Impact of Environmental and Biological Stressors on the Demography of Multiple Herbicide Resistant Wild Oat (Avena fatua L.).

To address the population dynamics of multiple herbicide resistance (MHR) in a field setting, the objective of these studies were to compare the impacts of stressors on the demography of wild oat (Avena fatua) MHR and herbicide sensitive (HS) biotypes. The first year of a two year study was conducted in Bozeman, MT in 2013 following a split-plot randomized block design with four replications. Whole plots were assigned spring wheat seeded at a density of 67.3 kg ha^-1 (low) or 101 kg ha^-1 (high) and sub-plots were combinations of one of four targeted N levels (56, 112, 168, or 224 kg N ha^-1) and one of three wild oat treatments (HS1, MHR3, or MHR4). In October 2012, wild oat seeds were sown in each sub-plot at a density of 1,000 seeds m^-2. Plots were sprayed with flucarbazone (30 g a.i. ha^-1) at the wild oat 3-leaf stage. In the Fall, wild oat seed production, evaluated prior to wheat harvest, differed among lines (p  < 0.0001) and was negatively affected by N rate (p < 0.02) and seeding density (p < 0.01). HS plants had a high mortality rate due to herbicide application and produced few seeds, and MHR plants produced the lowest number of seeds as nitrogen rate and wheat density increased. Overall, knowledge of the population dynamics of MHR weeds can allow for the design of weed management programs that exploit and manipulate the traits in a weed biotype to reduce infestations.