How to get rid of cutworms and protect your transplants

You plant out your tomato seedlings in the evening. The next morning, two of them are lying on the ground, cut clean through at the soil line. That is the work of cutworms.

Cutworms are the caterpillars of several kinds of night-flying moths. They do the most damage in spring, when young transplants are small and tender.

How to identify cutworms

• Fat, smooth caterpillars, 1 to 2 inches (2.5 to 5 cm) long
• Gray, brown, tan, or greenish, sometimes with spots or stripes
• Curl into a tight C shape when you touch them
• Hide in the top inch or two of soil during the day
• Feed at night

Signs of cutworms

• Seedlings and transplants cut off at or right above the soil line
• Stems chewed partway through, so the plant wilts or falls over
• Holes in leaves and buds on some plants, from climbing cutworms
• Damage that shows up overnight

Cutworms attack many crops. Tomatoes, peppers, cabbage, broccoli, beans, lettuce, and flower transplants are common targets.

How to find cutworms

Look at the base of a cut plant. Dig with care through the top 1 to 2 inches (2.5 to 5 cm) of soil in a small circle around it. The cutworm is often curled up right there. Pick it out and drop it into soapy water.

You can also go out an hour or two after dark with a flashlight. Cutworms come up to feed at night.

How to stop cutworms

1. Put a collar around each transplant

A collar is the easiest way to protect transplants. Cutworms crawl along the soil surface and cannot get past it.

1. Cut toilet paper rolls, paper towel tubes, or cardboard strips into rings 3 to 4 inches (8 to 10 cm) tall.
2. Slide the ring over the transplant as you plant it.
3. Push the ring about 1 inch (2.5 cm) into the soil, so the rest stands above ground.

Leave the collars in place until the stems are thick and woody. Cardboard breaks down in the soil on its own.

Some gardeners push a toothpick or small nail into the soil right beside each stem. The idea is that the cutworm cannot wrap around the stem to chew it. Collars give you more protection.

2. Clear weeds before you plant

Cutworm moths lay their eggs in grassy, weedy ground. Clear weeds and grass from new beds at least 2 weeks before planting. That leaves the young cutworms with nothing to eat, so they starve or move on.

Be extra careful when you turn lawn into a new garden bed. Old sod is a common source of cutworms.

3. Turn the soil

Turning the top few inches of soil in fall and again in early spring exposes cutworms to birds and cold weather.

4. Plant bigger transplants

Thick, sturdy stems are harder to chew through. Grow strong seedlings and plant them out a little later, when stems are thicker. Here is how to harden off seedlings.

5. Use beneficial nematodes

Beneficial nematodes are tiny worms that hunt cutworms in the soil. The species Steinernema carpocapsae is sold for cutworm control. Apply them to moist soil in the evening and water them in, since sunlight kills them.

6. Spray Bt for climbing cutworms

Some cutworms climb up and eat leaves and buds. Bt (Bacillus thuringiensis var. kurstaki) kills caterpillars that eat treated leaves. Spray in the evening. It does not harm people, pets, bees, or ladybugs.

Natural enemies

Birds, toads, ground beetles, and parasitic wasps all eat cutworms. Avoid broad-spectrum insecticides, which kill these helpers. Here is more on beneficial insects that eat garden pests.

More help for transplants

• How to grow tomatoes
• How to grow peppers from seed to harvest
• How to grow broccoli
• How to get rid of slugs in the garden
• How to get rid of earwigs