Cutworms are moth larvae that hide in the soil during the day, and then come out at night to feed on plants. They get their name from their ability to "cut off" a seedling at ground level by chewing through the stem at or just below the soil level. The larvae of many species of adult moths are called cutworms, although they are actually caterpillars, not worms. They do not bite or sting; if disturbed, they will roll up into a c-shape. While they are not harmful to humans, they can be a major problem in the garden.
Cutworms are voracious leaf, bud, and stem feeders and can destroy plants. Some species are subterranean and eat roots as well.Cutworms do their damage only when they are in the larval stage. Adult cutworm moths do not damage plants. Early in the growing season cutworms chew off seedling, young transplants, garden vegetables, and flowers. Later in the season these pests can also injure the crop by eating irregular holes in the surface of young fruits or vegetables, and causing fruiting stems to wilt and fail. On grapevines, cutworms feed from the bud swell stage until shoots are several inches long. Injured buds may fail to develop. A few cutworm species also climb up on foliage and chew holes or bore into heads of lettuce or cole crops like kale and cabbage.
Citrus cutworm moth and eggs, Jack Kelly Clark, UC ANR
Cutworms are grouped into 3 general categories:
1) Surface cutworms: do considerable damage to leaves and stems.
2) Climbing cutworms: climb onto plants and eat buds, leaves, and fruit.
3) Subterranean cutworms: stay on or below ground and feed on the roots of plants.
Identifying Cutworms. Cutworms belong to the insect order Lepidoptera (butterflies and moths). A cutworm moth will typically lay 350-800 pearl-shaped eggs. Mature cutworm larvae (caterpillars) are one to two inches long, plump, soft bodied, and often have longitudinal stripes. Depending on their species, they can be gray, green, black or dull brown in color, and solid, spotted, or striped. At the end of its larval stage, a cutworm will rest in the soil for about a week before pupating below the soil layer. Cutworm pupa are reddish-brown in appearance and can be found at or below soil level. It is during the pupal stage that the adult winged form develops. Adult cutworm moths are dark gray, black, or brown in color, with markings on their front wings. Cutworm species can only be reliably identified in the moth phase through wing color and pattern. Females are darker than males.
Larva of citrus cutworm. Jack Kelly Clark, UC ANR
The Cutworm Lifecycle. Depending on the species, there can be one or more generations of cutworms per year. Most species pass the winter in the soil or under garden waste as young larvae or pupae. Adult moths emerge from the pupal stage in spring, mate, and females lay eggs 5 to11 days after emerging. Cutworm eggs hatch in April or early May, and the young cutworm caterpillars feed on vegetation near the ground. After 14 days, they avoid daylight and become nocturnal, coming out at night to feed heavily on seedlings and young plants. The young larvae of most species pass through 6 stages (instars), each separated by a shedding of skin (molting). Larvae fully develop in 24 to 40 days and then pupate. The pupal stage generally lasts 21 to 34 days, but can take longer, depending on the temperature. Adult cutworm moths are also nocturnal. They measure about one and one-half inches long with a one-and-one-half-inch wingspan.
Cutworm pupae, Michelle Ramsey
Management and Control. Plant collars can be used to protect tender transplants, because cutworms need to completely encircle a stem in order to munch it off. Make a collar out of cardboard, plastic, or aluminum foil. Paper cups (with bottoms removed) or tin cans (with both ends removed), also make good collars to place over young plants. Place a collar around each stem extending it one to two inches into the soil and two to three inches above the soil.
Cutworm, Jack Kelly Clark, UC ANR
- Control weeds, grasses and plant debris both in and around the garden to reduce habitat and food favored by young cutworms.
- Keep up with cultivation. Moths prefer to lay eggs in high grass and weeds. At the end of the season, till your garden and mow surrounding areas to destroy their over-wintering habitat.
- A few weeks before planting your garden, dig the soil down about two inches, and squash any caterpillar larvae and/or pupae you find manually (or drop them into a bucket of soapy water).
- Once larvae emerge from pupae, hand-picking at night with a flashlight is very effective. Clip and dispose of infested foliage and blossoms.
- Pesticides are not very effective and can harm beneficial insects, so they are not recommended.
Natural Enemies.Cutworms are attacked by a large range of natural enemies. The most important are parasitic wasps and flies, and some predators. The most common predators include ground beetles, lacewings, praying mantis, ants, and birds. Hens are useful because they dig out and eat cutworms present near the soil surface. Hens are very effective when confined on garden beds prior to planting.
Larva of citrus cutworm, Jack Kelly Clark. UC ANR
Additional information on cutworm damage on fruits and vegetables can be found here on the UC IPM website.
The UC Master Gardeners of Butte County are part of the University of California Cooperative Extension (UCCE) system. To learn more about us and our upcoming events, and for help with gardening in our area, visit our website. If you have a gardening question or problem, call the Hotline at (530) 538-7201 or email firstname.lastname@example.org.