Evaluation of alternative planting strategies to reduce wheat stem sawfly (Hymenoptera: Cephidae) damage to spring wheat in the northern Great Plains.

Wheat, Triticum aestivum L., producers are often reluctant to use solid-stemmed wheat cultivars resistant to wheat stem sawfly, Cephus cinctus Norton (Hymenoptera: Cephidae), due to concerns regarding yield, efficacy or market opportunities. We evaluated the impact of several planting strategies on wheat yield and quality and wheat stem sawfly infestation at two locations over a three-year period. Experimental units consisted of large plots (50 by 200 m) located on commercial farms adjacent to wheat stem sawfly-infested fields. Compared with a monoculture of a hollow-stemmed cultivar ('AC Barrie'), planting a monoculture of a solid-stemmed cultivar ('AC Eatonia') increased yield by an average of 16% (0.4 mg ha(-1)) and increased the grade of wheat by one unit at the two most heavily infested site-years. Planting a 1:1 blend of AC Eatonia and AC Barrie increased yield by an average of 11%, whereas planting 20- or 40-m plot margins to AC Eatonia increased yield by an average of 8%. High wheat stem sawfly pressure limited the effectiveness of using resistant cultivars in field margins because plants were often infested beyond the plot margin, with uniform infestation down the length of the plots at the two most heavily infested site-years. The effectiveness of AC Eatonia to reduce wheat stem sawfly survivorship was modest in this study, probably due to weather-related factors influencing pith expression and to the high abundance of wheat stem sawfly. Greater benefits from planting field margins to resistant cultivars or planting a blend of resistant and susceptible cultivars might be achievable under lower wheat stem sawfly pressure.