Weeds incur up to A$4 billion in economic loss annually to Australian agriculture. Despite this knowledge, few quantitative data exist on yield loss and control costs caused by weeds. This article discusses the economic cost of managing the invasive Navua sedge weed to the grazing and cropping (sugarcane) industries of northern Queensland, Australia, following its introduction into the region in the 1970s. Between 2020 and 2022, through a survey questionnaire distributed to affected farmers, information on control cost, yield loss, and infestation history were documented. Collated data were analyzed using primarily nonparametric statistics due to the skewed or qualitative nature of many of the responses. The weed has invaded farming properties over the past 10 to 20 yr, the infestation level is considered to be low to moderate (median, 22.5%), and it varies appreciably among properties. The median cost of managing Navua sedge was A$72.91/ha when the study was conducted (the current value is now A$82.06). Neither this cost nor the type of management tactics (chemical vs. integrated weed management [IWM]) did not vary between land use types; however, labor, relative to chemical and machinery costs, was the greatest expense. The currently approved herbicide, halosulfuron-methyl (Sempra), is largely ineffective in controlling the weed due to its inability to deplete the weed’s belowground tubers. Correlation analyses suggest that control costs will continue to increase with increasing Navua sedge infestation over time, especially in grazing lands. Farmers are highly aware of the challenge of managing this new weed. Farmers are using a myriad of strategies, including being willing 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.

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 to turf using an RPAAS, focusing on large crabgrass control with quinclorac. The research was conducted in 2022 at two sites in College Station, TX. 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 four-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 to turf. This study also suggests that large crabgrass can be controlled using RPAAS with a range of spray nozzle types at low application volumes to turfgrass. Further research is needed to assess the efficacy of RPAAS-based herbicide applications across a range of herbicides, weed species, and environmental conditions.

Fall-planted cover crops are becoming popular among growers in the Midwest for various reasons, including their ability to suppress weeds. Cereal rye is the cover crop most often planted 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 glyphosate alternative acetyl-CoA carboxylase (ACCase)-inhibiting herbicides for terminating cereal rye 15 d before soybean planting (DBSP), at soybean planting day (SPD), and 15 d after soybean planting (DASP) and their effect on weed control, density, biomass, soybean plant stand, and soybean grain yield. Field experiments were conducted from 2018 to 2020 at South Central Ag Lab near Clay Center, Nebraska. Cereal rye biomass collected 15 d 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, at the 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 applications of fluazifop-P-butyl, fluazifop-P-butyl/fenoxaprop-P-ethyl, quizalofop-P-ethyl, and glyphosate. Similarly, at the SPD and 15 DASP termination timings, 66% and 31% control of cereal rye, respectively, were recorded after clethodim was used compared with greater than 92% control after other ACCase-inhibitors and glyphosate were used. Palmer amaranth control at the R5 soybean growth stage was 70%, 88%, and 96%, respectively, at 15 DBSP, SPD, and 15 DASP. Soybean yield was reduced to 2,184 kg ha−1 when cereal rye was terminated at 15 DASP compared with 4,566 kg ha−1 when it was terminated at SPD, and 4,460 kg ha−1 at 15 DBSP.

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 4 site-years with a split-split-plot treatment arrangement where the whole plot was soybean trait (LibertyLink® GT27 or Enlist® E3), 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 (ANOVA) 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 wk 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 with Enlist® E3 soybean planted in 76-cm rows with PRE herbicide treatment. The greatest income in the irrigated site-year was with Enlist® E3 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.

A limited number of herbicides and sites of action are registered for use on sugarcane in Louisiana. Repeated use of the same sites of action can lead to the evolution of herbicide resistance by weeds. Therefore, it is critically necessary 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 that includes mesotrione, bicyclopyrone, atrazine, and S-metolachlor, along with more common herbicides (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 nontreated 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% 2 wk after treatment. Indaziflam and combined application of mesotrione, bicyclopyrone, atrazine, and S-metolachlor injury was at or under 10% 2 wk after treatment. The tolerance of sugarcane for these herbicides suggests that they can be incorporated into weed management strategies in sugarcane production. These herbicides would increase the sites of action available to be applied to sugarcane and help mitigate the risk of herbicide-resistant weeds.

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 to 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 wk) after crop emergence. The results show 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 to 994 growing degree days (GDD), corresponding to 14 to 85 d after emergence (DAE). These findings emphasize the importance of implementing effective weed control measures from 14 to 85 DAE in the Lower Yangtze Valley to prevent crop losses exceeding a 5% yield loss threshold.

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 (1) to 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) to 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-fold and 3.2- to 12.2-fold reduced sensitivity to imazamox compared to ARCH21B and SOR, respectively. Similarly, ARCH45R and 49R had 2.5- to 6.0-fold 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.

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 surveys of corn production costs in 2021 and soybean production costs in 2023, carried out by the U.S. Department of Agriculture–National Agricultural Statistics Service (USDA-NASS) through the 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 used 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, applied to 79%, 65%, and 47% of corn production areas, respectively, planted in 2021. Similarly, glyphosate (in various salt forms) was the most widely applied herbicide in soybean production, 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 hectarage, respectively, planted in 2023. 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 US$3.2 and US$4.1 billion in corn and soybean production in 2021 and 2023, respectively.

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 Corp. 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 three-leaf cotton (early-postemergence or EPOST) or to seven-leaf cotton (mid-postemergence or MPOST). No difference in cotton stand was observed between isoxaflutole or prometryn preemergence 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 seven-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.

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, and 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 mid-season. The 2024 experiment included a combination treatment of PPI sulfosulfuron, chemigated rimsulfuron, and foliar maleic hydrazide, which resulted in <4 broomrape clusters plot−1. 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.

Purple witchweed is a hemiparasitic plant that significantly affects sorghum yields in semiarid regions. It also affects crops such as corn, millets, and rice. Developing purple witchweed-resistant sorghum varieties is an essential element in integrated purple witchweed management. This study evaluated the response of 48 sorghum genotypes to purple witchweed grown both in pots and in field conditions. Resistant varieties (Berhan and Framida) and susceptible varieties (Assosa-1, Adukara, and ETSL102967) were used as controls. The findings revealed substantial variability among the sorghum landraces in their response to purple witchweed. Purple witchweed density was less when seeds were grown with early maturing sorghum genotypes, while late-maturing genotypes were more susceptible to the weed. Notably, the ETSL102969 landrace showed strong resistance, comparable to that of Berhan. Additionally, the ETSL102970 landrace demonstrated superior resistance to purple witchweed compared to Framida. Based on these results, ETSL102969 and ETSL102970 are recommended as valuable sources of resistance for breeding programs aiming to improve sorghum resistance against purple witchweed in Ethiopia.

Wild oat is a significant weed of cropping systems in the Canadian Prairies. Wild oat resistance to herbicides has increased interest in the use of nonchemical 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 the effects of crop rotation maturity, harvest management, and harvest weed seed control on wild oat, a study was conducted from 2016 to 2018 at four locations in the Canadian Prairies. Two-year crop rotations with either early, normal, or late-maturing 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 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 exhibited lower biomass in swathed crops than straight-cut crops. Wild oat seedbank levels reflected a similar trend with the lowest densities occurring in early maturing rotation, then the normal maturity rotation, and the late maturing rotation, which 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 management effects from earlier maturing crops.

Cleavers, an annual or winter annual broadleaf weed in the Rubiaceae family, has become troublesome in the wheat fields of the Huang-Huai-Hai region in China due to its herbicide resistance. In North America the common name of the plant is stickwilly; in China it known as cleavers. Four populations of cleavers (JS-15, SD-10, JS-22, and AH-20) were collected from wheat fields in Jiangsu, Shandong, and Anhui provinces, where the plant was not being controlled with applications of florasulam. The aims of this study were to identify the herbicide resistance patterns and investigate the mechanism underlying florasulam resistance. Whole-plant dose-response experiments revealed a notable variation in the degree of resistance exhibited by three specific populations toward florasulam, in comparison to the most sensitive population (S and AH-9), with the highest resistance index reaching 841.4. A gene-sequencing assay for acetolactate synthase (ALS) found that plants that were resistant to ALS from the JS-15, JS-22, and AH-20 populations 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 JS-15, JS-22, and AH-20 plants was greatly resistant to florasulam relative to plants that are susceptible. Additionally, according to the resistance rating system, all resistant populations were susceptible to carfentrazone-ethyl + MCPA-sodium and bipyrazone + fluroxypyr-methyl. AH-20, JS-15, and JS-22 exhibited resistance to selected ALS, 4-hydroxyphenylpyruvate dioxygenase (HPPD), and photosystem II (PS II) complex inhibitors, demonstrating RR and RRR resistance profiles, whereas AH-9 displayed sensitivity to virtually all tested agents. The SD-10 population, on the other hand, exhibited RR and RRR resistance to HPPD and PS II inhibitors, and sensitivity to tribenuron-methyl. These findings indicate that a target site–based mechanism drives resistance to the ALS inhibitor florasulam in populations of cleavers, but nontarget site resistance may also have contributed to resistance, but this was not investigated. Other herbicides with different sites of action were tested and were active against cleavers.