FALLOW METHOD AFFECTS DOWNY BROME POPULATION IN WINTER-WHEAT

Downy brome (Bromus tectorum L.) is a prevalent weed in. festing winter wheat (Triticum aestivum L.) in the Great Plains. Long-term field research was initiated in 1980 on a Williams loam soil (fine-loamy, mixed Typic Argiborolls) near Sidney, MT, to determine the effect of stubble mulch (SM), minimum-till (MT), and no-till (NT) fallow methods on downy brome proliferation in winter wheat-fallow cropping systems. In 1981, downy brome was not observed in the plot area. By 1989, downy brome comprised 32% of the winter wheat community phytomass in the SM method, but was not detected in winter wheat of the MT or NT methods. Winter wheat grain yield in 1989 was 23 and 29% less in the SM method infested with downy brome than in the MT or NT methods, respectively. Pronamide eliminated downy brome during the fallow period in the MT and NT methods, and thus reduced downy brome population in the following winter wheat crop.