Improving kochia (Kochia scoparia L.) and wild oat (Avena fatua L.) management in cultivated oat (Avena sativa L.)

Saskatchewan is the largest producer of oat (Avena sativa L.) in Canada, producing 54% of Canadian oats. Weeds such as kochia (Kochia scoparia L.) and wild oat (Avena fatua L.) are problematic in oat and require improved chemical and cultural control practices. The objectives of this thesis were two-fold: 1) to determine the tolerance of oat to pre- and post-emergence herbicides and their efficacy for controlling kochia (field study), and 2) to determine the relative effect of seed size and seed treatment on oat competitive ability (greenhouse and phytotron studies). In the field study, fluthiacet-methyl, flumioxazin, florasulam + bromoxynil, acifluorfen, and topramezone were applied POST, while tembotrione and sulfentrazone were applied PRE, to evaluate kochia control and oat tolerance. Pyrasulfotole+ bromoxynil, flumioxazin, tembotrione, and fluthiacet-methyl provided excellent kochia control (>88% biomass reductions). Oat tolerance to pyrasulfotole+ bromoxynil and fluthiacet-methyl was commercially acceptable. In the greenhouse and phytotron studies, two seed sizes (large and small), four seed treatments (pyraclostrobin, pyraclostrobin + thiamethoxam, thiamethoxam, control) and two competitive environments (weed-free and weedy) were evaluated. Under cool growing conditions, seed treatments lead to an increase in shoot production up to 15 and 18%, respectively, for both large and small seeds. Oat plants derived from large seeds produced 23 and 24% more root and shoot biomass, respectively, compared to plants established from small seeds at early developmental stages. The seed size advantage persisted until physiological maturity as plants established from large seeds produced 38% more shoot biomass and 12% more panicles than oat plants derived from small seeds. Regardless of seed size, oat plants produced 78% less shoot biomass and 32% fewer panicles when wild oat competition was present compared with no pots having no wild oat competition. Results presented in this thesis show that pyrasulfotole+ bromoxynil and fluthiacet-methyl are potential herbicides for control of kochia in oat, as they provided excellent control and acceptable crop tolerance. In addition to chemical control, oat producers should consider the use of seed treatments and large seed to improve early season oat vigour and competitive ability