We have received a few reports of conventional corn fields being affected by first-generation European corn borer feeding. How do we know that European corn borer was causing the issues? When dissected, the corn stalks had obvious signs of internal feeding, and many of stalks contained a medium-sized brown pupa (Figure 1).
Figure 1. European corn borer pupa inside of a corn stalk. Courtesy: Hunter Welch, South Dakota State University.
For much of South Dakota, European corn borers are capable of having two successful generations. However, in the northern counties of South Dakota, one generation of European corn borers occurs and feeds throughout most of the season. For the areas where two generations are possible, the second generation of adults should be emerging now and becoming active. This indicates that it is also a good time to start scouting conventional corn fields for European corn borer egg masses (Figure 2). These egg masses are located on the underside of corn leaves near the midrib that are right above or below the ear zone.
To scout for egg masses, examine 50 random plants and count the total number of egg masses that are present. Multiply this number by 2 to account for 100 plants. That information is then entered into the European Corn Borer Scouting Tool. If management is necessary, please refer to the 2018 South Dakota Pest Management Guide: Corn for insecticides that are currently labeled for this pest.