One of the most important insect pests of corn will be upon us within a few weeks. We have received one unconfirmed report of captures of European corn borer moths in cone traps in southern Illinois during the first week of May. Finding corn borer adults this early in the season in southern counties is not unprecedented. Spring development of the European corn borer begins when temperatures exceed 50°F. As soon as temperatures warm up in the spring, overwintering corn borer larvae break their diapause ("hibernation") and pupate. The pupal stage lasts for about a week before adults emerge.|
Tracking the development of European corn borers can be accomplished by accumulating heat units above a base temperature of 50°F. However, instead of accumulating heat units from January 1, entomologists suggest that you begin recording accumulating heat units after the first spring moth is observed. First instars hatch from eggs when approximately 212 heat units have accumulated, and second instars may be apparent when approximately 318 heat units have accumulated. The critical third instars may be found when approximately 435 heat units have accumulated. You will find first instars in whorl leaves approximately 2 weeks after you observe the first spring moths.
Obviously, corn borers that emerge this early must find suitable corn plants on which to lay their eggs. If corn is less than 16 inches tall when the females deposit their eggs, survival of young larvae will be poor. Consequently, early planted fields are most at risk. Early planted fields in southern counties should be scouted soon for signs of European corn borer activity. Stay tuned for further developments.--Kevin Steffey