Influence of Integrated Weed Management Practices on Glyphosate Resistant Horseweed Population Dynamics.
Vince M. Davis, Greg R. Kruger, Andrew M. Westhoven, and William G. Johnson. Purdue University, Lilly Hall of Life Sciences, 915 West State St., West Lafayette, IN 47907
Horseweed, Conyza canadensis, is an increasingly common and problematic weed in no-till soybean production due to the frequent occurrence of biotypes resistant to glyphosate in the eastern cornbelt. The objective of this study was to determine the influence of crop rotation, cover crops, residual non-glyphosate herbicides, and burndown application timing on the population dynamics of glyphosate resistant (GR) horseweed. A long-term field study was established in a no-tillage field at a site that contained a moderate infestation of GR horseweed (approximately 1 plant m-2). The experiment was a split-plot design with crop rotation (soybean-corn or soybean-soybean) as main plots and management systems as sub plots. Management systems were evaluated by monitoring seed producing adult horseweed plant density, viable horseweed seedbank density, and crop yields. Crop rotation did not influence plant or seedbank density. Spring applied burndown applications were more effective at reducing plant and seedbank densities than fall burndown applications. Spring-applied non-glyphosate residual herbicides and winter wheat cover crops were the most effective at reducing adult horseweed and seedbank densities, and protecting crop yields.