Cutworms are the larvae in caterpillar form of nocturnal moths. Even though these adult moths do not damage crops, the larvae often destroy young plants by eating the stems sitting nearest the soil. Because they can cut down young plants (especially seedlings) so quickly by biting through all of the plant's parts, they are called "cutworms."
Keep an eye out for cutworms on young tomato plants, asparagus, beans, cabbage, carrots, celery, corn, lettuce, peas, peppers, and potatoes. A few species do feed on turfgrass. Cutworms can damage lawns, too, but they prefer eating through huge swaths of manicured grass such as what you'd find at a golf range.
Are Cutworms Harmful to Gardens?
Black, bronzed, and army cutworms feed at night and hide in plant debris during the day. They can cause severe injuries to the vegetable plants mentioned above and to well-cared-for lawns. Meanwhile, the variegated cutworm climbs the stems of trees, shrubs, and vines, eating leaves, buds, and fruit. Glassy cutworms are one of several species that can stay in the soil and feed on the roots of new transplants and young plants, which they are fond of because the stems of these plants are more tender. Therefore, the damage is usually most serious in the early season, cutworms being most active in spring though still active in summer. Though cutworms are never consistent year to year, the higher the number, the more damage they will do to your plants.
Many people confuse cutworms and grubs because they tend to look somewhat similar with smooth, hairless bodies. Both insects also curl into a "C" shape when they are exposed. But you can tell cutworms apart from white grubs mostly because of their coloring and markings. Most cutworms are black, but they also present as brown, tan, pink, green, or gray. Some cutworms have spotted or striped patterns with either a dull or shiny coating.
How to Get Rid of Cutworms
When you find cutworms, don't delay in removing and protecting plants so the pests can't harm them further. Use these simple steps:
- Manually remove larvae from plants with your fingers or sterilized tweezers.
- Kill them by preparing a bucket of soapy water with liquid dish detergent and drop them into the water to drown. You can also crush them before drowning them.
- Build a 3- or 4-foot-high edge of dry soil to buffer your garden beds and prevent cutworms from entering the area.
- Take away any plant residue and weeds, both of which are attractive environments for young cutworm larvae to hide in during the day (some can survive in weeds through the winter).
- Use compost in your garden soil, not manure, because egg-laying tends to occur in green manure.
- Protect delicate transplants with 4-inch-wide collars made of cardboard, tin cans, aluminum foil, or toilet paper rolls. Insert an item so that about 2 inches can be placed down into the soil and the another 2 inches sits above the soil protecting the plant. That should be enough of a barrier to stop the cutworms from grabbing onto the plants.
- Catch cutworms with bait made by mixing Bacillus thuringiensis, molasses, and grain. Spread the bait on the soil near the affected plants and they will die from the fungus and become stuck in the molasses. The best contact insecticides for tomatoes contain cyhalothrin, esfenvalerate, and cypermethrin.
If you want to grow an organic garden, avoid using pesticides. Or, only apply evening doses of pesticide with carbaryl, cyfluthrin, and/or permethrin for climbing cutworms if there is a big infestation. If using on edible vegetation, make sure you don't use pesticide too close to harvesting time, but read the product's label for full directions.
Till your garden in autumn to kill any larvae or pupae in the soil. In the mornings, check plants while the damage would be fresh. Keep an eye out for plant remnants on the ground near their stems, plants cut off near the ground, or wilted plants, which are all signs of cutworm feedings. Confirm their presence by using a trowel to overturn any clumpy soil near the damaged plants. Exposed cutworms will curl into a "C." Some plants, such as tomatoes, peppers, and celery, will need to be checked regularly for cutworms from the time they're seedlings to maturity and harvest. Use beneficial nematodes in the garden since they will feed on cutworms and prevent their presence as well as other harmful insects.
Cutworms in Home Gardens. University of Minnesota Extension.
Control of Insect Pests In and Around the Home Lawn. Mississippi State University Extension Service.
Tomato Insect Pests. Clemson Cooperative Extension.