University of Illinois

No. 12/June 12, 1998

European Corn Borer Update:
Don't Delay Scouting Efforts

European corn borer moths have been common throughout the state for about 3 weeks. Producers in central and northern Illinois should have started their scouting efforts already for the first generation of this insect pest. If not, they should begin in earnest. Heat-unit totals (base 50 degrees F) from the first significant moth flight (about mid-May) suggest that corn borer larvae by June 8 were between the second- and third-larval instar stage. Figure 1 provided by Bob Scott, Illinois State Water Survey, gives the heat-unit totals(base 50 degrees F) from January 1 to June 8. By referring to previous issues of this Bulletin, you can keep track of how many heat units have accrued on a week-by-week basis. Also, by referring to Table 2 of last week's Bulletin (no. 11, page 112 in the print version), you can estimate the stage and general activity of corn borers in your area of the state.

Figure 1. Actual heat-unit accumulation (base 50 degrees F), January 1 to June 8, 1998.

Heat-unit totals through June 8 indicate that stalk tunneling has been under way for some time in southern Illinois, and many fields will not benefit from an insecticide application. Let us know what your scouting efforts for European corn borer reveal.

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