If you check on your garden and notice your tender young seedlings look like someone has taken a mini lawnmower to them, you may be dealing with cutworms. There are hundreds of species of cutworms, but basic control methods in the garden are the same for all types. Basic garden maintenance such as weeding, debris removal, vigilant monitoring and handpicking can help reduce cutworm damage. Beginning this process in early spring will have the most beneficial effect on young plants.
Identification: Cutworms are the caterpillar stage (larva) of a drab-looking group of moths that are often called miller moths. Cutworms are often brown or gray, but also come in colors such as green, black, tan and pink. They may be plain or patterned. These plump caterpillars measure 1 to 2 inches long when full grown. Cutworms feed at night and hide during the day. When disturbed, they curl up into a "C" shape.
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1. Controlling Weeds & Debris
Controlling weeds, grasses and plant debris both in and around the garden is an important preventive step because it reduces habitat and food favored by cutworms. Tilling the garden in early spring and fall can help kill cutworms or pupae or expose them to the weather and to predators such as birds.
2. Protecting New Plants
Transplants can be protected by making collars. A collar can be made of cardboard, stiff paper, plastic or aluminum foil. Wrap a collar around each stem extending it 1 to 2 inches into the soil and 2 to 3 inches above the soil. Tin cans with both ends removed can also make good collars to place over young plants.
Because cutworms need to completely encircle a stem in order to munch it off, placing a nail or a wooden stick right next to the stem is another tactic to stop damage.
Floating row covers or framed cages covered with screen door hardware cloth can be placed over developing plants and left in place through the growing season. These will keep cutworms out, but won't help with cutworms that may have overwintered in the garden soil.
3. Natural Predators
Natural enemies of cutworms include predators such as ground beetles, rove beetles, spiders, wasps, toads, parasitic nematodes and birds. Encouraging natural enemies can help keep cutworms under control.
Monitor the garden regularly to detect damage early on, especially in spring. If an early morning check finds a severed stalk or wilted plant (from a chewed on stem), turn over clumps of soil or carefully scratch in soil surface around the plants to search for a culprit or two. Some cutworms live in the soil, so you may need to carefully dig a little deeper. Early detection can help prevent severe nightly damage caused by some species, such as black cutworms.
Cutworms can be difficult to find during the day when they are hiding in the soil or under leaves. Handpicking can be much more effective if you go out at night with a flashlight when cutworms are active.
More About Cutworms
The telltale sign of a cutworm is a seedling stem that has been clipped off close to the soil surface. Usually the top part of the plant is left untouched, lying by the chewed-off stem. Cutworms eat all garden vegetables and they like flowers, as well. Cutworms especially like tender seedlings and young transplants. Spring plantings suffer the greatest damage. Some cutworms climb up plants to feed on buds, shoots and foliage. Leaf damage such as holes or ragged edges could be confused with slug damage, but if there is no slime trail, you may be dealing with cutworms.
The first moths emerge in May, or fly in from warmer climates in late spring. They lay their eggs in weedy areas, sometimes on the undersides of leaves. The eggs hatch within a week. The new cutworms start feeding on tender plants, often showing a strong preference for certain weeds or grasses. Cutworms can overwinter as pupae or larvae. Depending on the species, there can be one or more generations per year.
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- University of California Division of Agriculture and Natural Resources. Pests in gardens and landscapes: cutworms [Internet]. University of California Statewide Integrated Pest Management Program; 2019 [cited 2020 Jun 5]. Available from: http://www.ipm.ucdavis.edu/PMG/GARDEN/VEGES/PESTS/cutworm.html