University of Illinois

No. 13/June 20, 1997

Western Corn Rootworm Eggs Have Hatched!

John Obermeyer, an entomologist with Purdue University, confirmed recently that corn rootworm eggs have hatched in Indiana. Entomologists at Purdue have used root-staining techniques for many years to spot firstinstar corn rootworm larvae feeding internally within corn roots. Egg hatch this season occurred approximately one day later than last year's delayed egg hatch of June 12. This shouldn't be a surprise, based upon the slow accumulation of soil heat units that we have reported in several earlier issues of this season's Bulletin. The following equation might be worth paying close attention to.

Early Planting + Delayed Corn Rootworm Egg Hatch + Cool, Wet Spring + Extended Larval Feeding Period = Potential Soil-Insecticide Problems

Growers should examine root systems for the presence of corn rootworm larvae later this month and look for any signs of root injury throughout early July. Several soil insecticides are labeled for use as cultivation rescue treatments and include: Counter CR, Dyfonate II 15G, Force 1.5G and 3G, Furadan 4F, Lorsban 15G and 4E, and Thimet 15G and 20G. Cultivation treatments generally perform less satisfactorily than planting-time treatments; however, this season, with corn development lagging and a delayed corn rootworm egg hatch in progress, rescue treatments may be required in some fields.

Mike Gray, Extension Entomologist, (217)333-6652