University of Illinois

No. 18/July 25, 1997

Rootworm Larval Injury: A Major Problem in Many Cornfields

Reports of severe rootworm larval injury, lodged fields, and poor performance of soil insecticides are common this season. Earlier this week, I witnessed the results of the destructive force that rootworm larvae can deliver to a field of corn. The field in question was a first-year cornfield in east-central Illinois that had been treated with a popularly used soil insecticide. In fact, the product has worked very well in our experimental trials, as well as in other university trials across the Midwest. With virtually no difficulty, I found plants that had root systems with two or three nodes of roots completely destroyed. Lodging was equally impressive across this field. Prospects for a satisfactory yield were not encouraging for this producer.

No single soil insecticide has been implicated in the reported failures, and we continue to receive telephone calls from producers regarding the poor root-protection performance of soil insecticides across the board. In short, this season has fulfilled the expectation for soil-insecticide problems as outlined in earlier issues of this Bulletin.

In many fields with severe larval injury, questions regarding potential yield are being "wrestled" with. Hybrids differ considerably in their abilities to compensate for larval injury. Also, in those areas of Illinois that remain dry, rootworm injury is likely to take its greatest toll on potential yield. This season should remain a good reminder that soil insecticides do not always provide satisfactory levels of root protection. If the trend for earlier and earlier planting continues, we should anticipate more soil-insecticide performance problems in the coming years.

Mike Gray, Extension Entomology, (217)333-6652