Integrated Crop Management is published by the Department of Entomology , Iowa State University , Ames, Iowa. European corn borers are flying across the state and laying eggs, especially on taller corn. Here is an overview of first-generation European corn borer damage, scouting suggestions, economic thresholds, and possible insecticides for control. It really varies by hybrid and environmental stress. This yield loss can be multiplied by the number of corn borers per plant up to 6 larvae per plant, so yield loss can be severe with large infestations.
Young larvae crawl deep inside the whorl after hatching and eat small holes in the leaves.
Shotholes indicate that larvae were feeding inside the whorl, although they may have since died or moved to a different plant. The moths are most attracted to the tallest corn, so begin here. Begin looking for shotholes in the leaves after corn reaches 17-21 inches in extended leaf height. When shotholes or larvae are found in the taller corn, then scout fields with smaller corn. Walk at least 100 feet in from the field edge.