Weed management is one of, if not the, greatest challenge for organic crop production

The Pennsylvania State University received a $935,000 Project Grant from the U.S. Department of Agriculture's National Institute of Food and Agriculture (NIFA) under the Integrated Programs (CFDA 10.303) on September 15, 2025. The four-year project, extending through September 14, 2029, addresses weed management challenges in organic crop production by investigating how soil microbes can naturally reduce weed seed populations. Penn State will conduct complementary field experiments examining organic soil amendments and perennial forage crop rotations to identify microbial taxa that increase weed seed mortality and determine which management practices promote beneficial microbial populations.

The project deliverables include: (1) two field experiments—one in field crops and one in vegetables—comparing organic soil fertility amendments to evaluate their effects on weed seed mortality and soil microbiomes; (2) evaluation of a long-term Penn State organic experiment to assess how perennial forage crops influence weed seed mortality relative to standard annual crop rotations; (3) driver analysis using on-farm and on-station trials to identify soil factors and microbial communities affecting weed seed mortality; and (4) farmer advisory panel engagement and on-farm trials to transfer research findings to organic producers. The research will employ amplicon sequencing to characterize bacterial and fungal communities and tetrazolium testing to assess seed viability, ultimately providing organic farmers with practical crop management strategies to improve weed control without conventional herbicides.

Organic farmers rely on tillage for weed control; however, tillage is often less effective than conventional forms of weed management (e.g. herbicides) and therefore weeds can reduce yields in organic systems. Additionally, interest in ecologically produced food is increasing among the public. Soil microbes can infect and kill weed seeds, thereby reducing populations of problematic weed species. Determining what crop management approaches can increase microbially-mediated mortality of weed seeds in the soil could greatly improve the ability or organic farmers to control weeds. However, research has been limited on which microbial taxa can increase weed seed mortality, and what management factors promote those microbial populations.to address this knowledge GAP, we will conduct complementary field experiments. First (OBJ. 1), we will conduct two complementary experiments (one in field crops and one in vegetables) examining how organic soil amendments influence both weed seed mortality and microbiome, as well as the soil microbiome. To do this, we will compare organic soil fertility amendments that vary in chemical and nutrient quantities. Second (OBJ. 2), we will leverage a long-term organic experiment at PSU to evaluate how distinct perennial forage crops (compared to a standard organic annual crop rotation) influence weed seed mortality and microbiomes, as well as the soil microbiome. For both experiments, we will use amplicon sequencing to characterize the bacterial and funal communities within weed seeds, and tetrazolium tests to assess seed viability. Additionally (ONJ. 3), using a series of on-farm trials as well as our on-station trials, we will determine the drivers (e.g. soil abiotic factors and soil microbiome) of weed seed mortality and microbiomes. Finally in collaboration with organic farmers, (OBJ. 4) we will use our farmer advisory panel, on-farm trials, and other extension events to develop a mutual understanding of how soil fertility and crop rotations can be leveraged within organic systems to enhance weed seed mortality in the soil seedbank. We expect the proposed research to identify specific microbial taxa that are associated with greater mortality of weed seeds. The integrated research and extension publications and events (such as field days at on-farm sites, study circles, and presentations at grower meetings) will provide valuable information to organic farmers in how to manage the soil in ways that promote microbially mediated weed seed mortality. Ultimately, our proposed research will result in a greater understanding of how to use ecological approaches to manage weeds in organic systems. This proposed project aligns with the priorities in the organic transitions program by focusing on understanding the effects of organic management on populations of problematic weeds.