Integrating the Building Blocks of Agronomy Into An IPM Strategy for Wheat Stem Sawfly.

The wheat stem sawfly (Cephus cinctus Norton [Hymenoptera: Cephidae]) is a serious threat to wheat (Triticum aestivum L.) and other cereal grains in the Northern Great Plains. Insecticides have proven ineffective for sawfly control; furthermore, insecticides can be detrimental to beneficial insects. The management of C. cinctus, therefore, requires the integration of crop breeding, agronomy, entomology, and biocontrol. Three experiments were initiated to assess the response of C. cinctus and natural enemies of wheat stem sawfly to the following crop management strategies: cultivar selection, residue management, seeding rates, nitrogen and micronutrient management, and harvest management tactics. Solid-stemmed cultivars were usually agronomically superior to susceptible cultivars when sawflies were present. The stubble disturbance associated with residue management and direct seeding in a continuous cropping regime reduced sawfly populations compared to a wheat-fallow system.  Increased seeding rates can optimize yield, but an inverse, negative relationship between pith expression (stem solidness) and higher seeding rates was observed.  Positive yield responses were observed with N rates > 30 kg N ha-1, but increased stem cutting occurred with higher N rates.  Micronutrient applications did not enhance stem solidness.  Increased cutting heights conserved natural enemies and chopping straw for improved residue management did not affect wheat stem sawfly parasitoids that overwinter in the straw. In summary, an agronomic strategy to manage wheat stem sawfly consists of solid-stemmed cultivars, appropriate pre-seed residue management, seeding rates no greater than 300 seeds m^-2, 30 to 40 kg N ha^-1, and harvest cutting heights of at least 15 cm.