Field-scale spatial distribution, water use, and habitat of wild oat in the semiarid Northern Great Plains

Wild oat (Avena fatua L.) is widely dispersed throughout the Northern Great Plains (NGP), typically occurring in patchy distributions at the field-scale. If weeds are patchy, the environmental impact of weed control and input costs can be reduced through site-specific weed management (SSWM). However, the mechanisms regulating wild oat spatial distribution and the cost effectiveness of SSWM in the NGP need to be understood.; Field experiments were conducted to map wild oat distributions and quantify the accuracy of continuous weed presence/absence maps produced by crop consultants for use in SSWM. The accuracy of wild oat seedling maps was 70%. SSWM of wild oat could be profitable compared to a traditional broadcast herbicide application, even with the associated technology cost and seedling map inaccuracy.; Greater increases in SSWM profitability could be realized if scouting and management efforts were directed to field areas with suitable wild oat habitat. I hypothesized that wild oat habitat may be limited by field-scale heterogeneity in plant available water. The effects of water stress on wild oat growth and fecundity was quantified in a greenhouse experiment. Lower soil matric potentials reduced wild oat relative growth rate and unit leaf rate due to an allometric tradeoff of assimilates from leaf tissue in favor of root tissue, but allowed wild oat to reproduce under adverse climatic conditions. Wild oat was estimated to produce seed above soil matric potentials of −1.66 MPa.; In three grower-managed cereal grain fields, wild oat was seeded in areas with and without historic wild oat patches to delineate field-scale habitat quality. Almost all wild oat habitat-defining variables (leaf area growth rate, harvest biomass, seeds per plant, biomass water use efficiency, and competitive ratio) were similar between existing patch and non-patch areas. Wild oat grew and produced seed regardless of existing patch boundaries and field-scale heterogeneity in soil water use. Wild oat habitat may be unlimited in agroecosystems of the NGP. Future research efforts should focus on limiting weed fecundity and dispersal instead of correlating soil properties to predict wild oat distribution.