TILLAGE AND ROTATION INFLUENCES ON WEED COMMUNITY COMPOSITION IN WHEAT (TRITICUM-AESTIVUM-L) IN SOUTHWESTERN SASKATCHEWAN

The effects on weed community composition of zero-, minimum-, and conventional tillage practices were examined on three soil types under both continuous wheat (Triticum aestivum L.) and wheat-fallow rotations between 1982 and 1989. Green foxtail [Setaria viridis (L.) Beauv.] became a problem on continuously cropped plots, especially on the sandy loam soil where densities reached a maximum of 2354 plants m-2 with conventional tillage. Without tillage, high densities of foxtail barley (Hordeum jubatum L.) developed since this species was not adequately controlled by herbicides. Even in a year when precipitation was only 63% of normal, perennial shoots of this species achieved a maximum density of 1222 plants m-2. A hoe seeder tended to improve foxtail barley control relative to the disc seeder used, likely due to greater soil disturbance. Wheat losses were significantly correlated to weed density, and it was concluded that, in terms of weed control in wheat, some degree of tillage may be required in southwestern Saskatchewan.