Corn Rootworm Larval Injury and Adult Emergence Lagging this Season

Although western corn rootworm adult emergence is underway across many central Illinois counties, a quick poll of participants at the DeKalb Research and Education Center field day near Shabbona, Illinois on July 10 revealed that participants have not observed any beetles moving about their cornfields. Joe Spencer, an entomologist with the Illinois Natural History Survey, observed larvae continuing their root feeding activity in his research plots north of Urbana on July 9. Based upon these observations, the beginning of our annual root injury evaluations led by Ron Estes, Principal Research Specialist, Department of Crop Sciences, will be delayed about 1 week from our typical mid-July time frame. Reasons for the delayed feeding and emergence this season likely relate to the deeper egg laying during last year’s drought and the heavy precipitation this spring and early summer across much of Illinois. Saturated soils do not warm up as rapidly as dry soils and heat unit accumulations, key to the timing of corn rootworm development, have not accrued as fast this growing season. Joe Spencer also noted lodging in his research plots following some heavy rains and wind that moved through portions of east central Illinois on July 10. On July 17, a field day is scheduled for the Northwestern Research and Education Center near Monmouth, Illinois. Producers are encouraged to bring 10 roots from their fields for root injury evaluations. I will have a crew on site to assist with the evaluations and answer any questions.

Mike Gray