Evaluation of Alternative Planting Strategies to Reduce Wheat Stem Sawfly Damage in Spring Wheat in the Northern Great Plains.

Wheat producers are often reluctant to utilize solid-stemmed wheat cultivars resistant to wheat stem sawfly (WSS) due to concerns regarding yield, efficacy or market opportunities. Several planting strategies were evaluated at two locations over a three-year period using large plots (40 m x 200 m) located adjacent to WSS-infested fields. Planting a solid stand of a resistant cultivar (AC Eatonia) increased yield by an average of 13% (0.4 Mg ha^-1) over the hollow-stemmed cultivar (AC Barrie) and increased the grade of wheat by 1 unit at the two most heavily infested site-years. Planting a 1:1 blend of the resistant and susceptible cultivars increased yield by an average of 11%, while just planting the 20 m or 40 m field margins (trap crop strategy) to AC Eatonia increased yield by an average of 6%. High WSS pressure limited the effectiveness of planting the field margin to a resistant crop because plants were often infested beyond the field margin, with uniform infestation across the whole field at the two most heavily infested site-years. The effectiveness of AC Eatonia to reduce WSS survivorship was modest in this study and likely due to weather-related factors (pith expression) and the fitness and abundance of the WSS population. Utilization of solid stems in monoculture or in a 1:1 blend improved wheat yield and quality over the hollow-stemmed cultivar, but greater benefits with a trap crop strategy would only occur under lower WSS pressure.