Hoary alyssum (Berteroa incana (L.) D.C.) was selectively controlled in alfalfa (Medicago sativa L.) by 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) at 2 lb/A, 3-tert-butyl-5-bromo-6-methyluracil (hereinafter referred to as DuPont 733) at ½ and 1 lb/A, 2,4-dichlorophenoxybutyric acid (2,4-DB) at ½ and 1 lb/A, and by 3-tert-butyl-5-chloro-6-methyluracil (terbacil) at ½ and 1 lb/A. Alfalfa yields were not reduced with consecutive applications for 3 years with the exception that simazine at 2 lb/A caused a significant reduction in first harvest hay yields in the first 2 years. Herbicide applications were made as soon as possible after the last forage harvest in early fall. Treatment at that time destroys the existing photosynthetic area and should reduce the accumulation of carbohydrate reserves in the roots, thereby inhibiting the development of cold hardiness by hoary alyssum plants.