Control of Downy Brome (Bromus tectorum) with Herbicides and Perennial Grass Competition

Long-term control of downy brome with an integrated approach is needed in order to sustain range productivity. Studies were conducted to study the effectiveness of a combination of downy brome control practices. In two studies, glyphosate and paraquat were evaluated at various rates for up to three successive years for control of downy brome in rangeland. A third study evaluated the competitiveness of perennial cool-season grasses against downy brome in the absence of herbicides. Glyphosate, at 0.55 kg/ha, and 0.6 kg/ha paraquat provided selective downy brome control on rangeland when applications were combined with intensive grazing. Downy brome control was greater than 90% following two sequential years of 0.6 kg/ha paraquat at either the two- to eight-leaf stage or bloom stage at both study locations. At one study location, 0.55 kg/ha glyphosate provided 97% control after the first application at both growth stages. In the second study, control averaged greater than 92% following three sequential applications of glyphosate. When perennial cool-season grasses were seeded in the spring following fall tillage (no herbicides) and allowed to establish for three growing seasons, three of the five species were effective in reducing the reesta- blishment of downy brome. 'Luna' pubescent wheatgrass, 'Hycrest' crested wheatgrass, 'Sodar' streambank wheatgrass, 'Bozoisky' Russian wildrye, and 'Critana' thickspike wheatgrass controlled 100, 91, 85, 45, and 32% of the downy brome, respectively. Yields of perennial grass dry matter were 1,714, 1,596, 1,135, 900, and 792 kg/ha. Replacing noncompetitive annual grasses with com- petitive cool-season perennials will provide a longer term solution to a downy brome problem than the use of herbicides alone or with intensive grazing. Nomenclature: Glyphosate, N-(phosphonomethyl)glycine; paraquat, 1,1'-dimethyl-4,4'-bipyridinium ion; downy brome, Bromus tectorum L. #3 BROTE; pubescent wheatgrass, Thinopyrum intermedium (Host. Barkworth & Dewey) Nevski 'Luna'; thickspike wheatgrass, Elymus lanceolatus (Scribn. & Smith) Gould 'Critana'; Russian wildrye, Psathyrostachys juncea (Fisch) Nevski 'Bozoisky'; stream- bank wheatgrass, Elymus lanceolatus (Scribn. & J. G. Smith) Gould 'Sodar'; crested wheatgrass, Agropyron cristatum (L.) Gaertn. X (Agropyron desertorum (Gaertn.) 'Hycrest'. Additional index words: Plant competition, rangeland weed control, annual grass control in range- land, cool-season grasses.