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Crop losses from weed interference have a significant effect on net returns for producers. Herein, potential corn yield loss because of weed interference across the primary corn-producing regions of the United States and Canada are documented. Yield-loss estimates were determined from comparative, quantitative observations of corn yields between nontreated and treatments providing greater than 95% weed control in studies conducted from 2007 to 2013. Researchers from each state and province provided data from replicated, small-plot studies from at least 3 and up to 10 individual comparisons per year, which were then averaged within a year, and then averaged over the seven years. The resulting percent yield-loss values were used to determine potential total corn yield loss in t ha−1 and bu acre−1 based on average corn yield for each state or province, as well as corn commodity price for each year as summarized by USDA-NASS (2014) and Statistics Canada (2015). Averaged across the seven years, weed interference in corn in the United States and Canada caused an average of 50% yield loss, which equates to a loss of 148 million tonnes of corn valued at over U.S.$26.7 billion annually. Nomenclature: Corn, Zea mays L.

Weeds are one of the most significant, and controllable, threats to crop production in North America. Monetary losses because of reduced soybean yield and decreased quality because of weed interference, as well as costs of controlling weeds, have a significant economic impact on net returns to producers. Previous Weed Science Society of America (WSSA) Weed Loss Committee reports, as chaired by Chandler (1984) and Bridges (1992), provided snapshots of the comparative crop yield losses because of weeds across geographic regions and crops within these regions after the implementation of weed control tactics. This manuscript is a second report from the current WSSA Weed Loss Committee on crop yield losses because of weeds, specifically in soybean. Yield loss estimates were determined from comparative observations of soybean yields between the weedy control and plots with greater than 95% weed control in studies conducted from 2007 to 2013. Researchers from each US state and Canadian province provided at least three and up to ten individual comparisons for each year, which were then averaged within a year, and then averaged over the seven years. These percent yield loss values were used to determine total soybean yield loss in t ha−1 and bu acre−1 based on average soybean yields for each state or province as well as current commodity prices for a given year as summarized by USDA-NASS (2014) and Statistics Canada (2015). Averaged across 2007 to 2013, weed interference in soybean caused a 52.1% yield loss. Based on 2012 census data in the US and Canada soybean was grown on 30,798,512 and 1,679,203 hectares with production of 80 million and 5 million tonnes, respectively. Using an average soybean price across 2007 to 2013 of US $389.81 t−1 ($10.61 bu−1), farm gate value would be reduced by US $16.2 billion in the US and $1.0 billion in Canada annually if no weed management tactics were employed. Nomenclature: Soybean, Glycine max (L.) Merr Las malezas son una de las amenazas más significativas y controlables para la producción agrícola en Norteamérica. Las pérdidas monetarias producto de la reducción en el rendimiento de la soja y la disminución en la calidad debido a la interferencia de malezas y al costo de controlar a estas, tiene un impacto económico significativo en la rentabilidad de los productores. Reportes previos del comité de pérdidas por malezas de la Sociedad Americana de la Ciencia de Malezas (WSSA), bajo la dirección de Chandler (1984) y Bridges (1992) brindaron imágenes temporales de las pérdidas de rendimiento comparativas causadas por malezas en diferentes regiones geográficas y cultivos dentro de estas regiones después de la implementación de tácticas de control de malezas. Este manuscrito es un segundo reporte del comité actual de pérdidas por malezas de WSSA sobre pérdidas en rendimiento causadas por malezas, específicamente en soja. Los estimados de pérdida en rendimiento fueron determinados a partir de observaciones comparativas de rendimientos de soja entre testigos con malezas y parcelas con más de 95% de control en estudios realizados desde 2007 a 2013. Investigadores de cada estado de Estados Unidos y de cada provincia de Canada brindaron al menos tres y hasta 10 comparaciones individuales para cada año, las cuales fueron promediadas dentro de cada año, y luego promediadas para los siete años. Estos valores de porcentaje de rendimiento fueron usados para determinar la pérdida total en soja en t ha−1 y bu acre−1 con base en el promedio de rendimiento de soja para cada estado o provincia y el precio de grano para cada año como lo resumen USDA-NASS (2014) y Statistics Canada (2015). Promediando los años de 2007 a 2013, la interferencia de malezas en soja causó un 52,1% de pérdidas de rendimiento. Con base en los datos del censo de 2012 en Estados Unidos y Canada, se produjo soja en 30,798,512 y 1,679,203 hectáreas para una producción de 80 millones y 5 millones de toneladas, respectivamente. Usando una precio de la soja promedio para 2007 a 2013 de US $389.81 t−1 ($10,61 bu−1), el valor en puerta de finca se hubiera reducido en US $16.6 miles de millones en los Estados Unidos y $1.0 mil millones en Canada anualmente si no se hubieran empleado tácticas de manejo de malezas.

The history of weed science as a discipline has been a topic of interest for decades, but it is rare for researchers to consider publications prior to the 19th century or that were not focused on North America. In this article, the development of weed identification manuals in early modern England is documented out of two genres of premodern scientific writing: agricultural treatises and illustrated herbals. These two forms of writing intersected in the late 18th century with the publication of Thomas Martyn's four-volume Flora rustica, an illustrated guide to plants in British agricultural systems. We argue that the key characteristics of modern North American weed identification guides in English (the use of the term weed to categorize plants, descriptions of plant habitats, and the use of detailed descriptions and/or illustrations of plants for identification purposes) originated in these premodern texts.

In 2017, dicamba-resistant (DR) soybean was commercially available to farmers in the United States. In August and September of 2017, a survey of 312 farmers from 60 Nebraska soybeanproducing counties was conducted during extension field days or online. The objective of this survey was to understand farmers' adoption and perceptions regarding DR soybean technology in Nebraska. The survey contained 16 questions and was divided in three parts: (1) demographics, (2) dicamba application in DR soybean, and (3) dicamba off-target injury to sensitive soybean cultivars. According to the results, 20% of soybean hectares represented by the survey were planted to DR soybean in 2017, and this number would probably double in 2018. Sixty-five percent of survey respondents own a sprayer and apply their own herbicide programs. More than 90% of respondents who adopted DR soybean technology reported significant improvement in weed control. Nearly 60% of respondents used dicamba alone or glyphosate plus dicamba for POST weed control in DR soybean; the remaining 40% added an additional herbicide with an alternative site of action (SOA) to the POST application. All survey respondents used one of the approved dicamba formulations for application in DR soybean. Survey results indicated that late POST dicamba applications (after late June) were more likely to result in injury to non-DR soybean compared to early POST applications (e.g., May and early June) in 2017. According to respondents, off-target dicamba movement resulted both from applications in DR soybean and dicamba-based herbicides applied in corn. Although 51% of respondents noted dicamba injury on non-DR soybean, 7% of those who noted injury filed an official complaint with the Nebraska Department of Agriculture. Although DR soybean technology allowed farmers to achieve better weed control during 2017 than previous growing seasons, it is apparent that off-target movement and resistance management must be addressed to maintain the viability and effectiveness of the technology in the future. Nomenclature: dicamba; corn, Zea mays L.; soybean, Glycine max (L.) Merr.

Palmer amaranth–a fast-growing, challenging-to-control noxious weed that significantly reduces crop yields—was first found in Minnesota in September 2016 in conservation plantings sown with Palmer amaranth contaminated seed mixes. Minnesota Department of Agriculture (MDA) designated Palmer amaranth as a Prohibited Noxious Weed in 2015 and listed it as a Noxious Weed Seed in 2016 by emergency order. A genetic test to identify Palmer amaranth was simultaneously developed by multiple laboratories, providing a tool to limit its spread as a contaminant in seed. Seed companies adopted genetic testing methods for labeling seed for sale, thus reducing introductions via the seed pathway. Additionally, MDA determined that manure spread on crop fields from contaminated screenings fed to livestock resulted in new infestations. Limiting spread via these and other potential pathways was critical to successfully reducing the impact of Palmer amaranth. MDA, University of Minnesota (UMN) Extension, Conservation Corps Minnesota and Iowa (CCMI), farmers, and other partners are working to eradicate these infestations before they can spread. In 2016, 35 sites were sown with Palmer amaranth–contaminated seed mixes. Palmer amaranth was found at eight (23%) of these sites. Management with intensive scouting, torching, prescribed burning, and herbicide application was implemented in 2016 and 2017. By 2018, no Palmer amaranth was found at any of these sites. Similar success to newer infestations in 2018, 2019, and 2020 was achieved using the same methods. MDA recorded management activities and documented a comprehensive timeline of Palmer amaranth in Minnesota. This timeline provides a story of success and challenges in combating and eradicating Palmer amaranth. Nomenclature: Palmer amaranth; Amaranthus palmeri S. Watson

Potential yield losses in grain sorghum due to weed interference based on quantitative data from the major grain sorghum-growing areas of the United States are reported by the WSSA Weed Loss Committee. Weed scientists and extension specialists who researched weed control in grain sorghum provided data on grain sorghum yield loss due to weed interference in their region. Data were requested from up to 10 individual experiments per calendar year over 10 yr between 2007 and 2016. Based on the summarized information, farmers in Arkansas, Kansas, Missouri, Nebraska, South Dakota, and Texas would potentially lose an average of 37%, 38%, 30%, 56%, 61%, and 60% of their grain sorghum yield with no weed control, and have a corresponding annual monetary loss of US $19 million, 302 million, 7 million, 32 million, 25 million, and 314 million, respectively. The overall average yield loss due to weed interference was estimated to be 47% for this grain sorghum-growing region. Thus, US farmers would lose approximately 5,700 million kg of grain sorghum valued at approximately US $953 million annually if weeds are not controlled. With each dollar invested in weed management (based on estimated weed control cost of US $100 ha-1), there would be a return of US $3.80, highlighting the return on investment in weed management and the importance of continued weed science research for sustaining high grain sorghum yield and profitability in the United States. Nomenclature: Grain sorghum, Sorghum bicolor (L.) Moench

This report updates the incidence of herbicide-resistant (HR) weeds across western Canada from the last report covering 2007 to 2011. This third round of preharvest surveys was conducted in Saskatchewan in 2014 and 2015, Manitoba in 2016, and Alberta in 2017, totaling 798 randomly selected cropped fields across 28 million ha. In addition, we screened 1,108 weed seed samples submitted by prairie growers or industry between 2012 and 2016. Of 578 fields where wild oat seed was collected, 398 (69%) had an HR biotype: 62% acetyl-CoA carboxylase inhibitor (WSSA Group 1) resistant, 34% acetolactate synthase inhibitor (Group 2) resistant, and 27% Group 1+2 resistant (vs. 41%, 12%, and 8%, respectively, in the previous second-round surveys from 2007 to 2009). The sharp increase in Group 2 resistance is the result of reliance on this site of action to manage Group 1 resistance and the resultant increased selection pressure. There are no POST options to control Group 1+2–HR wild oat in wheat or barley. The rise of Group 2 resistance in green foxtail (11% of sampled fields) and yellow foxtail (17% of Manitoba fields), which was not detected in the previous survey round, parallels the results for wild oat resistance. Various Group 2–HR populations of broadleaf weeds were confirmed, with cleavers and field pennycress being most abundant. Results of submission-sample testing reflected survey results. Although not included in this study, a postharvest survey in Alberta in 2017 indicated widespread Groups 2, 4 (dicamba), and 9 (glyphosate) resistance in kochia and Group 2 resistance in Russian thistle. These surveys bring greater awareness of HR weeds to growers and land managers at local and regional levels, and highlight the urgency to preserve herbicide susceptibility in our key economic weed species. Nomenclature: Acetolactate synthase inhibitor; acetyl-CoA carboxylase inhibitor; dicamba; glyphosate; Cleavers, Galium spp.; field pennycress, Thlaspi arvense L.; green foxtail, Setaria viridis (L.) P. Beauv.; kochia, Bassia scoparia (L.) A. J. Scott; Russian thistle, Salsola tragus L.; wild oat, Avena fatua L.; yellow foxtail, Setaria pumila (Poir.) Roem. & Schult

Weeds represent one of the most important biotic threats to agricultural plant health, and the potential global impact of weeds on crop yields is similar to that of all other pests (animal pests and pathogens) combined. Canola is the most-grown crop in Canada based on seeded area and generates on average Can$29.9 billion in economic activity each year. The objective of this report, sponsored by the Weed Science Society of America Weed Loss Committee, was to provide an updated estimate of potential yield and monetary losses due to weed interference in spring canola grown in Canada and the United States. Quantitative yield data from field experiments were provided by researchers and weed science professionals in the northern Great Plains region; the major canola-producing area of North America. Overall, 89 yield loss estimates were compiled, covering the 18-yr period from 2003 to 2020. Average canola yield losses due to weed interference in Alberta, Saskatchewan, Manitoba, and North Dakota were 35%, 30%, 18%, and 28%, respectively. Potential yield losses weighted by canola harvested area averaged 30%, 28%, and 30% for Canada, the United States, and both countries combined, respectively. Therefore, unfettered weed interference in spring canola represents a potential monetary loss of Can$2.21 billion, $0.16 billion, and $2.37 billion for farmers in Canada, the United States, and both countries combined. The realization of such losses could manifest through continued selection for herbicide-resistant weeds, indicating the critical need for canola farmers to diversify resistance selection pressures by implementing proactive integrated weed management programs. Nomenclature: Canola; Brassica napus L.

Earlier reports have summarized crop yield losses throughout various North American regions if weeds were left uncontrolled. Offered here is a report from the current WSSA Weed Loss Committee on potential yield losses due to weeds based on data collected from various regions of the United States and Canada. Dry bean yield loss estimates were made by comparing dry bean yield in the weedy control with plots that had >95% weed control from research studies conducted in dry bean growing regions of the United States and Canada over a 10-year period (2007 to 2016). Results from these field studies showed that dry bean growers in Idaho, Michigan, Montana, Nebraska, North Dakota, South Dakota, Wyoming, Ontario, and Manitoba would potentially lose an average of 50%, 31%, 36%, 59%, 94%, 31%, 71%, 56%, and 71% of their dry bean yield, respectively. This equates to a monetary loss of US $36, 40, 6, 56, 421, 2, 18, 44, and 44 million, respectively, if the best agronomic practices are used without any weed management tactics. Based on 2016 census data, at an average yield loss of 71.4% for North America due to uncontrolled weeds, dry bean production in the United States and Canada would be reduced by 941,000,000 and 184,000,000 kg, valued at approximately US $622 and US $100 million, respectively. This study documents the dramatic yield and monetary losses in dry beans due to weed interference and the importance of continued funding for weed management research to minimize dry bean yield losses. Nomenclature: dry bean, Phaseolus vulgaris L.

Weeds pose a significant threat to Oregon field crops by reducing yields and compromising the quality of the harvested products. In fall 2024, Oregon stakeholders were surveyed to identify the key challenges and needs related to weed management in field crops. The survey consisted of eight questions, developed based on expert input and review of relevant literature, divided into three sections: respondent demographics, resource and support needs, and current weed management challenges and economic impacts. A total of 184 responses were collected statewide, with growers and crop consultants as the primary participants. Most respondents were from western Oregon, which may introduce a geographic bias to the findings. Respondents expressed particular interest in new herbicide technologies and herbicide resistance. Field days were the most preferred method for receiving weed management information. Annual bluegrass, Italian ryegrass, and roughstalk bluegrass were reported as the most problematic grass weeds, while wild carrot was the most problematic broadleaf weed. Most respondents reported an average weed control cost of US$125 to US$250 per hectare, and the majority indicated they were very concerned about herbicide resistance in their fields. The results from this survey will help guide future research and outreach efforts to improve weed management strategies in Oregon's field crops. Nomenclature: Annual bluegrass; Poa annua L.; Italian ryegrass; Lolium multiflorum Lam.; roughstalk bluegrass; Poa trivialis L.; wild carrot; Daucus carota L.