Cutworms are the larval stage of several species of night-flying moths, common pests in gardens worldwide. These soft-bodied caterpillars earned their name from their habit of chewing through the stems of young plants at or just below the soil line, effectively “cutting” them down. This destructive feeding behavior can devastate entire rows of tender seedlings and transplants in a single night. Natural, non-chemical strategies focus on prevention, physical exclusion, and biological controls to manage these pests.
Identifying the Threat and Vulnerable Plants
Cutworm larvae are plump, smooth, and hairless caterpillars, typically one to two inches long. They are dull-colored, ranging from gray, brown, tan, or black, and curl into a tight C-shape when disturbed. These nocturnal feeders hide just under the soil surface or beneath plant debris during the day, making them difficult to spot.
The most severe damage occurs in early spring and early summer when overwintered larvae become active and target young, tender plants. Nearly all small seedlings and new transplants are susceptible. Plants like tomatoes, peppers, cabbage, lettuce, and corn are particularly vulnerable to being severed at the stem. A sudden loss of young plants, where the stem is cleanly clipped near the ground, is the primary sign of an infestation.
Physical Barriers and Hand Removal Methods
An immediate defense against surface-feeding cutworms involves creating simple physical barriers around young plants. Collars can be constructed from household items like cardboard toilet paper rolls, plastic cups with the bottoms removed, or strips of aluminum foil. These barriers should be placed around the stem, extending two to three inches above the soil line and pushed one to two inches into the soil to block burrowing access.
This barrier prevents the cutworm from fully encircling the stem, which is necessary for them to “cut” the plant. Another technique involves inserting a wooden stick, toothpick, or nail directly next to the plant stem. This creates a physical obstruction that prevents the caterpillar from coiling around and severing the stem.
To reduce the population, handpicking is a direct method, best done at night with a flashlight when cutworms are most active. During the day, search for them by gently scratching the soil surface, about one inch deep, near damaged or wilted plants. Any cutworms found should be removed and dropped into a container of soapy water.
Cultural Practices for Prevention
Long-term management involves adopting cultural practices that make the garden environment less appealing to the pests and their adult moths. Tilling the soil in late fall and again in early spring helps expose overwintering larvae and pupae to predatory birds and harsh weather. This disruption can significantly reduce the number of pests emerging at the start of the planting season.
Weed control is another practice, as adult moths are attracted to weeds and plant residue for egg-laying. Removing host plants like winter annual weeds and grasses one to two weeks before planting can starve young cutworm larvae before seedlings emerge. Cutworms prefer moist, undisturbed soil, so avoiding excessive watering and maintaining a strip of dry, bare soil around the garden perimeter deters their movement into planting beds.
Planting larger, more established transplants instead of tiny seedlings increases their survival rate. A thicker stem is more difficult for a cutworm to sever entirely, allowing the plant a better chance to recover from feeding damage.
Using Organic and Biological Treatments
Diatomaceous Earth (DE) is a natural, fine powder made from the fossilized remains of microscopic aquatic organisms. When applied around the base of vulnerable plants, the sharp edges of the powder abrade the cutworm’s waxy outer layer, causing dehydration and death. It should be sprinkled in a dry, one-inch-wide barrier on the soil surface in the evening when cutworms emerge. Reapply after rain or watering to maintain effectiveness.
Bacillus thuringiensis subspecies kurstaki (Btk) is a naturally occurring soil bacterium that acts as a stomach poison for caterpillars. Once ingested, the alkaline environment of the larval gut activates a crystalline protein toxin, paralyzing the digestive system and causing the pest to stop feeding. Btk is most effective against young, actively feeding larvae. Apply Btk to the base of the plants, particularly in the late afternoon or evening, as sunlight can degrade the bacteria.
Beneficial nematodes, specifically Steinernema carpocapsae, offer a subterranean control method by actively seeking out and parasitizing cutworm larvae in the soil. These microscopic roundworms enter the cutworm’s body and release symbiotic bacteria that kill the pest within 48 hours. Nematodes require moist soil for movement and survival. The application area must be watered thoroughly before and immediately after application, preferably in the early morning or evening to avoid UV light exposure.