Conservation tillage systems, which cotton producers on the Texas Southern High Plains have used successfully for several years, have created new weed problems including horseweed and Russian thistle. The objectives of this study were: to evaluate preplant weed control from Clarity, 2,4-D, Distinct, and Roundup WeatherMax applied at different growth stages; and to determine the minimum interval between application and planting to apply these herbicides without affecting yield.

Studies were initiated in 2004 and repeated in 2005 at the Texas Agricultural Experiment Station near Lubbock and at the AG-CARES research facility near Lamesa, TX. Clarity at 0.125 lb ai/A and 0.25 lb ai/A, Distinct at 0.088 and 0.175 lb ai/A, 2,4-D at 0.50 lb ai/A, and Roundup WeatherMax at 0.75 lb ae/A were applied 4,2, and 1 weeks before planting cotton and at 3, 6, and 12 inches. Weed control ratings were recorded 7, 14, and 21 days after treatment (DAT). Cotton injury ratings were recorded at monthly intervals during the growing season.