Does the accumulation of heat units during the spring affect soil insecticide performance against corn rootworms?
Corn rootworm development is paced by the accumulation of heat units. However, some entomologists have contended that predicting corn rootworm phenology could be accomplished just as effectively with a calendar. Observations during the past several years have led us to believe that corn rootworm egg hatch and root injury are affected profoundly by seasonal temperatures. In 1997, Purdue University entomologists (Pest and Crop Newsletter, no. 13) reported that the corn rootowrm egg hatch was delayed considerably, the latest in 15 years. They attributed the very late hatch to the exceptionally cool spring temperatures. In 1997, heat-unit accumulations (base 52°F, air temperatures) in Monmouth and Urbana were the lowest for the 10-year period being discussed. Under conditions of moderate rainfall, below-average heat accumulations, and intense rootworm pressure, the stage was set for the very poor performance of most soil insecticides at these two locations in 1997.
