DOWNY BROME (BROMUS-TECTORUM), JOINTED GOATGRASS (AEGILOPS-CYLINDRICA) AND HORSEWEED (CONYZA-CANADENSIS) CONTROL IN FALLOW

Jointed goatgrass, downy brome, and horseweed are increasingly trouble some winter annual weeds during fallow periods in conservation-tillage systems in the southern Great Plains. These experiments determined th e optimum weed size, vigor, and minimum herbicide rate required for 95 % or better control of these weeds on fallow land. Jointed goatgrass a nd downy brome were controlled best when plants were 10 cm or less tal l and growing vigorously at time of treatment. Horseweed was controlle d best when plants were 30 cm tall and growing vigorously. Based on lo cal retail and application costs and assuming optimum conditions for c ontrol, the two most economical herbicide treatments that controlled e ach weed 95% or better were: jointed goatgrass, clethodim at 250 g ai/ ha and glyphosate + 2,4-D at 249 + 479 g ae/ha; downy brome, quizalofo p at 18 g ai/ha and glyphosate + 2,4-D at 582 + 950 g ae/ha; and horse weed, 2,4-D at 560 g ae/ha and metsulfuron at 5 g ai/ha. Nomenclature: Clethodim, 2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one; glyphos ate, N-(phosphonomethyl)glycine; metsulfuron, 2-[[[[4-methoxy-6-methyl -1, triazin-2-yl)amino]carbonyl]amino]sulfonyl]benzoic acid; quizalofo p, [4-[(6-chloro-2-quinoxalinyl)oxy]phenoxy]propanoic acid; 2,4-D, (2, 4-dichlorophenoxy)acetic acid; downy brome, Bromus tectorum L. #(3) BR OTE; horseweed, Conyza canadensis (L.) Croq. # ERICA; jointed goatgras s, Aegilops cylindrica Host # AEGCY.