What Do They Look Like?
Cutworms are the immature stage of a group of moths. Cutworms are fat, smooth, relatively large caterpillars, about 2-5 cm long. They curl up when disturbed. Some species are a dull, greasy grey, while others are green or tan with patterns of lines or dark markings.
Large yellow underwing moth, cutworms and typical leaf damage
The large yellow underwing moth is the latest cutworm to become a problem on the BC coast. The adult moth has dark brown forewings and apricot orange hindwings.
What Does Cutworm Damage Look Like?
All cutworms feed on plants at night. They hide in the soil or leaf litter near the base of plants during the day. There are two groups of cutworms: One group feeds on plant stems, just at or below the soil surface. Toppled seedlings and transplants snipped off at the soil line show where they are feeding. The most common cutworms in local gardens are the ‘climbing cutworms’, which includes the large yellow underwing moth. At night they chew large, ragged holes in leaves and new shoots. They can be particularly damaging to vegetable transplants, early shoots of potatoes and perennials.
Cutworm Life Cycles
In the mild coastal winter climbing cutworms often over-winter as caterpillars; some species over-winter as eggs. All species feed on plants in the spring for 3 weeks to 2 months. When full grown, cutworms change into an immobile stage, called a pupa, in the soil. Inside the pupa, the caterpillar transforms into a moth. Moths emerge later in the summer. Some lay eggs in the soil, while climbing cutworms lay eggs on branches, fence posts and other objects.
When Are Cutworms A Problem?
Cutworm numbers vary from year to year. When climbing cutworm numbers are high, they are particularly damaging to small plants between early May and late June. Large yellow underwing cutworms also feed on leaves of winter vegetables and other plants during warms spells in the winter.
How Can I Prevent Damage?
Turn soil several weeks before planting to allow birds to feed on cutworms. Set out transplants as late in the season as possible to avoid the main feeding period. Plant extra seeds or seedlings to ensure a normal crop after some losses from cutworms. Protect transplants from non-climbing cutworms by planting them with a protective “collar” around the stem. Make cylinders about 7-10 centimetres high and 5 centimetres across. You can make them from stiff plastic, light cardboard, toilet paper rolls or small metal cans with both ends removed. Push the cylinder at least 2 centimetres into the soil, with the rest extending above the soil. Protect the natural enemies of cutworms, such as birds, predatory wasps, parasitic wasps, ground beetles and other predators. Avoid using insecticides and attract beneficial insects by planting flowers that supply pollen and nectar (see the Beneficial Insects Info Sheets in the series).
What Can I Do To Control Cutworms?
Pick cutworms from plants at night or unearth them from around the base of damaged plants in the morning. Squash them or drown them in soapy water. This is sufficient to control cutworms in most gardens as there are usually only a few present. Microscopic worms, called nematodes, that attack insects are sold at some garden centres. They are expensive, but might be useful where cutworm numbers are unusually high or there is a large area to treat. Not all nematodes control cutworms, therefore before trying this approach, read product labels and talk to garden centre staff.
Tips For A Healthy Garden
© Image courtesy of L. Gilkeson
- Enrich the soil once or twice a year with compost or other organic fertilizers.
- Choose plants adapted to the conditions of sun or shade, moisture and soil acidity. If necessary, correct the drainage and acidity to suit the plants.
- Plant native plants, which are adapted to the local climate. Most are easy to care for and have few pest problems.
- Before buying plants, make sure they are healthy and free of diseases and insect pests.
- Water deeply, but infrequently, to encourage deep rooting.
- Cover the soil between plants and under shrubs with organic mulches. This insulates the soil, keeps in moisture and suppresses weeds.
- Protect and attract native beneficial insect, birds and other animals.