Ecological, physiological, and theoretical foundations for integrated weed management in herbicide-resistant agroecosystems

Abstract

The widespread adoption of transgenic herbicide-resistant cultivars has led to an overreliance on herbicides, resulting in a reduction in the diversity of weed management practices. This oversimplified approach has decreased selective heterogeneity, leading to repeated evolution of herbicide resistance that threatens conventional agroecosystems. To ensure the long-term sustainability of agriculture, this challenge must be addressed using ecologically grounded, integrated weed management strategies. I first address a broader question: Is herbicide resistance gene-stacking a sustainable approach for weed management? We aim to investigate the eco-evolutionary and management implications of adopting forthcoming glyphosate-, dicamba-, and glufosinate-resistant sugarbeet cultivars in Montana cropping systems through surveys and greenhouse studies. Two evolutionary adaptations, herbicide resistance and delayed or extended emergence, were evident and could aid weed populations in evading early-season tillage and herbicide applications. Our results validate growers' concerns about multiple herbicide resistance in weed populations in Montana sugarbeet cropping systems, suggesting the need for an integrated weed management approach to mitigate the problem. Subsequently, I discuss the humidity-dependent response and application complexity associated with glufosinate, an additional trait of the forthcoming transgenic sugarbeet cultivar. In greenhouse and laboratory experiments, I addressed how long kochia [Bassia scoparia (L.) A. J. Scott] and common lambsquarters (Chenopodium album L.) require higher relative humidity (RH) after glufosinate applications. Species-specific glufosinate efficacy was observed in B. scoparia and C. album as a function of RH. This study provides fundamental information needed to schedule glufosinate applications to optimize its efficacy. Finally, I apply ecological principles to assess crop-weed competitive interactions. Specifically, I evaluate the integration of limiting similarity theory and a trait-based approach to assess weed biomass and seed production in different crops. This study demonstrates a positive correlation between crop-weed functional similarity and the intensity of competition. The findings of this study provide a foundational framework for designing integrated weed management programs across diverse agroecosystems. Overall, my research (1) emphasizes that relying solely on a single management practice diminishes the stewardship of forthcoming herbicide-resistant crop cultivars with stacked characteristics and (2) highlights the importance of integrating basic ecological principles into applied weed management to diversify selection pressure.