No. 12 Article 3/June 12, 2009

European Corn Borer Moths and Larvae Active

On June 5, I observed European corn borer moths in grassy ditch banks (action sites) surrounding fields in Champaign and Piatt counties. The moths were not very numerous, and most of the corn plants in nearby fields were still very small seedlings--from a European corn borer's perspective, a target site less than ideal for laying eggs. Last fall, our annual corn borer survey revealed historically low levels of this once-prominent insect pest. The delays in planting this spring will contribute to poor survivorship of the first generation. Add to this scenario the escalating use of highly effective Bt hybrids and we should anticipate first-generation corn borer infestations being relatively scarce this year across much of the state.

Further to the south, Dr. Doug Johnson, an extension entomologist at the University of Kentucky Research and Educator Center in Princeton, Kentucky, reported that economic levels of European corn borer had been confirmed in one non-Bt cornfield. However, he also reported that overall numbers of European corn borers caught in traps were very low. Mike Roegge, extension crop systems educator, Adams/Brown Extension unit, reported moths as well as first-instar European corn borers in a field of sweet corn.

Historically, late planting of corn has favored the establishment of second-generation European corn borer infestations. Although I anticipate very low densities of European corn borers this season, refuges of non-Bt corn could be vulnerable to significant infestations late in the growing season--from an insect resistance management perspective, not a bad thing. Recall that the aim of refuge implementation is to prolong the usefulness of Bt hybrids by preventing or delaying resistance development. To accomplish this goal, European corn borer survivors are needed in refuges to increase the chance that any rare resistant European corn borer that survives after feeding on a Bt corn plant will mate with a susceptible moth. I encourage growers to scout both Bt and refuge areas of fields and to report any unusual or unanticipated signs of insect injury to Bt plants.--Mike Gray

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