Efficacy of Propoxycarbazone-sodium for Cheat (Bromus secalinus) Control in Winter Wheat and Carryover on Double-Cropped Grain Sorghum

Southern Great Plains wheat growers typically apply either sulfosulfuron or propoxycarbazone-sodium for selective control of cheat. Although astute growers apply herbicides early in the growing season, herbicide application is often delayed until mid-winter or later. The effects of application timing of propoxycarbazone-sodium on cheat efficacy and on injury to the following grain sorghum crop have not been documented. Application of each herbicide at 17 intervals throughout the growing season indicated that cheat control with propoxycarbazone-sodium was greater than or equal to 90% even when application was delayed for several months after seeding. In contrast, cheat control with sulfosulfuron was variable when application was delayed more than 6 wk after wheat was seeded. Delaying sulfosulfuron application decreased wheat yield. Grain sorghum was not affected by propoxycarbazone-sodium residues regardless of application timing to wheat. Conversely, grain sorghum was severely injured by sulfosulfuron residues regardless of herbicide application timing. Nomenclature: Propoxycarbazone-sodium; sulfosulfuron; cheat, Bromus secalinus L. BROSE; grain sorghum, Sorghum bicolor L.; wheat, Triticum aestivium L.