Integrated Management Techniques to Combat Potential Shifts in Horseweed Emergence

This is an ARDP Applied Research (single-function) project. We seek to develop integrated pest management strategies for horseweed (Conyza canadensis), also known as marestail. Over the last two decades, this weed has progressed from a nuisance species characterized as a winter annual to one of the most troublesome weeds within soybean production. Selection for resistance to widely used herbicides, creation of optimum emergence and growth conditions by shifting to no-till production systems, and increasing evidence that seedlings emerge in the fall through the following summer contribute to the severity of horseweed occurrence, abundance, and impact. Our first objective is to investigate key aspects of horseweed biology across several soybean production areas, including emergence timing and over-wintering success. Findings will inform our second objective, which is to combine the use of cover crops and selective herbicides to limit establishment of horseweed, a vulnerable point in the plant's life cycle. These objectives will be accomplished through a common garden experiment and field trials in four states. Our project examines "innovative, ecologically- based, sustainable IPM strategies and systems that address regional and/or national IPM priorities"-the major focus for applied research projects within the ARDP program area with the CPPM program. This project addresses national IPM roadmap goals, including adoption of cost-effective IPM tactics for horseweed management while reducing dependency on herbicides. Ultimately, improvements in soybean production efficiency can be made while reducing potential human health and environmental risks.