No. 10 Article 5/June 1, 2007

European Corn Borer Moths Statewide

We have received several reports of observations of European corn borer moths (either in traps or in "action sites" where moths congregate) from southern, western, and northern Illinois counties. As corn continues to grow rapidly, the moths will be attracted to the tallest corn fields in an area for oviposition. The earliest planted fields generally are most at risk from injury caused by first-generation European corn borers, but when many corn acres in an area were planted at approximately the same time, corn borers likely will be dispersed over lots of acres, possibly reducing the threat in any given field. Nonetheless, monitoring for signs of European corn borer infestations is appropriate from now (in southern and western Illinois) through mid-June.

So much information about European corn borer is available on the Internet that it seems impractical to repeat much that has been written. Instead we direct your attention to a couple of good sources of information. You can access our fact sheet on European corn borers on-line. A more fully developed publication, European Corn Borer Ecology and Management (North Central Regional Extension Publication No. 327, 1996), is also accessible on the Internet. Of particular interest at this time of year is accumulation of degree-days to keep track of European corn borer development. Table 1 of European Corn Borer Ecology and Management shows accumulated degree-days from initial captures of moths in the spring for first occurrence of life stages. You can get to the table from the main page by clicking on "The Insect," then on "Life Cycle and Generational Ecotypes"; scroll down to Table 1.

It seems patently obvious that non-Bt cornfields should be scouted for injury caused by early instar European corn borers, but don't forget to scout non-Bt corn refuges associated with Bt corn fields. The guidelines for insect resistance management for Bt corn allow for application of an insecticide, if necessary, to control corn borer larvae in the non-Bt corn refuge. And it's probably not a bad idea to look occasionally for evidence of corn borer injury in Bt corn, too. Although there is no suggestion that European corn borers have developed resistance to the Bt protein expressed in Bt corn plants in the field, lab studies have indicated that such resistance is possible. No insect control technique is infallible.--Kevin Steffey

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