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Soil Degree-Days and Rootworm Development

May 24, 2002
The words "degree-day accumulations" don't mean much when temperatures are abnormally cool for this time of year. No self-respecting, cold-blooded insect is going to develop much under these conditions. Figure 1 shows actual soil degree-day accumulations (base 52 deg F), at the 4-inch level, from January 1 through May 20, 2002. If you compare this map with the one published as Figure 1 in issue no. 8 (May 17, 2002) of the Bulletin, you won't notice much of a difference. Although we suspect that rootworm larvae have hatched in southern Illinois and have begun hatching in central Illinois, no one has reported finding them yet. (There was one report of a rootworm larva observed doing a prothorax stroke [insect equivalent of a breaststroke] in a ponded field in Champaign County, but the report has not been verified.)

We should begin to learn whether rootworm larvae will have an impact on small corn plants very soon. If the excessive rains have been good for anything, we can at least hope that rootworm larvae have hatched into saturated soils and have died.--Kevin Steffey

Author: Kevin Steffey

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

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