By Mike Gray, Professor and Extension Entomologist
In spite of the very heavy precipitation and saturated soils in many fields across the state, some western corn rootworm adults have survived and have been sighted in several fields in central Illinois. Matt O’Whene, Research Associate with DuPont Pioneer, observed western corn rootworm adults in a cornfield located in Piatt County on June 24. The western corn rootworm in Matt’s photograph appears to be a male. Males typically emerge first followed by the emergence of females a few days later. By late next week, I expect sightings of western corn rootworm adults to become much more common. It remains to be seen how much root injury will occur this year, especially in areas of the state where resistance to some of the Cry proteins (Cry3Bb1 and mCry3A) has been confirmed. Plants may be more susceptible to lodging this season due to saturated soils, shallow root systems, and frequent storm activity accompanied by windy conditions. As plants become increasingly top heavy, I anticipate more calls related to lodged fields. Don’t automatically assume that lodged fields have root injury associated with rootworm feeding. The only way to confirm corn rootworm larval injury is to dig up plants, wash the soil from the root system, and evaluate the roots for feeding and pruning. We typically wait until mid-July to begin rating roots for injury in our product evaluation trials.
Male western corn rootworm adult, Piatt County, Illinois, June 24, 2015 (Courtesy of Matt O’Whene, Research Associate, DuPont Pioneer).
In addition to observations of western corn rootworm adults in Piatt County, Preston Schrader, Monsanto Company, and Jeremy Lake, Technical Agronomist Asgrow/DeKalb found adults in Macoupin County on June 22. Preston Schrader also indicated adults had been sighted in Menard County. Bottom line — adult emergence is underway and in the coming weeks, it will be time to evaluate the performance of root-protection products (Bt hybrids and/or soil insecticides).