Cutworms remain one of the most persistent and damaging early-season threats to corn production across North America. These soil-dwelling larvae, primarily from the genus Agrotis, are nocturnal feeders that sever young seedlings at or below the soil surface, creating uneven stands and forcing costly replanting decisions. Understanding the biology, signs of damage, and targeted management strategies is essential for protecting yield potential from the very first emergence.
Identifying Cutworm Injury in Corn
Accurate identification begins in the field before any control measures are considered. Unlike some other pests, cutworm damage is often concentrated in distinct patches rather than scattered randomly across a field. Seedlings may be cleanly severed, partially clipped, or merely girdled, depending on the species and larval size. Examining the base of the plant and the surrounding soil for frass, or insect excrement, provides critical confirmation of the culprit.
Visual Signs and Symptoms
The most characteristic symptom of cutworm damage is a seedling that appears as if it has been sliced through with a knife, usually near the soil line. These severed plants are often found lying on the ground due to the larvae dragging them into their burrows for safe consumption. In some cases, particularly with climbing species, the damage appears as longitudinal scars or windowpane feeding on the leaves without severing the plant. Seedlings that are clipped below the growing point typically wilt and die, creating gaps in the row that are easily visible during scouting.
Common Cutworm Species Affecting Corn
Several species contribute to economic damage, each with slightly different habits and preferences. The black cutworm is the most notorious, migrating into fields in early spring and targeting the youngest, most vulnerable seedlings. Variegated cutworms climb the stalks to feed on the whorl and leaves, while dingy cutworms tend to remain near the soil surface. Knowing which species is prevalent in a specific region helps tailor monitoring and intervention timing.
Lifecycle and Timing of Activity Cutworms overwinter in the soil as pupae or partially grown larvae, with adult moths emerging in the spring to lay eggs on suitable host plants. The timing of hatch often coincides with corn germination, placing the larvae in direct contact with the emerging seedlings. Most feeding occurs during the cooler night temperatures of early growth stages, specifically between V1 and V6. As the corn plant grows rapidly and the soil surface dries, the larvae typically move out or are less able to reach the vulnerable base. Scouting and Monitoring Strategies
Cutworms overwinter in the soil as pupae or partially grown larvae, with adult moths emerging in the spring to lay eggs on suitable host plants. The timing of hatch often coincides with corn germination, placing the larvae in direct contact with the emerging seedlings. Most feeding occurs during the cooler night temperatures of early growth stages, specifically between V1 and V6. As the corn plant grows rapidly and the soil surface dries, the larvae typically move out or are less able to reach the vulnerable base.
Effective management starts with diligent scouting, especially in fields with a history of infestation or heavy residue. Walk the field in the late evening or early morning with a flashlight to catch larvae actively feeding. Focus on areas near field borders, weedy patches, and low-lying spots where moisture tends to persist. Look for severed plants, frass, and larvae hiding in soil cracks. Thresholds are generally triggered when 2% to 3% of plants are damaged, warranting intervention to protect stand establishment.
