Cutworms are moth larvae that attack tomato plants, most notoriously by severing young seedlings right at the soil line overnight. You can walk out to your garden in the morning and find a healthy transplant toppled over as if someone snipped it with scissors. Several species cause this damage, and the good news is that simple physical barriers and cultural practices can stop them effectively.
What Cutworms Are
Cutworms are the larval stage of various night-flying moth species. The most common types found on tomatoes include the black cutworm, variegated cutworm, spotted cutworm, and yellow-striped cutworm. They’re smooth, hairless caterpillars that grow to 1.5 to 2 inches long when fully mature. Colors range from gray, brown, and black to green, and the body may be solid, spotted, or striped depending on the species.
The black cutworm is gray to black with a greasy sheen. Variegated cutworms are brown to gray with white or yellow spots along the back and a dark “W” marking on the rear abdominal segments in their final larval stage. If you find one and poke it, the caterpillar will curl into a tight C shape as a defensive reflex. That curling behavior is one of the easiest ways to confirm you’re dealing with a cutworm rather than another garden caterpillar.
How They Damage Tomato Plants
Cutworms feed almost exclusively at night. During the day, they hide in the soil, under dirt clods, or in debris at the base of plants, which is why you rarely catch them in the act. The damage they cause changes as the season progresses.
Early in the season, cutworms cut down seedlings and recently transplanted tomatoes at the soil line. A single larva can destroy multiple plants in a row over consecutive nights. This is the most devastating type of damage because it kills the plant outright. Later in the season, once plants are too thick-stemmed to sever, cutworms shift to feeding on fruit. They chew irregular holes into the surface of tomatoes, and fruit resting on the ground is the most seriously injured.
Life Cycle and Timing
The entire cutworm life cycle, from egg to adult moth, takes 35 to 60 days depending on temperature and food availability. In northern climates, black cutworms can’t survive freezing winters in the soil. Instead, adult moths migrate south to overwinter in Texas and Mexico, then return north on spring storm fronts. This means cutworm pressure in a given year depends partly on weather patterns that carry migrating moths into your region.
Depending on when moths arrive in spring and how warm the summer gets, cutworms may complete one or more generations per season. Moths lay eggs on weeds and plant debris, so gardens with lots of early-season weed growth tend to attract more egg-laying activity.
Cutworm Collars: The Best Physical Defense
The single most effective protection for tomato transplants is a simple collar around each stem. The concept is straightforward: a short tube of rigid material encircles the seedling, creating a barrier the cutworm can’t chew through or crawl over to reach the stem.
Toilet paper tubes are the classic DIY option. Cut one in half to get two collars roughly 2 inches tall, then slip the tube over the transplant and push it about 1 inch into the soil, leaving 1 inch above the surface. The buried portion stops cutworms from tunneling underneath. You can also cut collars from paper towel rolls, cereal boxes, or card stock to the same dimensions.
For longer-lasting barriers, cut sections of PVC pipe 3 to 4 inches tall and push them 1 to 2 inches into the soil. Plastic cups with the bottoms removed, rings cut from mayo jars or plastic bottles, and even small metal cans with both ends removed all work. Aluminum foil wrapped around the base of the stem, extending below the soil line and about an inch above, is a quick alternative that conforms to any stem size. The key principle is the same regardless of material: the barrier must extend below the soil surface and stand at least an inch or two above it.
Cultural Practices That Reduce Cutworm Pressure
Cutworm infestations develop on early-season weed growth. Moths prefer to lay eggs on weedy ground with plenty of organic debris, so keeping your garden beds clean is genuinely preventive. Remove weeds and plant debris in fall to discourage egg-laying by migrating moths heading south. In spring, cultivate the soil at least two weeks before transplanting tomatoes. That two-week window matters: if you till and plant immediately, any cutworms already present in the soil will have nothing to eat except your new seedlings. Giving them two weeks without food after cultivation lets the population starve down or move on before your plants go in.
No-till and reduced-tillage beds, while great for soil health, do carry higher cutworm risk. The extra crop residue and weed cover create exactly the habitat cutworms prefer. If you garden with minimal tillage, physical collars become even more important as your primary line of defense.
Biological and Organic Treatments
When collars and cultural controls aren’t enough, a soil-dwelling bacterium called Bt (Bacillus thuringiensis) is the go-to organic treatment. Bt produces proteins that are toxic to caterpillars but harmless to humans, pets, and beneficial insects like bees. Two subspecies are effective against cutworms: Bt kurstaki and Bt aizawai. These are sold under brand names like DiPel and XenTari and come as dusts or liquid concentrates you apply to the soil surface and base of plants where cutworms feed.
Bt works best on younger, smaller larvae. Larger cutworms in their final growth stages are harder to kill with any biological product, so early application matters. Because cutworms feed at night and hide in soil during the day, evening applications tend to be more effective.
Other organic options include neem-based products, which act as insect growth regulators that disrupt molting, and pyrethrin sprays derived from chrysanthemum flowers. Diatomaceous earth, a powder made from fossilized algae, can be spread around the base of plants to damage the cutworms’ soft bodies as they crawl through it. These approaches work best as part of a combined strategy rather than standalone solutions.
Finding Cutworms in Your Garden
If you suspect cutworm damage, the best time to confirm it is after dark with a flashlight. Check the soil surface around damaged plants and you’ll often find the larvae actively feeding. During the day, dig gently in the top inch or two of soil within a few inches of the damaged stem. Cutworms typically hide right at the base of the plant they’ve been feeding on. You can also look under soil clods, mulch, and garden debris nearby.
Hand-picking at night is surprisingly effective in small gardens. A few minutes with a flashlight on consecutive evenings can remove enough larvae to stop the damage, especially if you combine it with collars on your remaining healthy transplants. Birds, ground beetles, parasitic wasps, and firefly larvae all prey on cutworms naturally, so maintaining habitat for beneficial insects and avoiding broad-spectrum pesticides helps keep populations in check over time.