A recent Wallaces Farmer article shared that in the last two weeks, soybean fields have been reporting cutworm damage – an unusual phenomenon since cutworm is commonly known as a corn insect pest.
Cutworm damage in corn is reported almost every year in Iowa, Erin Hodgson, an ISU Ext
ension entomologist said, but infestations are patchy and sporadic because the cutworm moths have to migrate into Iowa from the Gulf Coast or from the far southern states such as Texas every spring. The moths are attracted to fields where there are young weed seedlings and the cutworm moths lay eggs in these fields. The eggs hatch to produce the larvae (worms, see image) which chew on corn leaves and can cut off young corn plants.
Cutworm damage in soybeans, however, is not typical. Hodgson says entomologists don’t fully understand why cutworms sometimes cause damage to soybean plants. She said there are a few field conditions that may make soybean fields attractive to female cutworm moths:
- Fields planted under reduced or no-tillage practices
- Fair-to-poorly drained fields
- Fields with winter annual weeds emerged prior to soybean planting
- More likely found in fields previous infested with cutworms
Determining Cutworm Damage
Hodgson recommends checking 20 consecutive plants in five different areas of your field to determine the percent of cutworm damage. Young cutworms may feed on the soybean stem or leaves, but older larvae can clip off cotyledons. Look for discolored, wilted or dead plants. Cutworms will seek shelter during the day, so dig 2-3 inches down in the soil within a row to try to find them. Consider an insecticide if larvae are less than3/4 inch long and more than 20 percent of plants are damaged or missing.
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