June 3, 2010 at 8:38 a.m.
Cutworms are the larvae of several species of night-flying moths. The larvae are called cutworms because they cut down young plants as they feed on stems at or below the soil surface. The adult moths do not cause any damage but the cutworms feed on a wide range of plants. Some common vegetable hosts include asparagus, beans, cabbage family plants, carrots, celery, corn, lettuce, peas, peppers, potatoes, and tomatoes. In other words, they eat just about every vegetable we plant.
The most common species of cutworms in Minnesota gardens are the bronzed, variegated, black, dingy, glassy, and army cutworms. Cutworms can be quite distinct from one another, and their coloring can vary from brown or tan to pink, green or gray and black. Some cutworms are a uniform color while others are spotted or striped. Cutworms crawl up into a tight "C" when disturbed.
Some cutworms migrate into the state from the south each year. However, other species, including dingy, bronzed, and glassy cutworms are native to Minnesota and overwinter as eggs or larvae. Female moths can lay hundreds of eggs, singly or in small clusters. Newly emerged weeds can be very attractive sites for egg laying and feeding by the small larvae. At this stage they begin feeding on seedling stems, either cutting through them or burrowing into them. I have never seen them this large, but it is said that some larvae may grow to two inches long. They may go through as many as three generations per year. Cutworm abundance and development is greatly affected by weather, especially rainfall.
Most cutworm damage occurs on vegetable seedlings early in the season when plants are small and have tender tissue. Although cutworms are active throughout the summer, they are usually not a problem after spring. The variegated cutworm can climb the stem of trees, shrubs, vines, and garden plants and eat the leaves, buds and fruit. Other species, such as glassy cutworms remain in the soil and feed upon roots and underground parts of the plant.
Regularly check your garden, especially during late afternoon and evening when cutworms are more active. Watch for plants cut off near the ground or plants that are wilting. To verify cutworms are present, dig around the injured plant within a square foot of the plant.
You can control them by placing aluminum foil or cardboard collars around the transplant. Be sure the collars are around the plants, making sure one end is pushed a few inches into the soil, and the other end is extending several inches above the ground. Some gardeners put a stick next to the stem to deter the cutworms. The use of insecticide is usually not necessary, but you can protect plants with a residual product if you are experiencing a severe problem. For best results, apply insecticides in the evening. Examples are carbaryl, cyfluthrin, or permethrin. Be sure to read labels carefully before buying and applying.
Parts of this article are taken from information gathered by Jeffrey Hahn and Suzanne Wold-Burkness at the U of M. Extension Service.