Cutworms

Garden pest

Description

Cutworms are caterpillars of several noctuid moth species, not a single species. They are named for their habit of cutting through young plant stems at or near the soil surface. Most feed at night and hide during the day in soil, mulch, or debris close to their host plants. Depending on the species, they may also chew leaves or feed below ground on roots. Seedlings and newly set transplants are most vulnerable: a plant can look healthy one evening and be toppled by morning. Cutworms attack many vegetables and flowers, including tomatoes, peppers, beans, and cabbage-family crops. Adult moths lay eggs on plants or nearby vegetation; the caterpillars that hatch do the damage. An individual caterpillar may injure several seedlings as it moves through a bed. Damage is often greatest early in the growing season, when small plants have stems that are easy to sever.

Symptoms

• Stems chewed or cut through
• Seedlings collapse at soil level
• Wilting
• Holes in leaves

How to Identify

Look for seedlings severed cleanly or raggedly at the soil line, sometimes with the fallen tops lying nearby. Check after dark with a flashlight, or gently scrape the top few centimeters of soil around a newly damaged plant. Cutworms are usually smooth, plump caterpillars, often gray, brown, or mottled, that curl into a C when disturbed. Species vary in color and markings. Slugs leave slime trails and usually chew irregular holes rather than cutting stems. Damping-off disease can also topple seedlings, but their stems typically look pinched, soft, or rotted at the base rather than chewed. Birds or other animals may pull seedlings out entirely.

Prevention

Clear weeds from a planting bed several weeks before sowing or transplanting to reduce places where moths can lay eggs and caterpillars can feed. Before planting, inspect the soil and remove any cutworms you find. Protect vulnerable transplants with a loose cardboard or plastic collar around each stem, extending about 2–3 cm below the soil and several centimeters above it; check that no leaves or weeds bridge the collar. Remove collars once stems are sturdy. Check newly planted beds regularly, especially in spring and after a previous cutworm problem. Starting with larger, healthy transplants can help plants withstand minor feeding. Keep mulch slightly back from seedling stems so the soil surface is easier to inspect, while avoiding unnecessary disturbance of beneficial insects elsewhere in the garden.

Treatment

First, inspect damaged plants at dusk or after dark. Gently search the soil immediately around them and hand-pick any cutworms; repeat for several evenings. Put collars around surviving seedlings and replacements to prevent further stem cutting. If the infestation continues, beneficial nematodes sold for soil-dwelling caterpillars may help when applied to moist soil at the temperature specified on the package. Products containing Bacillus thuringiensis subsp. kurstaki (Bt) can work on small caterpillars that eat treated foliage, but are less useful for cutworms feeding at the soil line or underground. If damage remains severe, use only a pesticide labeled for cutworms and for the crop or site, applying it precisely as directed. Avoid broad, routine spraying: it can harm beneficial organisms without reaching caterpillars hidden in the soil. Replace badly damaged seedlings once you have protected the planting area.

Plants Affected

Barley, Celery, Chickpea, Corn, Edamame, Endive, Green Bean, Lettuce, Quinoa, Radicchio, Sweet Potato

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