By Scout Nelson
European corn borer caterpillars are becoming active in conventional corn fields, making early scouting an important step for producers. The caterpillars feed on young corn leaves while they remain inside the whorl, creating a line of small holes known as shot-hole injury. This feeding damage is often the first visible sign that the pest is present and may require closer inspection.
Adam Varenhorst, Associate Professor and SDSU Extension Field Crop Entomologist, along with Philip Rozeboom and Patrick Wagner, encourage producers to regularly monitor conventional corn because European corn borer populations continue to exist in South Dakota despite the widespread use of Bt corn hybrids. Their observations show that the pest remains active in areas where conventional corn is grown and can still reduce crop productivity if left unmanaged.
European corn borer populations vary across the state. Northern South Dakota typically has one generation each year, while southern areas often experience two generations annually. Current reports of caterpillars feeding in the upper whorl are mainly coming from regions where two generations occur during the growing season.
Proper scouting requires careful field inspections. Producers should examine 20 plants in five different areas of each field, for a total of 100 plants. If shot-hole injury is found, the upper leaves and whorl should be opened to determine how many caterpillars are present and whether they have entered the stalk. This information helps determine whether insecticide treatment is likely to be economically beneficial.
Although Bt corn hybrids successfully manage European corn borer populations, conventional corn remains vulnerable. Without proper management, individual plants may lose between 2% and 6% of their yield. Plants with multiple caterpillars feeding inside the stalk can experience yield losses of up to 12%.
Timing is critical when using insecticides. Treatments are most effective while caterpillars remain inside the whorl before they tunnel into the stalk. Once they move into the stalk, insecticides cannot reach them effectively, making later applications much less successful.
Producers are encouraged to continue scouting fields throughout the season and consult the latest South Dakota Pest Management Guide – Corn for approved insecticides and management recommendations.
Photo Credit: pexels-hong-kimvai
Categories: South Dakota, Crops, Corn