Soil Heat-Unit Accumulations and Corn Rootworm Egg Hatch: Stay Tuned

May 21, 1999
Observations of lightning bugs have become more numerous during the past week. As many of our readers know, these sightings have been closely linked to the beginning of the annual hatch of corn rootworm eggs. Although these two biological events are not related or linked in any way, they are both temperature dependent.

As indicated in last week's Bulletin, laboratory studies have shown that when 380 to 426 heat units (base 52°F) have accumulated, as many as 50 percent of the eggs are likely to have hatched. Figure 1 reveals that as of May 17, between 200 and 300 heat units (base 52°F, 4-inch soil temperature) had accumulated across central Illinois. As mentioned last week, by May 25, corn rootworm egg hatch should be well under way across most cornfields of central Illinois. Cooler temperatures during the second half of this month may delay the hatch somewhat; however, egg hatch this season is likely to mirror that of last year. We'll keep you posted on this issue for the next several weeks.--Mike Gray

Author: Mike Gray