Cutworm - Vegetables

Plants cut off at the soil line is symptom of cutworms

Appearance

• Eggs: Tiny, white-brown spheres (black cutworm) or half-spheres (variegated cutworm), with ribs radiating from center, laid on foliage in clusters of up to several hundred.  
• Larvae: Stout caterpillars with rough skin, almost 2” long when full grown (there are usually 6 instars). Black cutworm: uniformly gray/brown to nearly black, somewhat greasy sheen. Variegated cutworm: brownish/gray to grayish/black with yellow-white spots on its back and a dark “W” mark on its 8th abdominal segment of last instar (growth stage).
• Pupae:  Dark brown/mahogany colored case, ¾ - 1” long, in a chamber near soil surface.
• Adults: Moths with up to 2" wingspan. Black cutworm: wings uniformly dark brown with black “dash” marking on forewing. Variegated cutworm:  wings grayish/brown with darker bean-shaped spot and smaller round spot usually visible on each wing.

Life cycle/habits

• Cutworms are important early-season pests of vegetable crops in Maryland.
• They typically overwinter as pupae, with additional adult moths migrating in from the south in spring.
• Adult moths feed on nectar from flowers and lay eggs on foliage.
• Early instar (life stage) larvae may feed during the day, but larger larvae feed at night and seek shelter during the day in soil or elsewhere.
• Young larvae begin feeding on foliage in early May.
• Older larvae feed near the soil surface, cutting off young plants at or below ground surface and sometimes pulling them underground to consume.
• Larvae are also defoliators and may feed on fruits, roots, and tubers as well.
• Variegated cutworms readily climb trees to feed on buds, foliage and even tree fruit.
• Cutworms curl up when disturbed.
• There are several generations a year.

Host plants

• Extremely wide host plant range. Primarily tomato and corn, but also feed on asparagus, beans, beet, brassicas, broccoli, cantaloupe, carrot, celery, collards, cucumber, eggplant, lettuce, okra, onion, peas, pepper, potato, radish, rhubarb, spinach, squash, sweet potato, turnip and watermelon, plus tree fruits, and small fruits.

Signs/symptoms

• Seedlings or even transplants are cut off at the soil line or disappear entirely at night (dragged underground into cutworm burrows). 
• Feeding damage appears on foliage, fruit, or buds, often without any pest visible during the day.
• Variegated cutworms may tunnel into tomatoes or cabbage and cauliflower heads. 
• Cutworms may feed on storage roots or tubers, making smooth cavities.

Monitoring

• Watch for seedlings cut off at the soil line or disappearing altogether at night. The first generation of mature cutworm larvae does the most damage.

Prevention/control

• Most feeding injury is superficial and can be ignored.
• In spring or fall, till soil to disrupt possible overwintering sites, exposing pests to predators and freezing temperatures.
• Larger transplants better withstand damage. Pre-sprouting seeds is also helpful.
• Floating row cover prevents egg-laying and excludes larvae.
• Protect seedlings with a 3" cardboard, foil or plastic collar pushed into soil around plant stems.
• Discourage cutworms with coarse materials such as crushed oyster shell, sand, or diatomaceous earth, placed around plant stems.
• Handpick larvae, and either crush them or drop them into a container of soapy water.
• Bacillus thuringiensis (Bt), an organic pesticide, will kill young larvae.