Corn Rootworm Heat-Unit Accumulation Update

June 11, 1999
By now you've seen several maps already this season regarding heat-unit accumulations (base 52°F) taken at the 4-inch soil level since January 1 to estimate corn rootworm egg hatch and phenology. Figure 1 provides heat-unit accumulations through June 6 and suggests that egg hatch should be well under way even for northern Illinois counties. Recall that when 380 to 426 heat units have accumulated, as many as 50 percent of the eggs may have already hatched. A comparison of 4-inch soil heat-unit accumulations last year with this year's accumulations suggests we are nearly at the same point as of June 6. By July 10, 1998, we had received numerous reports of corn rootworm adults in cornfields. With the recent very hot weather, don't be surprised if adult emergence begins in late June or very early in July this season. This means we may only be 3 to 3 1/2 weeks away from initial corn rootworm emergence. Get ready: in next week's Bulletin, we'll provide some more information regarding techniques for assessing the performance of soil insecticides and scouting procedures for corn rootworm larvae.--Mike Gray

Author: Mike Gray