpyralate and bromoxynil at 1:10 ratio (3.75 + 37.5, 7.5+ 75, 11.25 + 112.5, and 15 + 150 g ai ha-1) as a tank-mix and premix were tested. Stand-alone treatments of tolpyralate and bromoxynil were also included in this study. The lowest tested rate of tolpyralate (3.75 g ha-1) provided 10 to 98% and 27 to 77% control of broadleaf and grass weeds, respectively. Bromoxynil at the lowest tested rate (37.5 g ha-1) provided 16 to 80% and 0 to 30% control of broadleaf and grass weeds, respectively. Tank-mixing these two herbicides at the same rates had improved broadleaf (60 to 100%) and grass (45 to 94%) weed control. The minimum recommended field use rate of tolpyralate +bromoxynil (15 + 150 g ha-1) controlled all the broadleaf weeds >95%. This combination also controlled green foxtail, barnyardgrass and large crabgrass >90%. Additive or synergistic effect between the two herbicides was observed on several broadleaf and grass weed species. Among all the tested weeds, greater synergistic effect was observed on kochia, chickweed, wild mustard, corn poppy, barnyardgrass, green foxtail, and fall panicum. The premix of the two herbicides provided similar broadleaf control, but better grass weed control compared to the tank-mix combinations. Premix was safe on wheat and barley.

Clethodim is an important herbicide for managing Texas panicum. However, its efficacy is influenced by the weed size and environmental stress during application. Therefore, field and greenhouse studies were conducted in 2023 and 2024 to evaluate clethodim efficacy on various Texas panicum sizes. Clethodim was applied at Texas panicum sizes ranging from 5 cm to 60 cm. A sequential application was applied two weeks after the initial treatment for larger weed sizes (15 to 60 cm). In separate field and greenhouse studies, non-ionic surfactant (NIS), crop oil concentrate (COC), methylated seed oil (MSO), COC + ammonium sulfate (AMS), and MSO + AMS adjuvants were mixed with clethodim to determine efficacy on 10-15 cm and 20-30 cm Texas panicum. In the weed size study, sequential applications of clethodim increased Texas panicum control compared to a single application. At the 10-15 cm growth stage, a single application provided 90% Texas panicum control, whereas the sequential treatment improved control from 76% to 91% at the 15-20 cm growth stage. However, clethodim efficacy declined as Texas panicum size increased across single and sequential treatments. In the adjuvant studies, clethodim plus COC, COC+AMS, or MSO+AMS provided 91%, 93%, and 90% control at the 10-15 cm growth stage, respectively; however, efficacy decreased for 20-30 cm Texas panicum. Texas panicum efficacy was higher for clethodim plus MSO+AMS than clethodim plus MSO; however, AMS did not increase clethodim + COC efficacy. Overall, Texas panicum control with clethodim was most effective when weed height was 15 cm or less. A sequential application of clethodim was required for larger Texas panicum (>15 cm). Clethodim plus COC or MSO+AMS provided the highest control of Texas panicum. This study demonstrated that successful Texas panicum management depends on applying clethodim at the optimum size and selecting the appropriate oil-based adjuvant especially at larger Texas panicum sizes.

Purple witch-weed is a parasitic plant that significantly impacts sorghum yields in semi-arid regions. It also affects crops like corn, millets, and rice. Developing purple witch-weed-resistant sorghum varieties is essential for integrated purple witch-weed management. This study evaluated the response of 48 sorghum genotypes to purple witch-weed under both pot and field conditions. Resistant varieties (Berhan and Framida) and susceptible varieties (Assosa-1, Adukara, and/or ETSL102967) were used as controls. The findings revealed substantial variability among the sorghum landraces in their response to purple witch-weed. Early maturing genotypes exhibited lower purple witch-weed densities, while late maturing ones were more susceptible. Notably, the ETSL102969 landrace showed strong resistance, comparable to the resistant variety Berhan. Additionally, the ETSL102970 landrace demonstrated superior resistance compared to Framida. Based on these results, ETSL102969 and ETSL102970 are recommended as valuable sources of resistance for breeding programs aimed at improving sorghum resistance against purple witch-weed in Ethiopia.

Auxinic herbicides are the second most used in Brazil, often combined with glyphosate in pre-plant burndowns management. However, their efficacy against Benghal dayflower at advanced growth stages remains poorly understood. Two field experiments were conducted in 2021 and 2022 on no-till fields naturally infested with Benghal dayflower at an advanced growth stage (∼50 cm height, 100% soil coverage) to evaluated the control efficacy of 2,4-D at 966 g ae ha-1, triclopyr at 720 g ae ha-1, fluroxypyr at 400 g ae ha-1 and dicamba at 720 g ae ha-1, combined or not with glyphosate (1,550 g ae ha-1). Dicamba was also tested at rates from 288 to 1,008 g ae ha⁻¹. Results indicate Benghal dayflower exhibits variable responses to auxin herbicides, influenced by both chemical family and the herbicide molecule. None of the treatments provided complete control at 8 wk after application (WAA). The highest visible control (∼77%) and dry mass reduction (∼57%) were provided by triclopyr (isolated or combined with glyphosate) and 2,4-D (combined with glyphosate), followed by fluroxypyr (isolated or combined with glyphosate) and 2,4-D (isolated), providing ∼69% visible control and 54% dry mass reduction. Even when statistical differences were detected by adding glyphosate to auxin herbicides, these differences were not sufficient to characterize a synergistic effect or improve control consistency. Dicamba (isolated or combined with glyphosate) provided the lowest control (∼54%) and dry mass reduction (∼30%). Additionally, dicamba doses up to 1008 g ae ha⁻¹ did not provide complete control (∼60% visible control and 51% dry mass reduction), suggesting that dicamba limitations cannot be mitigated through dose increase. By highlighting the challenges in controlling Benghal dayflower at advanced growth stages, these results emphasize the importance of early-stage weed control and the need to carefully assess which auxin herbicides to use and when glyphosate mixtures are necessary.

The knowledge of the critical periods of crop-weed competition is crucial for designing weed management strategies in cropping systems. In the Lower Yangtze Valley, China, field experiments were conducted in 2011 and 2012 to study the effect of interference from mixed natural weed populations on cotton growth and yield and determine the critical period for weed control (CPWC) in direct-seeded cotton. Two treatments were applied: allowing weeds to infest the crop or keeping plots weed-free for increasing periods (0, 1, 2, 4, 6, 8, 10, 12, 14, and 20 weeks) after crop emergence. The results showed that mixed natural weed infestations led to 35 to 55 cm shorter cotton plants with stem diameters 10 to 13 mm smaller throughout the season, fitting well with modified Gompertz and logistic models, respectively. Season-long competition with weeds reduced the number of fruit branches per plant by 65% to 82%, decreasing boll number per plant by 86% to 96% and single boll weight by approximately 24%. Weed-free seed cotton yields ranged from 2,900 to 3,130 kg ha-1, while yield loss increased with the duration of weed infestation, reaching up to 83% to 96% compared with permanent weed-free plots. Modified Gompertz and logistic models were used to analyze the impact of increasing weed control duration and weed interference on relative seed cotton yield (percentage of season-long weed-free cotton), respectively. Based on a 5% yield-loss threshold, the CPWC was found to be from 145 growing degree days (GDD) to 994 GDD, corresponding to 14 days after emergence (DAE) to 85 DAE. These findings emphasize the importance of implementing effective weed control measures from 14 DAE to 85 DAE in the Lower Yangtze Valley, China, to prevent crop losses exceeding a 5% yield-loss threshold.

Wild oat is a significant weed of cropping systems in the Canadian Prairies. Wild oat resistance to herbicides has increased interest in non-chemical management strategies. Harvest weed seed control techniques such as impact mills or chaff collection have been of interest in Prairie crops, with wild oat identified as a key target. To evaluate impacts of crop rotation maturity, harvest management and harvest weed seed control on wild oat, a study was conducted from 2016-2018 at four locations in the Canadian Prairies. Two-year crop rotations with either early, normal, or late-maturity crops were implemented before barley was seeded across all rotations in the final year. In addition, a second factor of harvest management (swathing or straight cut) was included in the study. Chaff collection was used in this study in an attempt to quantify wild oat seeds that were targetable by harvest weed seed control techniques. The hypothesis was that earlier maturing crops would result in increased wild oat capture at harvest and, therefore, lower wild oat populations. Wild oat density and wild oat biomass were lowest in the early maturing rotations. In addition, wild oat biomass was lower in swathed crops than in straight-cut crops. Wild oat seedbank levels reflected a similar trend with the lowest densities in early maturing rotation, then the normal maturity rotation and the late maturing rotation had the highest seedbank densities. Wild oat densities increased in all crop rotations; however, only harvest weed seed control and crop rotation were implemented as control measures. Wild oat numbers in the chaff were not reflective of the earliness of harvest. Crop yields suggest that competitive winter wheat stands contributed to the success of the early maturing rotations compared to other treatments. Early maturing rotations resulted in reduced wild oat populations, likely through a combination of crop competitiveness and rotational diversity, and harvest weed seed control impact in earlier maturing crops.

Fall-planted cover crops are becoming popular among growers in the Midwest for various reasons, including weed suppression. Cereal rye is the most planted cover crop in Nebraska. Glyphosate availability was limited in 2022, so growers sought information about glyphosate alternatives for terminating cover crops, such as cereal rye. The objectives of this study were to evaluate alternative acetyl coA carboxylase (ACCase)-inhibiting herbicides for terminating cereal rye 15 days before soybean planting (DBSP), at soybean planting day (SPD), and 15 days after soybean planting (DASP) and their effect on weed control, density, biomass, soybean plant stand, and grain yield. Field experiments were conducted from 2018 to 2020 in southcentral Nebraska. Cereal rye biomass collected 15 days after termination was 394, 1,697, and 3,700 kg ha−1 in 2019 and 330, 1,304, and 4,550 kg ha−1 in 2020, respectively, for 15 DBSP at SPD and 15 DASP termination timings. Clethodim provided 77% control of cereal rye 15 DBSP compared with greater than 94% control with fluazifop-P-butyl, fluazifop-P-butyl/fenoxaprop-P-ethyl, quizalofop-P-ethyl, and glyphosate. Similarly, at SPD and 15 DASP termination timings, clethodim resulted in 66% and 31% control of cereal rye, respectively, compared to greater than 92% control with other ACCase-inhibitors and glyphosate. Palmer amaranth control at R5 soybean growth stage was 70%, 88%, and 96%, respectively, at 15 DBSP, SPD, and 15 DASP termination timing. Soybean yield was reduced to 2,184 kg ha−1 when cereal rye was terminated at 15 DASP compared to 4,566 kg ha−1 when terminated at SPD and 4,460 kg ha−1 with 15 DBSP.

Galium aparine L. var. echinospermum (Wallr.) Cuf., an annual or winter annual broadleaf weed in the Rubiaceae family, has become troublesome due to its herbicide resistance in the wheat fields of the Huang-Huai-Hai region in China. Four cleavers populations (JS-15, SD-10, JS-22, and AH-20) were collected from the wheat fields of Jiangsu, Shandong, and Anhui Province, where florasulam control was absent. This study identified the herbicide resistance patterns and investigated the mechanism underlying the florasulam resistance. The whole-plant dose-response experiments revealed a notable variation in the degree of resistance exhibited by three specific populations towards florasulam, in comparison to the most sensitive populations (S and AH-9), with the highest resistance index reaching 841.4. Acetolactate Synthase gene-sequencing assay found that R plants from JS-15, JS-22, and AH-20 had a Trp-574-Leu mutation, while no known ALS resistance mutations were discovered in SD-10 plants. In vitro ALS enzyme activity assays also indicated that the extractable ALS from the resistant plants of JS-15, JS-22, and AH-20 was greatly resistant to florasulam relative to that of the susceptible. Additionally, according to the resistance rating system, all resistant populations were susceptible to Carfentrazone-ethyl + MCPA-Na and Bipyrazone + Fluroxypyr-methyl. AH-20, JS-15, and JS-22 exhibited resistance to selected ALS, 4-hydroxyphenylpyruvate dioxygenase, and photosystem Ⅱ complex inhibitors, demonstrating RR and RRR resistance profiles, whereas AH-9 displayed S-sensitivity to virtually all tested agents. SD-10, on the other hand, showed RR and RRR resistance to HPPD and PSII inhibitors, but exhibited S-sensitivity specifically to tribenuron-methyl. These findings indicate that a target site-based mechanism drives the resistance to the ALS inhibitor florasulam in cleavers populations, but NTSR resistance may have also contributed (was not investigated). Other herbicides with different sites of action were tested and were active against cleavers.

Site-specific herbicide applications with remotely piloted aerial application systems (RPAASs) offer the potential for reducing herbicide inputs in turfgrass systems. However, information on spray nozzle selection and application volume for this approach is lacking. The objective of this study was to evaluate the effects of nozzle type and spray volume on the efficacy of site-specific herbicide application in turf using an RPAAS, focusing on large crabgrass control with quinclorac. The research was conducted in 2022 at two College Station, TX sites. The treatments were combinations of three nozzle types [XR 80-015 (conventional, extended range), DG 80-015 (drift guard), and AI 80-015 (air induction) flat fan nozzles] and two spray volumes [10 and 15 L ha-1], applied with a single-nozzle RPAAS. A spray volume of 102 L ha-1 applied with a CO2 pressurized 4-nozzle boom backpack sprayer served as a check for comparison. Two additional treatments were also included: a pure formulated herbicide application (without dilution in water) using an RPAAS equipped with an XR 80-005 flat fan nozzle at 4.6 L ha-1 and an untreated control. The backpack sprayer application resulted in the highest spray solution deposits on large crabgrass plants (12 times more on average), compared to the RPAAS applications. Nevertheless, applications using the RPAAS with the DG and AI nozzles at 10 or 15 L ha-1 provided similar levels of weed control as that of the backpack sprayer at 102 L ha-1, indicating that RPAAS can be effectively used for site-specific herbicide applications in turf. This study also suggests that large crabgrass can be controlled using RPAAS with a range of spray nozzle types at low application volumes in turfgrass. Further research is needed to assess the efficacy of RPAAS-based herbicide applications across a range of herbicides, weed species, and environmental conditions.

Uncontrolled weeds can cause billions of dollars in yield loss in corn and soybean production fields in the United States. Growers often use herbicides to control weeds to avoid yield loss. The objective of this study was to estimate the cost of herbicides used in corn and soybean production in the United States. On-farm herbicide usage data were extracted from corn (2021) and soybean (2023) surveys of the United States Department of Agriculture–National Agricultural Statistics Service (USDA-NASS 2022a, 2024a) Agricultural Chemical Use Program. Commonly used or known products were assumed for each reported herbicide. Based on the USDA-NASS surveys, approximately 107.8 and 89.1 million kg of herbicides were applied in corn and soybean production in 2021 and 2023, respectively, in the United States. Glyphosate (33.8 million kg; in various salt forms), atrazine (26.8 million kg), and mesotrione (2.4 million kg) were the most widely applied herbicides, on 79%, 65%, and 47% of corn, respectively, planted in 2021 (USDA-NASS 2022b). Similarly, glyphosate (in various salt forms) was the most widely applied herbicide in soybean, followed by 2,4-D (15.9 million kg; in various salt forms) and glufosinate-ammonium (4.4 million kg), which were applied to 58% and 23% of soybean, respectively, planted in 2023 (USDA-NASS 2024c). Using the average retail price of herbicide products from Kansas State University, University of Nebraska−Lincoln, and North Dakota State University publications, herbicides (excluding adjuvants and application costs) would have cost approximately $3.2 and $4.1 billion in corn and soybean in 2021 and 2023, respectively.

Branched broomrape management is of increasing concern to California processing tomato growers. Field research was conducted in 2023 and 2024 to evaluate various application timings of chemigated rimsulfuron alone, preplant incorporated (PPI) sulfosulfuron paired with chemigated rimsulfuron, as well as foliar maleic hydrazide alone and paired with PPI sulfosulfuron and chemigated rimsulfuron. In 2023, all treatments with 70 g ai ha-1 rimsulfuron, alone or paired with PPI sulfosulfuron, reduced broomrape emergence 77 to 92% compared to the nontreated control. In 2024, broomrape pressure was higher, and all rimsulfuron treatments reduced broomrape emergence 68 to 86% compared to the control. In both years, five applications of foliar maleic hydrazide reduced broomrape emergence through at least midseason. The 2024 experiment included a combination treatment of PPI sulfosulfuron, chemigated rimsulfuron, and foliar maleic hydrazide, which resulted in fewer than four broomrape clusters per plot. In a 2024 grower-scale demonstration trial, two application regimes totaling 70 g ai ha-1 of chemigated rimsulfuron reduced broomrape emergence 83 to 89% compared to the control. Overall, chemigated rimsulfuron applied at various timings and rates totaling 70 g ai ha-1 reduced broomrape emergence by two-thirds or more compared to the nontreated plots. No crop injury was observed in trials with rimsulfuron, sulfosulfuron, or maleic hydrazide treatments in small plot trials or with rimsulfuron in the grower-scale demonstration trial. Under a recently approved 24(c) Special Local Need label, California growers can use three applications of rimsulfuron applied via chemigation to suppress broomrape in known infested fields or to reduce the risk of broomrape establishment in fields of concern for this quarantine pest. Promising results from sulfosulfuron and maleic hydrazide suggest that registering additional herbicides could help develop even more robust branched broomrape management programs.

Weeds incur up to AUD $4 billion in economic loss annually to Australian agriculture. Despite this knowledge, there are few quantitative data on yield loss and control costs caused by weeds to the industry. Reported herein is the economic cost of managing the emerging, invasive Navua sedge weed to the grazing and cropping (sugarcane) industries of northern Queensland, Australia, following its introduction into the region in the 1970’s. Between 2020-2022, through a survey questionnaire given to impacted stakeholders (farmers), information relating to control cost, yield loss, and infestation history were documented. Collated data were analyzed using mainly non-parametric statistics due to the skewed and/or qualitative nature of many of the responses. Invasion history of the weed on farming properties is relatively recent (time: 10-20 yrs), and infestation level, though majorly and currently of low-medium status (median value: 22.5%), varies appreciably amongst properties. Median cost of managing Navua sedge was AU $72.91/hectare (AU $82.06 present value). This cost nor the type of management tactics (chemical vs. integrated weed management [IWM]) did not vary between land use types; however, the labor (relative to chemical and machinery) component of the control cost was the greatest. The currently approved herbicide, halosulfuron-methyl (SempraTM), is largely ineffective in controlling the weed due to its inability to deplete below-ground tubers of the weed. Correlation analyses suggest control costs will continue to increase with increasing Navua sedge infestation over time, especially in grazing lands. Farmers show high awareness of the challenge of managing the new weed incursion. Farmers are using myriads of strategies, including willingness to impose strict biosecurity measures and IWM tactics while waiting for more effective herbicides and promising biocontrol agents to minimize the spread and impact of the weed.

Indaziflam was evaluated in Connecticut and Tennessee, USA, for weed control and safety of container-grown ornamental plants. Indaziflam was applied at 49, 98, or 196 g ha-1 to container-grown ornamental plants on an outdoor gravel pad and preemergence or early postemergence to weeds in greenhouse. Ornamental plants were treated twice annually in 2020 and 2021 in Connecticut, and in 2019 and 2020 in Tennessee, with approximately six weeks between applications. Chinese pyramid juniper, common juniper, eastern hemlock, eastern white pine, and Norway spruce in Connecticut, USA, and 'Andorra Compacta’ creeping juniper and 'Black Dragon’ Japanese cedar, ‘Blue Rug’ creeping juniper, and ‘Blue Pfitzer’ Chinese pyramid juniper in Tennessee, USA, were not injured with indaziflam regardless of rate applied. Preemergence application of indaziflam reduced densities of creeping woodsorrel, hairy bittercress, giant foxtail, and large crabgrass 72 to 100%, depending upon the indaziflam rate applied, by 28 d after treatment (DAT). When applied early postemergence, indaziflam provided 97 to 99% control of creeping woodsorrel (1- to 2-leaf), fringed willowherb (4- to 6-leaf), hairy bittercress (cotyledon to 1-leaf), and mouse-ear chickweed (2- to 4-leaf) by 28 DAT. Compared with the nontreated control, the total fresh shoot biomass reduction was 86 to 100% and 78 to 100% following preemergence or postemergence applications. Indaziflam offers a new site-of-action with excellent safety and weed control in the tested ornamental plants.

Narrow row spacing and layered residual herbicides are recommended for season-long control of herbicide-resistant weeds, but limited research is available to describe interactions between the two practices. The integration of narrow row spacing with layered residual herbicides in herbicide-resistant soybean was evaluated in four site-years. A split-split plot treatment arrangement where the whole plot was soybean trait (LLGT27 or EnlistE3), the subplot was row spacing (38 or 76 cm), and the sub-subplot factor was herbicide program with five treatments: nontreated, preemergence herbicide only (PRE), PRE followed by postemergence (PRE fb POST), PRE fb POST with overlapping residual herbicide (POR), and weed free. Weed control was evaluated through R7 soybean, and weed biomass was collected before POST applications and at R7 soybean. Soybean yield was recorded. Data were subjected to analysis of variance and means separation (α = 0.05). Row spacing had minimal effects on weed control and mixed effects on yield. Waterhemp and Venice mallow control ranged from 83% to 100% 4 weeks after treatment (WAT). POST and POR treatments provided ≥ 94% control of Palmer amaranth 4 WAT; however, PRE resulted in 33% Palmer amaranth control. All treatments resulted in ≥ 95% Palmer amaranth and yellow foxtail control at Scandia during 2021. The greatest income in rainfed site-years was Enlist soybean planted in 76-cm rows with PRE herbicide treatment. The greatest income in the irrigated site-year was with Enlist soybean planted in 38-cm rows with PRE herbicide treatment. Both POST and POR increase weed control compared to PRE, regardless of row spacing in the soybean varieties evaluated, although POR resulted in less income than POST treatments. However, this research did not evaluate weed seed production, which is crucial for long-term weed management and profitability.

Pearl millet is a climate-resilient grain and forage crop. Weeds pose a major constraint to its successful production. Limited herbicide options for grass weed control in pearl millet is a serious problem. The objectives of this study were to 1) evaluate the sensitivity of pearl millet parental lines to POST-applied clethodim (136 g ai ha-1), quizalofop-p-ethyl (QPE) (77 ai g ha-1), imazamox (52 g ai ha-1) and nicosulfuron (70 g ai ha-1), and 2) characterize the sensitivity of selected lines to imazamox and nicosulfuron. A total of 56 parental lines were tested. Three lines with low sensitivity to imazamox (ARCH35R, 45R, and 73R), two to nicosulfuron (ARCH45R and 73R), one line with high sensitivity (ARCH21B), and a susceptible sorghum (SOR) hybrid (P84G62) to both herbicides were characterized. All parental lines were sensitive to clethodim and QPE (only four lines showed 2 to 12% survival with 90 to 95% injury at 21 d after application [DAA]). However, all parental lines showed variable sensitivity to imazamox and nicosulfuron (70 to 100% survival with 5 to 70% visible injury and shoot dry biomass reduction at 21 DAA). Dose-response assays revealed that ARCH35R, 45R, and 49R had 7.7 to 12.2 and 3.2- to 12.2-fold reduced sensitivity to imazamox compared to the ARCH21B and SOR, respectively. Similarly, ARCH45R and 49R had 2.5 to 6.0 and 1.5- to 3.7-fold reduced sensitivity to nicosulfuron compared to ARCH21B and SOR, respectively. These findings confirm the first report of reduced sensitivity to imazamox and nicosulfuron among pearl millet lines, suggesting their potential use for in-season grass weed control.

A limited number of herbicides and sites of action are registered for use in sugarcane in Louisiana. Repeated use of the same sites of action can lead to the evolution of herbicide resistance in weeds. Therefore, it is critical to evaluate additional sites of action to provide growers with options for rotating herbicides to reduce the risk of resistance. Topramezone, indaziflam, and a formulation including mesotrione, bicyclopyrone, atrazine, and S-metolachlor, along with more common herbicide applications (pendimethalin, and metribuzin, clomazone, and diuron), were evaluated in the spring for injury to sugarcane, weed control, sugarcane yield, and sugar yield. Of these treatments, clomazone applied with diuron was the only herbicide combination to consistently injure the crop, with injury estimates ranging from 11 to 36%, which frequently resulted in reduced sugar yield with losses between 2.3% to 24.1% of the non-treated control. In most treatments, an increase in itchgrass counts was observed between harvests, indicating that additional control strategies will be needed in fields infested with this weed. However, topramezone alone and with triclopyr was well tolerated by sugarcane, with injuries ranging from 0 to 11% two weeks after treatment. Indaziflam and combined application of mesotrione, bicyclopyrone, atrazine, and S-metolachlor injury was at or under 10% two weeks after treatment. The tolerance of sugarcane for these herbicides suggests that they can be incorporated into weed management strategies in sugarcane. These herbicides would increase the sites of action available to be applied in sugarcane and help mitigate the risk of herbicide-resistant weeds.

Tetflupyrolimet is the first herbicide with a novel site of action to be commercialized for use in agronomic crops in three decades. Direct-seed rice field experiments were conducted at research facilities near Stuttgart (silt loam), AR, and Keiser (clay), AR, to evaluate tetflupyrolimet as a preemergence herbicide versus commercial standards. Greenhouse experiments determined the influence of soil moisture on pre- and postemergence (POST) barnyardgrass control with tetflupyrolimet and clomazone, and the impact of a delayed flood on efficacy when POST-applied. For the field experiments, clomazone, tetflupyrolimet, and quinclorac were applied individually PRE at 336 and 560, 134 and 224, and 336 and 560 g ai ha-1, respectively, on a silt loam and clay soil, along with clomazone plus tetflupyrolimet and clomazone plus quinclorac at the same rates. The soil moisture experiment included a single PRE and POST application of clomazone at 336 g ai ha-1, tetflupyrolimet at 134 g ai ha-1, and a mixture at the respective rates, on a silt loam soil at 50, 75, and 100% of field capacity. For the flood timing experiment, tetflupyrolimet was applied to 2- to 3-leaf barnyardgrass at 134 g ai ha-1, and a flood was established at 4 hr after treatment (HAT) and 5 and 10 d after treatment (DAT). Barnyardgrass control with a tetflupyrolimet and clomazone mixture was comparable to clomazone plus quinclorac when averaged over all evaluations on silt loam and clay texture soils (≥91%). Soil moisture interacted with herbicide treatments for PRE and POST barnyardgrass efficacy when averaged over DAT, with tetflupyrolimet plus clomazone generally providing the greatest and most consistent control across regimes. Flooding barnyardgrass at 4 HAT provided superior control to later flood timings. Tetflupyrolimet is an effective residual barnyardgrass herbicide, and the addition of clomazone will aid in providing consistent control across varying soil moisture conditions.

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.

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.