Cutworms

5/19/22
This resource is offered as part of MOFGA’s Pest Reports Fact Sheet Series

Pest: Cutworms (many species)

Pest/disease identification and lifecycle, most common damage symptoms and crops affected:

Cutworms

Cutworms are occasional pests of many crops early in the season, including carrots, peas, onions, spinach, broccoli and the list goes on and on. Some years they result in major losses, other years result in no loss at all. They are larvae of a dozen or so different species of night flying moths. They are greasy looking caterpillars that have a habit of curling into a “C” shape when disturbed. Many species overwinter as partially grown larvae, and can become active very early in the spring when the plants first germinate or are transplanted and are very susceptible. Others arise from eggs laid by moths that fly early in the spring, and these feed well into the early summer. Cutworms hide in the soil during the day and crawl on the surface at night. They feed and cut off young seedlings at the soil surface, or climb up and chew on the leaves. During the day, you can dig around an inch or two deep around damaged plants and often find the ugly critter. Chickens love them.

Management options:

Cultural:


Since most species lay their eggs in the late summer/fall on vegetation, keeping fields clean of weeds and crops in the fall helps. Of course, this goes counter to the recommendations to keep the soil cover cropped, so it is a management decision based on how bad the problem has been. Fall plowing exposes larvae to birds. Cultivating fields in the spring just after vegetation has appeared and grown a few inches, and keeping it clean cultivated can starve the cutworms out before plants go in. But in most areas in Maine this is not practical because crops need to be planted when possible.
On a small scale, collars inserted into the soil around each plant will keep the caterpillars away — gardeners have come up with many different designs, though plastic cups with their bottoms cut off and a slit up the side to facilitate easier removal seem most promising to me. Going out at night with a flashlight and hand picking breakfast for your chickens can also work, and may promise more catharsis.

Biocontrol options:

Entomopathogenic nematodes show good efficacy when environmental conditions are favorable. Steinernema carpocapsae has been shown to be very effective against cutworms. Success with nematodes depends on proper application methods. Be sure to follow the instructions from the supplier carefully. A few suppliers of these insect-attacking nematodes are IPM Laboratories (ipmlabs.com), and ARBICO (arbico.com).

Organic pesticides (as a last resort):

Baits — Spinosad or Bt will kill the caterpillars, but getting the pest to consume the insecticide as a sprayed on material before significant damage is done is not likely. However, farmers and gardeners have reported good results using these materials in baits. The bait is spread on the ground near the plants, or prior to planting to clean out an area.

Spinosad — Seduce is an OMRI-listed commercial bait.

Bt — A bait made from Bt is often recommended and has received good reports from farmers. This is a method of use for Bt that is not described on the label. This off-label use is permitted by EPA under FIFRA 2ee, but growers should check with their state pesticide regulators about their state regulations. Make the bait by mixing the highest concentration solution of Bt allowed on the label and then mixing in a bit of molasses and alfalfa meal or bran. Then dampen this mix if necessary. Spread the bait along the planted or planned rows in the evening.

Source material attribution: Written by Eric Sideman, MOFGA crop specialist emeritus.

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