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

Wild oat (Avena fatua L.) control from three graminicides, clodinafop-propa rgyl, fenoxaprop-p-ethyl and tralkoxydim, in seedling stands of smooth brom egrass (Bromus inermis L.) seeded alone or with spring wheat (Triticum aest ivum L.) was studied in 1991, 1992 and 1993 at Beaverlodge, Alberta. Seed y ield and quality were measured for 2 yr after each year of establishment. I n the year of establishment, clodinafop-propargyl at 60 g ha(-1) consistent ly provided greater than or equal to 80% visual control of wild oat growing in smooth bromegrass seeded with wheat, while the mean probability of simi lar applications of fenoxaprop-p-ethyl at 92 g ha(-1) and tralkoxydim at 25 0 g ha(-1) to provide greater than or equal to 80% visual control of wild o at, averaged over the years of establishment, was 0.91 and 0.92, respective ly. Without the wheat companion crop, the mean probability of clodinafop-pr opargyl to provide greater than or equal to 80% visual control of wild oat, averaged over establishment years, remained above 0.90, but that for fenox aprop-p-ethyl and tralkoxydim was reduced to 0.36 and 0.50, respectively, T he efficacy of the three graminicides to control wild oat was reduced by ta nk mixing with bromoxynil plus MCPA, thifensulfuron methyl plus MCPA, or MC PA 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 establi shment were three times greater where smooth bromegrass was seeded alone as compared with being seeded with wheat. Seed yields harvested 2 yr after th e year of establishment followed a similar trend, but the differences were smaller. Herbicide treatments had no effect on either first or second smoot h bromegrass seed yields. Wild oat dockage was present only in the first sm ooth bromegrass seed crop and was approximately three times greater followi ng establishment with wheat than following establishment alone. Percent wil d oat dockage was less from plots where herbicides had been applied than fr om weedy check plots. Differences in percent dockage occurred among herbici de treatments but were small.