The inherent genetic similarity between oat (<i>Avena sativa</i> L.) and wild oat (<i>Avena fatua</i> L.) precludes selective herbicide use to control wild oat. Consequently, large reductions in oat yield and quality due to wild oat consistently constrain oat production in western Canada. Traditionally, delayed seeding followed by tillage prior to planting was used to control wild oat, but new studies have shown that this practice also results in substantial reductions to oat yield and quality. Thus, new methods are needed to ameliorate the adverse effects of wild oat competition on oat. Planting more competitive varieties with earlier emergence and larger seeds may minimize losses associated with wild oat competition. Therefore, the objectives of this research were i) to determine the influence of wild oat emerging at different times and varying densities on oat yield and quality and ii) to determine the relative importance of seed size and genotype in affecting wild oat oat competition. High densities of early emerging wild oat greatly reduced oat yield and increased wild oat contamination. Observed oat yield losses were as great as 70% and resulted in a 15% wild oat contamination level. Wild oat that emerged before oat also had higher biomass and reproductive output than wild oat that emerged after oat. Furthermore, early emerging wild oat reduced percentage plump oat kernels and increased percentage thin kernels. Oat plants established from large caryopses produced 18% more biomass and 15% more panicles m^-2 than plants established from small caryopses. In addition, wild oat produced 31% less biomass and fewer panicles m^-2 when grown with oat plants established from large caryopses. CDC Boyer appeared to be the most competitive of the varieties examined, having significantly higher biomass and panicle production both in the presence and absence of wild oat competition. Conclusions that emerge from this research are i) emergence time is critical to wild oat oat competition, ii) it is essential for oat producers to control early emerging wild oat and ensure crop emergence precedes wild oat emergence, iii) planting large seed of competitive cultivars may improve the competitive response of oat to wild oat.

The inherent genetic similarity between oat (<i>Avena sativa</i> L.) and wild oat (<i>Avena fatua</i> L.) precludes selective herbicide use to control wild oat. Consequently, large reductions in oat yield and quality due to wild oat consistently constrain oat production in western Canada. Traditionally, delayed seeding followed by tillage prior to planting was used to control wild oat, but new studies have shown that this practice also results in substantial reductions to oat yield and quality. Thus, new methods are needed to ameliorate the adverse effects of wild oat competition on oat. Planting more competitive varieties with earlier emergence and larger seeds may minimize losses associated with wild oat competition. Therefore, the objectives of this research were i) to determine the influence of wild oat emerging at different times and varying densities on oat yield and quality and ii) to determine the relative importance of seed size and genotype in affecting wild oat oat competition. High densities of early emerging wild oat greatly reduced oat yield and increased wild oat contamination. Observed oat yield losses were as great as 70% and resulted in a 15% wild oat contamination level. Wild oat that emerged before oat also had higher biomass and reproductive output than wild oat that emerged after oat. Furthermore, early emerging wild oat reduced percentage plump oat kernels and increased percentage thin kernels. Oat plants established from large caryopses produced 18% more biomass and 15% more panicles m^-2 than plants established from small caryopses. In addition, wild oat produced 31% less biomass and fewer panicles m^-2 when grown with oat plants established from large caryopses. CDC Boyer appeared to be the most competitive of the varieties examined, having significantly higher biomass and panicle production both in the presence and absence of wild oat competition. Conclusions that emerge from this research are i) emergence time is critical to wild oat oat competition, ii) it is essential for oat producers to control early emerging wild oat and ensure crop emergence precedes wild oat emergence, iii) planting large seed of competitive cultivars may improve the competitive response of oat to wild oat.