Control of wild oat in the year of smooth bromegrass establishment and its effect on the yield and quality of subsequent seed crops

Wild oat (Avena fatua L.) control from three graminicides, clodinafop-propargyl, fenoxaprop-p-ethyl and tralkoxydim, in seedling stands of smooth bromegrass (Bromus inermis L.) seeded alone or with spring wheat (Triticum aestivum L.) was studied in 1991, 1992 and 1993 at Beaverlodge, Alberta. Seed yield and quality were measured for 2 yr after each year of establishment. In the year of establishment, clodinafop-propargyl at 60 g ha–1 consistently provided ≥80% visual control of wild oat growing in smooth bromegrass seeded with wheat, while the mean probability of similar applications of fenoxaprop-p-ethyl at 92 g ha−1 and tralkoxydim at 250 g ha−1 to provide ≥80% visual control of wild oat, averaged over the years of establishment, was 0.91 and 0.92, respectively. Without the wheat companion crop, the mean probability of clodinafop-propargyl to provide ≥80% visual control of wild oat, averaged over establishment years, remained above 0.90, but that for fenoxaprop-p-ethyl and tralkoxydim was reduced to 0.36 and 0.50, respectively. The efficacy of the three graminicides to control wild oat was reduced by tank mixing with bromoxynil plus MCPA, thifensulfuron methyl plus MCPA, or MCPA alone. Establishment with wheat had a major detrimental impact on smooth bromegrass seed yields harvested 1 and 2 yr after each establishment year. Smooth bromegrass seed yields harvested 1 yr following the year of establishment were three times greater where smooth bromegrass was seeded alone as compared with being seeded with wheat. Seed yields harvested 2 yr after the year of establishment followed a similar trend, but the differences were smaller. Herbicide treatments had no effect on either first or second smooth bromegrass seed yields. Wild oat dockage was present only in the first smooth bromegrass seed crop and was approximately three times greater following establishment with wheat than following establishment alone. Percent wild oat dockage was less from plots where herbicides had been applied than from weedy check plots. Differences in percent dockage occurred among herbicide treatments but were small. Key words: Smooth bromegrass, Bromus inermis, wild oat, Avena fatua, graminicides, tank mixtures