Growers should begin scouting their emerging corn seedlings for signs of leaf feeding and cutting by black cutworms, according to coordinator of the Illinois Cooperative Agricultural Pest Survey Kelly Estes. Significant moth flights in late March and early April could have caused a significant presence of cutting-stage larvae in many areas of the state in the coming weeks.
Potential cutting dates are determined by using the reports of intense captures (nine or more moths in a one- to two-night trapping period) and calculating degree-day accumulations using historical temperature data. We can expect fourth instar larvae to be present after the accumulation of 300 degree-days.
Early (first through third) instar feeding appears as pinhole injury on leaves. By the time the larvae become fourth instars, they begin cutting plants off and dragging them into their burrows to feed. As the larvae grow through their sixth or seventh instars (the number depends on diet and temperature), they require increasingly more food, so the larger larvae may cut off several corn seedlings. Depending on temperature, larvae develop over 28 to 35 days.
Estes recommends scouting the cornfields for black cutworm injury and welcomes reports from farmers about their observations.