Downy Brome Competition and Control in Dryland Wheat1

Abstract

AbstractCompetition between downy brome (Bromus tectorum) and winter wheat causes serious economic losses to growers in the Pacific northwest. On a site which received 25 cm average annual rainfall and had a light soil (very fine sandy loam) winter wheat yields were reduced 28% by fewer than 54 downy brome plants per m2 (5 plants/ft2). On a site which received 55 cm average annual precipitation and had a silt loam soil, winter wheat yields were reduced 92% by more than 538 downy brome plants per m2 (50 plants/ft2). Downy brome seed‐to‐straw ratios were indicative of a tremendous yield potential. Seed‐straw ratios of 1:4 are probably an exception but ratios of 1:1 and 1:2 were common.Chemical fallow studies at three sites showed that nonselective downy brome control can be obtained by the use of herbicide combinations such as 3‐amino‐l‐2, 4‐triazole‐ammonium thiocyanate (amitrole‐T), plus chloro‐4‐ethylamino‐6‐isopropylamino‐s‐triazine (atrazine) or amitrole‐T plus 2,4‐dichlorophenoxyacetic acid (2,4‐D). Amitrole‐T plus atrazine was more effective when used as a fall treatment. Amitrole‐T plus 2,4‐D was more effective in the spring. These chemicals reduced tillage requirements and decreased downy brome growth by 90%.