Identification

Cutworms are dull-colored caterpillars ranging in length from 1 to 2 inches when fully grown. The color and markings of their bodies blend well with the soil, where they are frequently found, especially during the day.

Life Cycle

Cutworms that attack grapes overwinter in vineyard soil, trash, or grass clumps as immature larvae. Some move under the vine bark. When temperatures become warm in early spring, the larvae become active, emerging at night to feed on many kinds of plants. Feeding continues for about 10 days to 2 weeks during rapid bud and shoot growth. Larvae then return to the soil and hollow out cells or chambers to pupate. The pupal stage lasts 7 days or more and moths emerge from April through mid-May.

Eggs are laid singly or in groups on leaves, twigs, or stems. The egg stage lasts from 2 days to 2 weeks, and hatching larvae feed on low-growing vegetation. Moths resulting from this brood lay eggs to produce the late-summer larvae that overwinter.

Most cutworm species have one or two generations per year, but some have three or four generations and moths may be found from spring to fall.

Damage

Damage to grapevines occurs from bud swell to when shoots are several inches long. Buds are eaten out and new shoots are eaten partway through. Injured buds may fail to develop canes or clusters, which can cause yield reduction.

Solutions

Cutworms are pests only in the spring. Vines usually outgrow this damage. Pesticides are not very effective and not recommended for backyard grapes. Working grasses and weeds into the soil in fall or early winter destroys many eggs and young larvae. Do not destroy weeds at budbreak because this will drive cutworms onto vines.