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Issue No. 9, Article 1/June 4, 2010

Few Confirmations of Corn Rootworm Larval Hatch and Inactive Action Sites: A Quiet Spring Thus Far

It continues to be a quiet spring this year with respect to many familiar insects in corn and soybean fields. The morning of June 2 I received some information from Jim Donnelly of Green River Seeds that he observed corn rootworm larvae (about 1 per plant) in the root systems of V7-stage plants in Lee County. The larvae, about 1/8-inch long, were found in refuge corn plants that had not been treated with a soil insecticide at planting.

On June 1, I visited with Joe Spencer, an entomologist with the Illinois Natural History Survey; he has not yet observed any corn rootworm larvae this spring in his research plots. And so far I've not received any confirmation from the entomologists at Purdue University, who are typically the first group to report larval hatch. Yet based on the hot stretch of weather throughout Illinois the last week of May, hatch should be well underway across most of the state. It will be interesting to see whether the western corn rootworm population is present at low levels this season. As I've mentioned previously, wet springs in previous years and the escalating use of Bt hybrids may be pushing densities of this insect to lower levels.

European corn borer action site, Champaign, County, June 1, 2010.

Sweep net contents from action site, Champaign, County, June 1, 2010.

On June 1, I spent some time walking through a dense area of tall grass in Champaign County to see if I could stir up some European corn borer moths. In previous years, especially in the pre-Bt era, it was easy by early June to kick up some moths in action sites such as this. Despite my efforts, I did not observe a single moth, so I took out my sweep net and took approximately 50 sweeps. An examination of the contents revealed no European corn borer moths, only some grasshoppers, spiders, and a few lady beetles. As we move forward through this spring, please let me know if you observe any first-generation European corn borer injury in fields. I would also be interested in other confirmations of the corn rootworm larval hatch that I can share with readers of the Bulletin.--Mike Gray

Mike Gray

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