Cutworms are moth larvae that hide in growing media or debris by day and feed at night, often chewing through young seedling stems at or just below the media.
Identification
Larva body: Larvae are usually smooth, soft, and thick-bodied, often gray, brown, tan, greenish, or nearly black depending on species and age.
Curling behavior: Cutworms commonly curl tightly into a C-shape when handled or exposed, which helps distinguish them from many other larvae.
Feeding location: Damage is usually concentrated at the media line, crown, lower stems, or nearby leaves.
Seedling damage: Young plants may be severed cleanly or partly chewed through near the media surface, causing sudden collapse.
Feeding time: Larvae usually feed at night and hide during the day under media particles, trays, leaves, or debris.
Frass: Small dark droppings may be found near damaged seedlings, leaf edges, or media hiding sites.
Lookalikes
Fungus gnats: Fungus gnat larvae are small, translucent, legless larvae with dark heads that damage roots rather than cutting stems.
Armyworms: Related caterpillars that often feed more openly on leaves and can move in groups; some species overlap with cutworm behavior.
Slugs: Slugs also feed at night and damage seedlings, but leave slime trails and rasped leaf damage rather than caterpillar frass.
Wireworms: Wireworms are hard, yellow-brown beetle larvae that bore into roots and tubers rather than soft-bodied caterpillars that cut stems.
Environmental Triggers
Debris on media surface: Plant debris, algae mats, old leaves, and tray clutter provide hiding sites for larvae during the day.
Mild night temperature: Cutworms feed actively during mild nights when seedlings are tender and conditions are sheltered.
Moderately moist media: Moist media helps larvae hide and pupate, though overly saturated systems may reduce survival for some species.
Open greenhouse or outdoor access: Open doors, vents, and outdoor-adjacent production increase the chance that adult moths lay eggs near crops.
High sanitation: Removing debris, weeds, and crop residues reduces egg-laying sites and larval shelter.
Moth exclusion screening: Screens and sealed openings reduce adult moth entry and egg laying in protected culture.
Media surface disturbance: Careful inspection and disturbance around damaged seedlings can expose hiding larvae for removal.
Treatment
Sanitation and debris removal: Remove dead leaves, old crop residues, algae mats, weeds, and unused media from benches and floors. Keep seedling trays clean and elevated where possible. Inspect incoming transplants and media before placing them near production crops. Dispose of damaged plants and hidden larvae away from the grow area.
Night inspection and hand removal: Inspect damaged trays or beds after dark with a flashlight. Search around the cut stem, just under the media surface, and beneath nearby debris. Remove curled larvae by hand or with tweezers. Repeat nightly for several days after new damage appears.
Seedling collars: Place small collars around vulnerable transplants using clean paper, cardboard, plastic, or similar safe material. Set the collar slightly into the media and extend it above the stem base. Use collars during the vulnerable seedling stage, then remove or adjust as stems thicken. Check collars for trapped moisture or hidden pests.
Bacillus thuringiensis kurstaki: Use a Bt kurstaki product labeled for edible crops and caterpillar pests. Apply to foliage and stem bases where larvae are feeding. Target young larvae because larger larvae are harder to control. Repeat according to label directions after irrigation, rinsing, or new growth.
Beneficial nematodes: Use nematode species labeled for caterpillar or soil-dwelling larvae where available. Apply to moist media in the evening or low-light conditions. Keep media moist after application so nematodes remain active. Avoid applying with incompatible disinfectants or pesticides.
Adult moth monitoring traps: Place traps near entry points or outside the main crop canopy according to product guidance. Check traps regularly for noctuid moth activity. Use trap captures as a trigger for seedling inspections and exclusion checks. Avoid placing bright traps where they may draw moths into the production area.
Screening and entry management: Install or maintain insect screens on vents, doors, and intake points. Keep doors closed during evening moth activity when practical. Inspect outdoor-grown starts before bringing them indoors. Remove weeds near greenhouse or grow-room entrances.
Labeled caterpillar insecticide: Use only products labeled for edible crops, caterpillars or cutworms, and the specific production environment. Follow all label rates, worker safety directions, and harvest intervals. Avoid unapproved soil drenches or products incompatible with recirculating hydroponic systems. Combine with sanitation and physical removal because larvae hide in media and debris.
Trap or companion planting: Use companion or trap crops only as a supplementary strategy. Inspect trap plants frequently and remove larvae before they spread. Do not allow trap plants to become a hidden pest reservoir. Combine with screening, sanitation, and night inspection.
Lifecycle
Egg laying: Adult moths lay eggs on leaves, stems, weeds, tray edges, media surfaces, or nearby structures.
Egg hatch: Eggs hatch into small larvae that begin feeding on tender foliage, stems, or nearby plant material.
Larval feeding: Larvae grow through several instars and cause the most damage, especially by cutting seedlings or chewing stems at night.
Pupation: Mature larvae pupate in media, substrate, debris, or sheltered cracks near the crop.
Adult moth emergence: Adult moths emerge, mate, and can start another generation if host plants and sheltered conditions are available.