Planting date influence on the wheat stem sawfly (Hymenoptera: Cephidae) in spring wheat

Wasps of the wheat stem sawfly, Cephus cinctus Norton (Hymenoptera: Cephidae), lay eggs in wheat stems, and larval feeding causes lodging and lower yields. Late-planted spring wheat fields avoid attack if stem elongation begins after termination of the annual oviposition period. Moderate delays of 12-20 days in spring wheat planting trials in 7 years resulted in significantly lower infestation levels in 4 years, and complete avoidance of infestation in 3 years. However, delayed spring planting is known to make less efficient use of critical soil moisture, resulting in lower crop yields. Based on our data, safe planting dates for C. cinctus in spring wheat cannot currently he established because of annual variation in the duration of wasp flights, seasonal plant development, and amount of available moisture. We suggest that fields with a history of heavy infestations should be planted last in producers' production program.