Abstract for: Despite modern advancements in cropping systems, why does herbicide resistance continue to outpace human innovation?
Herbicide weed resistance (HRW) remains a major concern in modern agriculture and has rapidly increased from the first case in 1957 to over 500 today. Despite this trend, herbicide treatments continue to be farmers’ preferred control method due to their low cost and efficiency relative to other methods (e.g., mechanical removal). Herbicide resistance weed development is recognized as the result of adaptive evolution by weed populations to selection pressure excreted by herbicides, causing the few HRW individuals surviving chemical treatment to pass down resistant traits to their offspring that upon emergence become a larger fraction of the total population. Our objective was to develop a simulation model of the links between weed population dynamics, agricultural crop management, and farmer decision-making processes that interact in unique ways to reinforce HRW. Results indicated that switching chemicals to alter weed selection pressure and reduce HRW accumulation did not always result in improved productivity and profit. Only under low commodity prices did switching treatments improve long-term profit per area, but also led to the greatest chemical accumulation and HRW seedbank levels in soil, which reinforced weed biomass and reduced crop yields in subsequent growing seasons (>2-3 years; an example “fixes that backfire”).