Location: Global Change and Photosynthesis Research
2025 Annual Report
Objectives
Objective 1: Develop control measures for weeds in vegetables, fruits, and specialty crops. [NP304, C2, PS 2A]
Objective 2: Determine herbicide residues in harvested product. [NP 304, C2, PS 2A]
Approach
Candidate herbicides for use in minor crops will be identified. Herbicides alone or in combination with other tactics will be evaluated under field conditions and crop and/or weed responses will be determined.
Progress Report
This report summarizes progress for this project, which began on October 1, 2024 and terminated on September 30,2025. ARS researchers supported a comprehensive field survey spanning over 400 processing snap bean and lima bean fields across major U.S. production regions (Midwest, Northeast, Northwest) from 2019 to 2023. Although not among the major crops, snap bean and lima bean are two crops with substantial production in the US. As with all crops, weed growth can reduce yield by competing with the crop. Some weeds can also complicate harvesting by interfering with machinery and workers, increasing costs. A first step toward effective nationwide management of weeds in these systems is to survey the species of weeds occurring in production fields and practices used to control them. This work represents the first nationwide characterization of weed communities and management practices in these two crops. This work provides foundational knowledge to guide future integrated weed management strategies in U.S. snap bean and lima bean production systems, by providing agriculture technology companies and farmers information about species, and thus which products, can effectively manage weeds in these fields. This information has been conveed to the public via three published manuscripts and one in progress as well as via direct communication during outreach events.
Sub-objective 1.2: ARS researchers in Urbana, Illinois, are explored solutions to manage weeds that currently escape control. Several preemergence herbicides suppress weed species; however, snap bean tolerance to such herbicides is poorly documented. This research identified two herbicides, dimethenamid-P and lactofen, that appear safe for use in snap bean production. The impact of this research supports an effort to develop a federal label for use of dimethenamid-P and lactofen on snap bean. Such an outcome would be a welcome addition to the weed management arsenal in the crop. This research is published in Weed Technology. As follow up to these findings, , in 2024 we conducted a trial to find safe and effective application methods for lactofen in large yield trials utilizing two commercial snap bean cultivars treated with varying rates of lactofen. Preliminary results indicate lactofen is an effective short term PRE herbicide if it is followed with a POST herbicide.
Sub-objective 1.3: Snap bean varieties differ in their tolerance to herbicides, and identifying naturally tolerate varieties can be used to identify the genes responsible for tolerance. Once the gene is identified, conventional breeding can bring the gene into commercial line, giving growers more management options. ARS researchers in Urbana, Illinois, continue to use natural variation in snap bean varieties to investigate tolerance to various herbicides including flumioxazin. They found that snap bean's ability to survive an application of the herbicide flumioxazin is due to multiple physiological pathways that are controlled by a master element . The existence of a single element able to regulate the expression of a large number of genes involved in stress tolerance is of high interest for basic science, because such genetic regulation provides information about fundamental aspects of how plants responds to their environment, and applied crop breeding, because it provides a clear target for breeding this trait into commercial lines. Conceivably, excessive reliance on flumioxazin or related herbicides for weed control could lead to weed species that are enriched in tolerance mechanisms identified in this research. This work is published in Frontiers in Plant Science.
Sub-objective 1.4: ARS researchers in Urbana, Illinois, have also done research that helps the popcorn industry. The United States grows and consumes more popcorn than any other nation, with a market value of approximately USD 6 billion in 2024. Herbicides registered on popcorn often are available for use on yellow kernel hybrids but not white kernel hybrids. Nicosulfuron is one such herbicide because of concerns about crop damage. Assessing the feasibility of its use in popcorn requires a survey of resistance in popcorn lines. An evaluation of nicosulfuron resistance in 362 popcorn varieties identified two groups of popcorn. The first group, dominated by yellow kernel accessions, had limited genetic diversity and tolerance to nicosulfuron herbicide compared to the second group, dominated by white kernel accessions and sensitivity to nicosulfuron. Candidate genes conditioning response to nicosulfuron appear to differ from previous research findings in field corn and sweet corn. The research showed that popcorn population, not kernel color, accounts for differential response to nicosulfuron. This work is published in Crop Science. In 2024, a new maize herbicide (tolpyralate) was applied to this popcorn germplasm collection and it was found that a small number of popcorn inbred lines unexpectedly displayed severe tolpyralate injury. This led to the discovery that tolpyralate resistance is due to a different gene than related herbicides and underscores the need to test these herbicides on diverse panels to avoid unintended negative impacts on the crop.
Accomplishments
1. First nationwide characterization of weed communities and management practices in these two crops. Weed management can effectively improve profits by increasing crop yield and reduce costs, but lowering effort in maintaining and harvesting crops, but in snap bean, there is no understanding of nationwide prevalence of the species of weeds that grown in snap bean fields or the practices use to manage them. Without this knowledge, farmers and ag tech companies cannot develop strategies or products to target the problems. We identified the most common weeds and management practices in snap bean by surveying more than 400 fields. This work provides foundational knowledge to guide future integrated weed management strategies in U.S. snap bean and lima bean production systems. Companies and farmers can use this information to develop and select appropriate herbicides. This information has been shared with farmers and other stakeholder by three manuscripts in publication and a fourth in progress as well as at outreach events.
2. Identified two new herbicides for use with snap bean. Farmers benefit from a variety of available herbicides in their cropping systems since multifaceted approaches to weed management are more effective at control and reduce the development of tolerance. Many herbicides have never been tested in snap bean, and thus they are not approved for use in that crop. A straightforward approach to expanding farmer choices is to test existing herbicides. Two herbicides (dimethenamid-P and lactofen) appear safe for use in snap bean production. Published manuscript in Weed Technology. Lactofen treated snap bean yield trials in 2024. Preliminary results indicate lactofen is an effective short term PRE herbicide if it is followed with a POST herbicide. This information can be used to approve use of these herbicides leading to greater choice and more effective control of weeds for farmers.
3. Identified genetic elements related to herbicide tolerance in popcorn. Many herbicide are approved for use in field corn, but several of those are not approved for use with popcorn because of concerns of crop damage. The mechanisms responsible for tolerate in popcorn are not known, but given the close relationship with field corn, it is likely that tolerance exists in popcorn populations and the mechanisms could be identified. We identified the existence of a single element able to regulate the expression of a large number of genes involved in stress tolerance is of high interest for basic science and applied crop breeding. With knowledge of the genetic location, breed programs can incorporate this trait into commercial lines, providing farmers with an new tool to manage weeds in popcorn. Results have been shared with the public by a published manuscript.
4. Popcorn population, not kernel color, accounts for differential response to nicosulfuron. An understanding of the traits responsible for tolerance guides herbicide selection. Currently, nicosulfuron is approved for use in corn based on kernel color, but if this approach is incorrect, it can lead to inappropriate use of herbicide, potentially applying it in situations where it damages the crop. We examined whether kernel color itself was related to tolerance and found that it was not. The underlying mechanism for tolerance is more complicated and is not related to kernel color. In 2024, a small number of popcorn inbred lines was identified as tolpyralate sensitive. This understanding can lead to better labeling for this herbicide, protecting farmers from potential crop damage, and can guide breeding programs to develop tolerant popcorn lines. This work was shared with the public by a published manuscript in Crop Science.
Review Publications
Pavlovic, P., Colquhoun, J., Korres, N., Liu, R., Lowry, C., Peachey, E., Scott, B., Sosnoskie, L., Vangessel, M., Williams, M. 2024. Weed communities of snap bean fields in the United States. Weed Science. https://doi.org/10.1017/wsc.2024.76.
Pavlovic, P., Colquhoun, J., Korres, N., Liu, R., Lowry, C., Peachey, E., Scott, B., Sosnoski, L., Vangessel, M., Williams, M. 2025. Crop and weed management practices of snap bean (Phaseolus vulgaris) production fields in the United States. HortScience. https://doi.org/10.21273/HORTSCI18254-24.
Takenaka, Y., Pavlovic, P., Vangessel, M., Scott, B., Colquhoun, J., Williams, M. 2025. Field surveys of bush lima bean reveal shortcomings in weed management. HortScience. https://doi.org/10.21273/HORTSCI18583-25.
Khan, J., Hausman, N.E., Saballos, A., Landau, C.A., Williams, M. 2024. Snap bean tolerance to preemergence applications of dimethenamid-P, flumioxazin, lactofen, metribuzin, saflufenacil, and sulfentrazone. Weed Technology. https://doi.org/10.1017/wet.2024.39.
Williams II, M.M., Hausman, N.E., Saballos, A., Landau, C.A., Brooks, M.D., Flannery, P., Tracy, W., Thompson, C. 2024. First report of severe tolpyralate sensitivity in corn (Zea mays) discovers a novel genetic factor conferring crop response to a herbicide. Pest Management Science. 80(3):1645-1653. https://doi.org/10.1002/ps.7896.
Sullivan, M., Williams II, M.M., Studer, A. 2023. Genetic diversity of North American popcorn germplasm and the effect of population structure on nicosulfuron response. Crop Science. 63(5):2894-2912. https://doi.org/10.1002/csc2.21039.
Saballos, A.I., Brooks, M.D., Tranel, P.J., Williams II, M.M. 2024. Mapping of flumioxazin tolerance in a snap bean diversity panel leads to the discovery of a master genomic region controlling multiple stress resistance genes. Frontiers in Plant Science. https://doi.org/10.3389/fpls.2024.1404889.