Cutworms in the Home Garden

Introduction

Cutworms are caterpillars that feed at night on plants in vegetable gardens, field crops, and lawns. The name “cutworm” refers to their habit of severing plant stems as they feed. This damage is most commonly seen in the spring on young plants or new transplants with small stems and tender growth. Many species of cutworms damage agricultural plants throughout Virginia and they are particularly destructive to early season plantings.

Damage

Cutworm damage is more commonly seen than the caterpillars themselves. Cutworms feed during the evening or at night and hide in shallow burrows in the soil or under plant debris during the day. The caterpillars can be found during the day by brushing away debris under or near damaged plants or carefully digging them out of their shallow burrows.
Cutworms often sever plants at the base near the soil line (Fig. 1), but some species climb to feed on the leaves, buds, or fruits of plants. Other cutworms feed on the underground portions of a plant.

Description

Cutworms are dull gray, brown, or black caterpillars (Fig. 2). Some species have stripes or spots on their back or sides (Figs. 3 & 4). The bodies are stout, smooth, with few hairs. They typically measure up to 1.25 inches long when mature. Some may have a “greasy” appearance while others are dull. Cutworms characteristically curl up into a tight C-shape when disturbed (Fig. 1).

Common Hosts

Cutworms attack a wide range of vegetables often planted in home gardens. Common hosts include beans and peas; beets; cabbage; carrots and parsnips; cauliflower; celery; collards and kale; cucumbers; endive and lettuces; melons; onions; tomatoes, peppers, and potatoes; parsley; radishes; and sweet corn.

Distribution

Cutworms are widespread throughout North America. They are more commonly found on low-lying ground near streams and rivers. They prefer areas with abundant weedy growth that can serve as host plants or places to hide.

Cultural Control

Place a stiff cardboard collar around the stems of vulnerable host plants to protect them against cutworm feeding. It should extend 1 inch above the soil and 2 inches below ground, with a half inch clearance around the stem. An empty paper towel roll is ideal for this use. Also, till the garden to kill any overwintering larvae and overwintering weeds. Remove any nearby weedy growth in the spring to eliminate food sources and hiding places for cutworms. Handpicking cutworms seen at night with a flashlight will provide some control if their numbers are low and caterpillars are removed while they’re still young.

Organic/Biological Control

The Bacillus thuringiensis strain for caterpillars (Bt var. kurstaki), sold under various trade names and formulations, is effective against young cutworms. Some formulations of Bt are sold as “cutworm bait.” When the caterpillars ingest the Bt, they stop feeding but may take a few days to die. Since Bt kurstaki is specific to caterpillars, it’s considered more environmentally friendly than an insecticide treatment.

Chemical Control

If cultural control methods are ineffective, consider using an insecticide-based cutworm bait or a granular insecticide specifically labeled for vegetable gardens. Follow all precautions on the label. Treat as soon as cutworm damage is found. In areas with heavy cutworm losses the previous year, consider using a pre-planting treatment. For chemical recommendations, see the current VCE Pest Management Guide for Home Grounds and Animals.

Important species of cutworms

The black cutworm (Fig. 2) and the bronzed cutworm (Fig. 3) are the two most common cutworm pests in Virginia. Both will attack newly emerged plants and young transplants in the spring. Like other cutworms, they are active all summer but rarely cause significant damage after the spring.
The variegated cutworm (Fig. 4) is known as a climbing cutworm. The larvae climb garden plants, trees, shrubs, and vines to feed on plant parts above the ground.

Interesting Facts

The adult stage of cutworms are medium-sized moths that are often seen at porch lights. They range in color from light tan to dark brown (Figs. 5), often with contrasting patterns on the first pair of wings. The adults do not feed on plants and cause no damage.