Cutworms are killed by biological pesticides, beneficial insects, parasitic nematodes, synthetic insecticides, and simple physical methods like soil tilling and cardboard collars. The best approach depends on the size of your problem and whether you’re protecting a home garden or a larger planting. Most cutworm damage happens at night, when larvae emerge from the soil to chew through seedling stems at ground level, so nearly every control method works better when applied in the evening.
Bt: The Most Effective Biological Killer
Bacillus thuringiensis (Bt) is a naturally occurring soil bacterium that produces proteins lethal to caterpillars, including cutworms. When a cutworm eats plant material coated with Bt, the proteins dissolve in its gut, punch holes through the gut lining, and allow bacteria to flood into the body cavity. The larva stops feeding within hours and dies from internal infection, usually within a day or two. Bt is sold as a spray or dust at most garden centers and is approved for organic use.
Bt only works when larvae ingest it, so thorough coverage on plant surfaces matters. It breaks down in sunlight within a few days, which means you’ll need to reapply after rain or every week or so during active cutworm season. Because it targets the caterpillar digestive system specifically, it won’t harm bees, earthworms, or pets.
Beneficial Nematodes
Microscopic roundworms in the species Steinernema carpocapsae are particularly effective against cutworms. These nematodes actively hunt soil-dwelling larvae, enter through natural body openings, and release bacteria that kill the host within 24 to 48 hours. You apply them by mixing a packet of nematodes into water and spraying or watering the solution into the soil.
Soil conditions make or break this method. Nematodes need soil temperatures between 70°F and 85°F to stay active, and the soil must remain moist for at least two weeks after application. Time your treatment with rain or plan to irrigate before and after. Applying in the early evening helps, since nematodes are sensitive to UV light and dry conditions.
Natural Predators That Help
Several ground-dwelling beetles are voracious cutworm predators. Species like Pterostichus melanarius and Poecilus cupreus are among the most aggressive, returning repeatedly to attack prey even after initial contact. Ground beetles are most active at night, which lines up perfectly with cutworm feeding behavior. You can encourage beetle populations by leaving some ground cover or mulch strips near garden beds and reducing broad-spectrum pesticide use.
Birds, particularly robins, starlings, and crows, also eat cutworms when tilling exposes them. Parasitic wasps and tachinid flies lay eggs on or in cutworm larvae, and their developing young consume the host from within. None of these predators will eliminate a heavy infestation on their own, but they provide meaningful ongoing suppression.
Tilling and Soil Cultivation
Turning the soil is one of the simplest ways to kill cutworms. Tilling exposes overwintering pupae and larvae to cold, drying, and predators like birds. For the best results, till at least two weeks before planting. This destroys plant residue that harbors larvae and gives exposed pupae time to die before your seedlings go in.
Fall tilling is especially valuable if you’re following a crop that cutworms favor, like beans, alfalfa, or legume cover crops. Kill and remove weeds before planting too, since cutworms shelter in both living and dead plant material. Keep in mind that if pupae are already established deep in the soil, removing surface plants alone may not prevent damage.
Cardboard Collars and Physical Barriers
A stiff cardboard or paper collar around each seedling stem physically blocks cutworms from reaching the plant. The collar should extend 1 inch above the soil surface and 2 inches below ground, with about half an inch of clearance around the stem. An empty paper towel roll cut to size works well. This is one of the most reliable methods for small gardens, since it requires no chemicals and protects plants 24 hours a day.
For larger plantings, this becomes impractical, but for a dozen tomato transplants or a row of peppers, collars take only a few minutes to install and last the few weeks that seedlings are most vulnerable.
Poisoned Bran Bait
A classic cutworm bait combines dry wheat bran with molasses and a pesticide, scattered around the base of plants in the evening. The molasses attracts cutworms, and they consume the poisoned bran instead of your seedlings. A traditional small-batch recipe calls for 1 pound of toxicant mixed into a peck (about 8 quarts) of dry bran, 1 pint of molasses, and 2 to 4 quarts of water, stirred until evenly coated. Letting the mash sit for several hours before spreading it can improve effectiveness.
Apply bait in the late afternoon or early evening, since cutworms feed almost exclusively at night and burrow into the soil during the day. If cutworms are migrating into your garden from adjacent grass or weedy areas, running a narrow band of bait along that border can intercept them. Modern commercial cutworm baits use safer active ingredients than the arsenic-based formulas of older agricultural bulletins, so look for products labeled specifically for cutworm control at garden supply stores.
Synthetic Insecticides
When damage is heavy, synthetic insecticides offer the fastest knockdown. The most common options fall into a few chemical families. Pyrethroids (the active ingredients in products containing bifenthrin, permethrin, or lambda-cyhalothrin) kill cutworms on contact and work as curative treatments after you’ve spotted damage. Diamide insecticides like chlorantraniliprole are unusual in that they work both as a preventive and a curative treatment, meaning you can apply them before cutworms appear.
Carbaryl (sold under the brand name Sevin) is one of the most widely recognized cutworm killers for home use. It works best against species that feed on the upper portions of plants rather than those that cut stems at ground level. A few practical timing notes: apply in the evening when cutworms are active, avoid irrigating treated areas for at least 24 hours after application, and stay off treated surfaces until sprays have dried. Applying within two hours of sunset also reduces risk to bees.
Diatomaceous Earth
Diatomaceous earth (DE) is a powder made from fossilized algae that damages the waxy outer coating of soft-bodied insects, causing them to dehydrate. It can kill cutworms that crawl through it, but it has a significant limitation: it destroys all soft-bodied insects, including beneficial ones like ground beetles and predatory larvae. It also loses effectiveness the moment it gets wet, so you’ll need to reapply after every rain or irrigation. DE is a reasonable last resort for small areas but not a first choice if you’re trying to preserve the beneficial insects that provide long-term cutworm control.
How Bad Is the Damage Before You Treat?
Not every cutworm sighting justifies reaching for a pesticide. In corn, the standard threshold is 2 to 3 percent of plants cut or wilted when larvae are still small (under three-quarters of an inch). That threshold rises to 5 percent if the larvae are larger, since bigger cutworms are closer to pupating and will stop feeding soon. When crop prices are high, some growers lower the trigger to just 1 percent of plants showing damage.
In a home garden, the math is simpler: if you’re losing seedlings nightly, it’s time to act. Check for cutworms by digging gently around the base of damaged plants in the morning. The larvae curl into a C-shape and hide an inch or two below the surface. Handpicking in the early morning is surprisingly effective for small gardens, especially when combined with collars on your remaining transplants.