To receive weekly email notification when the latest issue of the Bulletin is online, click on this link and fill out the form.

Corn Rootworm Larval Hatch Anticipated

June 7, 2002
As some of our readers may recall, the corn rootworm larval hatch was very early in 2001. Larry Bledsoe, an entomologist with Purdue University, found corn rootworm larvae in central Indiana on May 16 last year, the earliest confirmed hatch since 1985. Western corn rootworm eggs have a developmental threshold of 52 deg F. About 380 to 426 degree-day accumulations are required for 50 percent of the larvae to hatch. Robert Scott, Illinois State Water Survey, has provided us with a map (Figure 5) that depicts soil heat-unit (base 52 deg F) accumulations at the 4-inch level from January 1 through June 3, 2002. According to this map, we should expect that approximately 50 percent of corn rootworm larvae have hatched in roughly the southern half of the state. Due to the excessive precipitation in May and subsequent planting delays, corn rootworm larvae may hatch into fields with very small root systems. In east-central Illinois, severe root injury may result in many of these first-year cornfields. Many growers may recall that western corn rootworm densities were very large in east-central Illinois soybean fields during the 2001 season. Soil insecticide applications should prevent excessive injury; however, producers should still examine plants for signs of root injury. Comparing root injury levels between treated and check strips should allow producers to begin evaluating the value of their chosen soil insecticide. We'll keep you updated on the evolving rootworm story as the season develops.--Mike Gray

Author: Mike Gray

The Pest Management and Crop Development Bulletin
Executive Editor: Kevin Steffey, Extension Entomologist

Subscription information: Phone (217) 244-5166 or email
Comments or questions regarding this web site: