Increasing the resilience of organic vegetable systems through agroecological weed management

Abstract

Despite many efforts, weeds remain a major limitation to crop production, causing substantial yield losses and increasing management costs. Conventional management has focused on eliminating weeds through strong selection pressures, like herbicides and tillage. However, overreliance on these approaches led to herbicide resistance, soil erosion, and environmental concerns; highlighting the need for sustainable strategies. Ecological weed management (EWM) offers an alternative approach by shifting the focus from weed eradication to managing populations through ecological processes. However, key knowledge gaps remain for the application of EWM, including limited understanding of weed communities in organic vegetable systems, insufficient consideration of the impact of management decisions on crop yield and quality, uncertainty in how climate change may alter weed management strategies, and a lack of educational approaches that effectively teach EWM. To address these gaps, this dissertation integrates field experiments, controlled-environment studies, on-farm surveys, and educational research. Field experiments quantified the critical period of weed control (CPWC) in organically grown carrots, incorporating both yield and quality, and evaluating opportunities for value-added use of imperfect produce. Growth chamber experiments assessed how elevated carbon dioxide (CO 2) influenced crop and weed growth, altering the length of the CPWC. On-farm surveys characterized weed community composition and functional traits across farms, crops, and years. Finally, an experiential learning exercise was developed to improve student understanding of EWM concepts and scientific writing. Four main results emerged from this dissertation. First, the CPWC differed depending on whether yield or quality was prioritized, indicating that weed management based solely on yield may result in unexpected negative results. Second, elevated CO 2 altered plant growth and shifted CPWC timing, suggesting that climate change may modify management recommendations. Third, farm identity and year were the dominant factors determining functional diversity, indicating that farm-level management acts as a dominant filter shaping weed communities. Finally, the teaching exercise improved students' understanding of ecological underpinning of weed management and their scientific writing skills. Overall, this research demonstrates how integrating ecological principles into weed management can improve decision-making, enhance resilience in organic vegetable systems, and better prepare future scientists and land managers to address emerging agricultural challenges.