Scout Early for Black Cutworm in Iowa Corn Fields

By Andi Anderson

Iowa corn growers are being urged to scout their emerged fields for black cutworm (BCW) activity this spring. BCW is a migratory pest that arrives each year with spring storms.

Female moths lay eggs in and near crop fields, especially those with cover crops or spring weeds. Once hatched, larvae can damage corn by feeding on leaves or cutting young plants.

The larvae become large enough to cut plants at the 4th instar stage, and this damage can occur until corn reaches the V5 growth stage. Because BCW pressure is unpredictable and varies widely by location, preventive insecticide use is not economical. Instead, effective rescue treatments are recommended if larvae are found during scouting.

This year, BCW moths have been active at trapping sites in several counties including Hamilton, Lucas, Polk, Pottawattamie, Story, and Washington. A significant flight—defined as eight or more moths captured over two nights—triggers growing degree day (GDD) tracking to predict when larvae will reach the 4th instar. Larvae reach cutting size after 300 GDDs from a significant flight.

Based on data from the Iowa Moth Trapping Network and historical GDDs, cutting is predicted to begin soon in several regions. However, delayed trap deployment this year may mean some early flights were missed, especially in southwest and south-central Iowa, so early activity is possible.

Even early-planted corn is still below the V5 stage, meaning it's still vulnerable. Scouting should be combined with early stand assessments. Missing or cut plants are warning signs. Check nearby soil to confirm the presence of BCW larvae.

Monitoring continues across 18 sites in 13 counties. Farmers are encouraged to stay alert and check fields regularly to protect their crops from potential damage.

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