No. 11 Article 1/June 17, 2010

Despite Saturated Soils, Corn Rootworm Injury Evident in East-Central Illinois

June continues to be a very wet month across Illinois and in many areas of the Corn Belt this year. With all the excess precipitation and standing water in many fields, some have asked how these conditions might affect corn rootworm pressure. Unlike during the previous two growing seasons, I believe this year's rootworm population had a very good chance to establish on root systems and survive because of the early and quick pace of planting this spring. On June 10, Joe Spencer, an entomologist with the Illinois Natural History Survey, confirmed this prediction when he observed severe corn rootworm larval injury on plants in his plots located just north of Urbana. Several nodes of roots had been pruned on many of the plants he examined. More injury is likely because many of the larvae were still second instars, and they will have a chance to continue chewing on additional root tissue as third instars.

Corn rootworm larval injury to plants, June 10, Urbana. (Photo courtesy of Joe Spencer, Illinois Natural History Survey.)

Because of the saturated soils in many areas of the state this spring, I believe root systems may be shallower this year than we would like to see. Shallow root systems and severe root pruning could lead to significant lodging of plants in some fields. In some instances, even without corn rootworm feeding, shallow-rooted plants that become top-heavy later this year could be susceptible to lodging. If lodging occurs later this season, be sure to examine the root systems of these plants and determine the severity of root injury (if any). Don't just assume corn rootworms are responsible.

Emergence is likely just around the corner, and I won't be surprised if I begin to receive some reports of western corn rootworm adults by the end of next week. By the 4th of July, these sightings will become more common.--Mike Gray

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