Stalk borers can cause stand loss in corn adjacent to grass terraces, waterways, ditches, and fencerows, and especially those areas where stand loss has occurred in previous years. Usually the larvae don't crawl very far from grass, so the problem is often restricted to the first four rows of corn next to grass. The smaller the corn, the more likely it is to be killed by stalk borers. Once corn reaches the 7-leaf stage (V7 stage), stalk borers are unlikely to kill the plants.
|Young stalk borer larva showing purple body with white longitudinal lines.
An exception to the border row problem is when weedy grasses or giant ragweed are growing throughout a cornfield. Giant ragweed is a favorite host for stalk borers so fields with this weed also could have a stalk borer problem. If these weeds are killed, with either a herbicide or cultivation, the stalk borers will move out of the weeds and into the corn. Stalk borers can destroy a corn stand under these circumstances. To prevent this from happening, an insecticide should be tank mixed with the herbicide (if it is a fast burndown herbicide) or the field should be sprayed with the insecticide approximately 7 days after the herbicide (if it is a slow burndown herbicide). Be sure to read the insecticide label before mixing pesticides.
This article originally appeared on page 92 of the IC-494(10) -- May 16, 2005 issue.