Black cutworms can cause significant setbacks for corn growers if not identified and managed early. Understanding when these pests are most active and how to respond can help safeguard your yields and reduce damage.
When to Watch for Black Cutworm
Black cutworm moths typically migrate north during the spring, laying eggs on low-growing weeds and crop residue. When temperatures begin to rise, larvae hatch and start feeding. This usually aligns with the early stages of corn emergence, making young plants especially vulnerable.
Peak risk periods often fall within the first few weeks of planting. Tracking degree-day accumulations, a measure of heat units that influence insect development, can help pinpoint when larvae are most likely to be active.
In general, action thresholds are met when larvae reach about 300 accumulated degree days after a major moth flight.
Spotting the Signs
Regular field monitoring is crucial to catch early signs of damage because black cutworm larvae feed at night and hide in the soil during the day. Watch for plants that appear wilted, cut off at the base, or missing entirely. Injury is usually most severe in fields with heavy residue or weed growth, which provide ideal egg-laying conditions.
Inspection should begin before the corn reaches the V5 growth stage and continue weekly during high-risk windows. Mark areas of concern and note any larvae found near the root zone or under debris.
Management and Prevention
If you find infestations and 2–5% or more of plants indicate damage, it's vital to act immediately. Timely application of insecticides can protect remaining plants if larvae are still small and feeding above ground.
Preventative strategies include weed control before planting and choosing insect-resistant hybrid varieties. However, even with resistant hybrids, early-season monitoring remains essential. Fields with a history of black cutworm issues or late tillage are especially at risk.
Begin scouting when corn emerges and continue through the V5 stage, when plants are most vulnerable to cutting. Monitor fields 7 to 14 days after significant moth flights, as larvae typically begin feeding during this window. In Iowa, for example, cutting often starts around mid-May, depending on planting dates and local weather. Use local extension updates to time scouting and treatments effectively.
Staying One Step Ahead
Early detection, timely intervention, and consistent monitoring are key to managing black cutworm. Being proactive can mean the difference between minimal damage and significant crop loss.
Want to stay ahead of black cutworms this season? Contact your local John Deere dealer for expert guidance and precision tools to protect your corn crop.