Integrating cover crops and herbicides for marestail management prior to soybean--Renewal

Marestail has become a major weed for soybean producers in Kentucky and throughout a broader geographic range. Its small seed size make this weed particularly troublesome for no-till soybean growers; its prolific, wind-blown seed can disperse far between fields and adjacent natural areas. Its extended emergence period also complicates management efforts. In addition to all of these traits, glyphosate resistant biotypes are now widespread throughout the western and central parts of the state. Thus, management tactics that integrate chemical options with cultural practices like the use of cover crops are desirable for this species. This project examines the integration of fall- and springapplied herbicides with fall-planted cover crops to improve management of marestail prior to soybeans. We are utilizing a site with a heavy infestation of fall-emerged marestail that has historically had spring emergence as well. Results from the first year showed that all herbicides were effective in reducing marestail density. However, an additional flush of marestail emergence following herbicide applications resulted in higher marestail density by soybean planting time. The cover crop residue was able to suppress emergence of this additional flush. Results from a second year of this project will allow us to make recommendations about best management practices for this species, help determine whether cover crops can substitute for an herbicide application, and develop cost comparisons for control options.