By Scout Nelson
Western bean cutworm caterpillars have recently been reported in South Dakota corn fields. This marks the first known case of these pests affecting corn with the Cry1F protein in the state.
Reports come at a time when experts have already noted declining effectiveness of Cry1F in controlling western bean cutworms in nearby states. Because of this, Cry1F is no longer recommended for management. Instead, the VIP3A Bt protein or well-timed foliar insecticide applications are considered reliable control options.
Western bean cutworms are a concern because they feed on tassels, silks, and corn ears. Their feeding activity not only reduces yields but also increases the risk of secondary diseases and mold.
Most years, these pests are not commonly seen in South Dakota. However, this year’s reports involve late-stage caterpillars actively feeding on corn ears. Research from Iowa and Nebraska shows that even one caterpillar per ear can reduce yields by about four bushels per acre.
For insecticide control, timing is key. Effective management must happen when egg masses are detected on whorls or upper leaves. Since this season’s reports involve caterpillars already well developed, it is too late for effective insecticide treatments.
Farmers are encouraged to scout fields regularly and pay attention to insect stages. Identifying western bean cutworm moths and caterpillars is important. The moths are gray to brown, with a light stripe along the edge of the front wings.
They also have a distinct brown circle and a comma-shaped marking outlined in lighter color. Caterpillars change colour as they grow. Newly hatched larvae have black heads that later turn orange.
Photo Credit: gettyimages-luc-pouliot
Categories: South Dakota, Crops, Corn