Chairperson, Graduate Committee: Fabian D. Menalled and Tim F. Seipel (co-chair)Wong, Mei-Ling2022-03-292022-03-292021https://scholarworks.montana.edu/handle/1/16317Wild oat (Avena fatua L.) is one of the most difficult weeds to manage in spring cereal crops and causes large economic losses throughout the Northern Great Plains. The continual use of herbicides for wild oat management has selected for herbicide resistant and multiple herbicide resistant biotypes and has left no selective herbicide options for farmers in small-grain fields. To sustain crop production, this thesis aimed to develop ecologically based practices to manage wild oat populations. We evaluated the impact of spring wheat height, seeding rate, crop type, forage termination method, and tillage on wild oat tiller density, biomass, and seed production. Two studies were conducted: (1) from 2017 through 2019 in Bozeman, Montana and (2) from 2018 through 2019 in Moccasin, Montana. The first study examined the combined effect of spring wheat height and seeding rate on its competitiveness against wild oat. We found that the tall near-isogenic wheat line did not have greater wild oat suppression than the short line. Spring wheat seeded at a higher than recommended rate reduced wild oat biomass and seed production only when nitrogen fertilizer was applied. The second study assessed management practices including integrating lentil, fall and spring forage mixture, sheep grazing and tilled fallow, in addition to spring wheat height and seeding rate. Forage mixtures, sheep grazing, and tillage were the most successful tactics in suppressing wild oat growth and seed production. However, wild oat suppression was not different between spring wheat and lentil, regardless of spring wheat height and seeding rate. Our results indicate that spring wheat height was not correlated with increased suppression of wild oat. A higher seeding rate of spring wheat also did not increase wild oat suppression; we suggest that fertilization may be needed to enhance crop competitiveness. Integrating forage crops with sheep grazing has the best potential to reduce the wild oat seed bank. This information can help redesign cropping systems. However, there is a continual need to develop other integrated weed management techniques to limit wild oat growth and seed production and to reduce reliance on herbicides.enWild oatHerbicide resistanceCrop diversificationForage plantsGrazingWheatFertilizersThesisCopyright 2021 by Mei-Ling Wong