Heat-Unit Accumulations for Corn Rootworm Egg Hatch

May 14, 1999
Can we expect corn rootworm eggs to begin hatching at a "normal" point in time this spring? Many of you recall that corn rootworm egg hatch was considerably delayed (mid-June) in 1997. Last year, corn rootworm eggs began to hatch in late May and early June.

This time frame is considered more typical. Western and northern corn rootworm eggs have a developmental threshold of 52°F. About 380 to 426 degree-day accumulations are required for 50 percent of the eggs to hatch. Figure 2 depicts the soil heat units (base 52°F) that have accumulated at the 4-inch level from January 1 through May 9. For central Illinois, about 280 heat units are still required before 50 percent of the eggs should be expected to have hatched. If we experience average daily temperatures of 70°F for the next 2 weeks, we should not be surprised to see roughly 50 percent of the rootworm eggs beginning to hatch by May 25. This year's hatch will closely resemble last year's. We'll keep you posted as the heat units accumulate, and we'll try to pinpoint precisely when rootworm injury should begin to show up in your fields. As always, stay tuned.--Mike Gray

Author: Mike Gray