A seedling gets found flat on the ground one morning. Cutworms get the blame almost automatically.
Sometimes that blame is wrong. Rabbits, slugs, and even a few soil dwelling insects leave damage that looks similar at first glance.
This guide covers how to actually confirm cutworm damage rather than assume it. It also covers the one cutworm species that breaks the usual rules, and what extension sources say actually helps.
The short version
Cutworms on tomatoes are smooth, hairless caterpillars. They cut young seedlings off right at the soil line.
Most species feed at night. They hide in soil during the day and curl into a tight C shape when disturbed.
Not every flattened seedling is cutworm damage, though. Rabbits cut stems at a 45 degree angle well above the soil, while cutworms leave a flush cut right at ground level.
Variegated cutworms break the usual rules entirely. Unlike most cutworm species, they climb the plant and feed on upper leaves and fruit instead.
Cardboard or foil collars pushed into the soil are the most reliable defense. Tilling the soil ahead of planting and hand picking visible cutworms at night both help too.
What a cutworm actually is
Cutworms are the larval stage of several different moth species. University of Connecticut Extension identifies black, yellow striped, and variegated cutworms as the main species affecting tomatoes.
Black cutworms have a gray to almost black color. Their skin has a slightly greasy looking sheen.
Variegated cutworms run brown to gray, with pale spots. A dark W shaped marking sets them apart from the other species.
All three species share a similar basic body plan. They grow smooth and hairless, typically 1.5 to 2 inches long once mature.
Color varies between gray, brown, black, or green. When disturbed, a cutworm curls into a tight C shape.
That defensive posture is one of the most reliable ways to confirm a caterpillar really is a cutworm. Most damage happens at night.
Cutworms hide just below the soil surface during the day. They emerge after dark to feed on stems at ground level.
Why cutworms get blamed for damage they didn’t cause
Cutworm damage has a specific signature. The top of a young plant separates cleanly, right near where the stem meets the root.
The caterpillar sometimes drags the severed top into its burrow. Other culprits leave a different pattern entirely.
Rabbits cut stems at a 45 degree angle. That cut often sits well above soil level, rather than flush with the ground, according to Purdue University’s Vegetable Crops Hotline.
Rabbit damage also tends to march down a row in a consistent pattern. That is a different signature than the more scattered losses cutworms typically cause.
A Garden.org forum thread shows how easily this gets misdiagnosed. A gardener named MarcSloane reported total losses across an entire planting.
He tried BT, diatomaceous earth, beneficial nematodes, and insecticide granules. None of it worked.
Fellow forum member deepsouth pointed something out. The damage pattern, leaf consumption rather than clean stem cuts, did not actually match cutworm behavior.
MarcSloane set out beer traps and caught eight slugs. Slugs turned out to be the real cause all along.
The cutworm that breaks its own rules
Most cutworm species stick to seedlings and stay near the soil line. Variegated cutworm does not follow that pattern.
University of Connecticut Extension notes that variegated cutworms climb up the plant instead. They feed on upper leaves and fruit, causing irregular surface damage rather than a clean cut at the base.
That climbing habit changes the risk window. Variegated cutworm can damage mature, established plants, not just young transplants.
A gardener who assumes cutworm risk ends once seedlings toughen up can still lose fruit to this species later in the season.
What actually helps
Physical collars are the most consistent defense against the classic soil line cutting behavior. A ring of cardboard, aluminum foil, or a cut down cup works well.
Push it a couple inches into the soil around each transplant. That physically blocks a cutworm from reaching the stem.
Real gardeners back this up with their own methods. On a Houzz gardening forum, a poster named Stone described using aluminum foil collars.
He combined that with hand picking any visible cutworms off the soil surface. Another poster, Rubi, described a similar approach.
She checked the garden at night when cutworms are active on the surface and removed them by hand. Yogurt container collars protected her transplants the rest of the time.
Tilling soil a couple weeks before planting disrupts overwintering larvae early. Clearing weeds from the planting area one to two weeks ahead removes an early food source too.
That food source can otherwise support a growing cutworm population right up until transplants go in. For variegated cutworm specifically, collars alone will not stop a caterpillar climbing from above.
Watching for the distinctive W marking and irregular leaf or fruit damage helps catch that infestation before it spreads.
For a broader look at diagnosing which pest is behind a given symptom, see this site’s guide at what’s eating my tomatoes.
Frequently asked questions
How do you know if it was really a cutworm?
Cutworm damage shows a clean cut right at the soil line, sometimes with the severed top dragged into a nearby burrow. Rabbits cut at a 45 degree angle higher up the stem, and slugs leave chewed leaf edges rather than a clean cut, so the damage pattern is the best clue.
What do cutworms actually look like?
Smooth, hairless caterpillars, typically 1.5 to 2 inches long at maturity, in shades of gray, brown, black, or green. When disturbed, they curl into a tight C shape, which is one of the most reliable identifying traits.
Do cutworms only attack seedlings?
Most species do, cutting young transplants off at the soil line. Variegated cutworm is an exception, since it climbs established plants and feeds on upper leaves and fruit instead.
What actually stops cutworms from killing transplants?
Physical collars made from cardboard, foil, or cut down cups, pushed a couple inches into the soil around each transplant, are the most reliable defense. Tilling soil ahead of planting and hand picking visible cutworms at night both add further protection.
Can cutworms damage a tomato plant once it matures?
Usually not, except for variegated cutworm, which climbs mature plants and feeds on upper foliage and fruit rather than cutting stems at the base. Most other cutworm species lose interest once a stem toughens past the seedling stage.
Bottom line: cutworms on tomatoes deserve their reputation, but they also get blamed for damage caused by rabbits, slugs, and other pests more often than most gardeners realize. Checking the actual damage pattern, a clean cut at the soil line versus an angled bite or chewed leaf edges, is the fastest way to confirm the real culprit. Physical collars remain the most reliable defense, though variegated cutworm can still reach established plants by climbing instead of cutting.
Sources
Purdue University Vegetable Crops Hotline: Cut Seedlings and the Potential Culprits