Agronomists across the state are opening corn ears for yield and disease assessments and are surprised by western bean cutworm larvae feeding inside. Western bean cutworm is one of several caterpillars found in corn ears this time of year, but people are seeing them more frequently in recent years. Western bean cutworm was historically a common pest that caused economic injury to corn in Iowa in the early 2000s, but sightings have been rare since 2009.
Identification tips: Western bean cutworm is a smooth-skinned caterpillar with a granular appearance. It has a tan head with two dark rectangles behind it. You may see some faint striping down the body, but mature larvae may also look gray or white. Corn earworm, on the other hand, is bumpy and hairy with usually more defined stripes.
Injury: At this time of year, western bean cutworms are causing injury to the ear. Injury is similar to that caused by corn earworm: caterpillars consume kernels and leave frass behind. Unlike corn earworm, multiple caterpillars may be present in a single ear and found anywhere on the ear. Although insecticides are not effective once caterpillars are inside the ear, it is still worthwhile to scout ears for injury to determine whether molds have developed on the ear that may decrease grain quality or be harmful to livestock.
Future management: At this point in the season, no management activities are recommended since well-timed applications rely on scouting for egg masses and making contact with larvae before they enter the ear. However, if you have experienced persistent issues with western bean cutworm in corn, consider choosing hybrids in the future that have the Vip3A trait as this is the only transgenic trait that currently provides adequate suppression of western bean cutworm larvae. Consult the Handy Bt Trait Table for field corn to see which hybrids contain effective traits for western bean cutworm and other target pests.
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