How to control cutworm using organic and least-toxic methods.
Many species of cutworms are found in home gardens across the United States. Damage occurs at night when caterpillars feed by clipping off seedling stems and young plants near or just below the soil surface. Often, an entire row of newly planted garden vegetables will be cut off during the night. As general feeders, cutworms attack a wide variety of plants. Common hosts include beets, cabbage, broccoli, kale and cauliflower. A few species will also climb foliage and chew holes or bore into heads of lettuce or cole crops.
Cutworm larvae are stout, soft-bodied, gray or dull brown caterpillars (1-2 inch long) that curl up when at rest or disturbed. They feed at night and burrow into the soil during the day. Adults are dark gray or brown, night-flying moths (1-1/2 inch wingspan) with ragged blotches or stripes on their wings. They do not damage plants.
Note: Pest populations vary greatly from year to year and when numerous may destroy up to 75% of a crop.
Most species pass the winter in soil or under garden trash as young larvae. In the spring, as temperatures warm, they become active and begin feeding on plants at night, remaining hidden during the day. The larvae molt several times and when fully grown pupate in the soil (late spring). Within one week moths emerge and begin laying hundreds of eggs mostly on stems and leaves. One to five generations per year, depending upon the species.
Note: Overwintering larvae and the first generation in the spring are the most damaging. A few species pass the winter as pupae or hibernating moths.
Before planting a new garden remove weeds and plant debris to starve developing larvae. Handpick caterpillars after dark. This is often most productive following a rain or thorough watering. Place cardboard collars (or toilet paper tubes) around transplant stems at planting time. Beneficial nematodes will attack and destroy cutworms in the soil. Release trichogramma wasps weekly for three consecutive weeks to parasitize cutworm eggs. Diatomaceous earth sprinkled around the base of plants is very effective. Scatter bran or corn meal mixed with Monterey Bt (Bt-kurstaki) and molasses on the soil surface to kill caterpillars. Eco-Bran will also kill caterpillars that feed on it. After harvest pick up garden debris and turn the soil over around plants to disturb overwintering larvae.
Note: Gardens that were covered in grass or weeds the previous season are especially attractive to this pest.