DIFFERENTIAL COMPETITIVE ABILITY OF WINTER-WHEAT CULTIVARS AGAINST DOWNY BROME

Downy brome (Bromus tectorum L.) causes large yield reductions in winter wheat (Triticum aestivum L.) in the western USA and Canada. Current control practices using fallow and preseeding tillage often are ineffective. A study was conducted over 3 yr at Lethbridge, AB, to determine if winter wheat cultivars varying in height and growth habit differ in their competitive ability with downy brome. A factorial set of treatments included downy brome at 0, 10, 50, and 200 plants m-2 grown with winter wheat cultivars Norstar, Redwin, Archer, and Norwin. Downy brome reduced the biomass and seed yield of all cultivars in all years, but the magnitude of the yield reductions differed among cultivars. Downy brome caused 14 to 30% greater yield reductions in the semidwarf cultivars, Archer and Norwin, than in the tall cultivars, Norstar and Redwin. This differential response among cultivars is partly attributable to competition for light. Norstar and Redwin shaded downy brome for much of the growing season, but Archer and Norwin often were shaded by downy brome. Planting a more competitive cultivar of winter wheat results in higher crop yields and less downy brome seed for weed establishment in subsequent crops. Use of competitive winter wheat cultivars should be a component of integrated weed management systems for downy brome.