Quick facts about cutworms
Cutworms are the larvae (caterpillars) of several species of night-flying moths in the family Noctuidae. The larvae are called cutworms because they cut down young plants as they feed on stems at or below the soil surface.
- The adults are night-flying moths and do not cause damage.
- There are also species of climbing cutworms that move up plants and feed on foliage, buds and shoots.
- Cutworms attack a variety of plants like asparagus, bean, cabbage and other crucifers, carrot, celery, corn, lettuce, pea, pepper, potato and tomato.
- A few species also feed on turfgrass.
- Frequently check your gardens for insects before they multiply rapidly and cause severe damage.
How to identify cutworms
Cutworms can look different from one another and they can range in color from brown or tan to pink, green or gray and black.
- Some cutworms are a uniform color while others are spotted or striped.
- Some larvae are dull and others appear glossy or shiny.
- Cutworm larvae will grow to a two-inch length.
- Cutworms curl up into a tight "C" when disturbed.
Life cycle of cutworms
Some cutworms migrate into the state from the south each year. But, other species, like dingy cutworm, bronzed cutworm and glassy cutworm are native to Minnesota in weedy areas, grassy fields or pastures and live through the winter as eggs or larvae.
Female moths can lay hundreds of eggs, one at a time or in small clusters.
- They deposit eggs on low-growing plants and plant residue.
- Migrating moths lay eggs on the soil and the larvae hatch to feed on plants.
- Young larvae feed on leaves or small roots until they reach about 1/2 inch in length. Eggs and larvae may be seen on young weeds.
- Larvae start feeding on seedling stems, by cutting or burrowing through them.
- Cutworms may survive on weeds, through mild fall and winter seasons and attack vegetables in the spring.
The number of cutworms are controlled by weather, especially rainfall. Moths mate and lay eggs from early spring (black cutworm) to late summer/fall (dingy, glassy, and bronzed cutworm), beginning the next generation. They may go through three generations per year.
Common cutworm species in Minnesota
The most common species of cutworm occurring in Minnesota gardens are the bronzed cutworm, variegated cutworm, black cutworm, dingy cutworm, glassy cutworm and army cutworm.
Adult moths are moderate sized, brown or black insects showing various splotches, or stripes in shades of gray, brown, black or white.
- They generally have a body length of about one inch with wingspans up to 1 1/2 inches across.
- Typically, the front wings are darker than the hind wings and are patterned.
Damage caused by cutworms
Cutworms curl their bodies around the stem and feed on it. This feeding causes the plant to be cut off just above the soil surface.
- Some cutworms, e.g. black, bronzed and army cutworms, can be very injurious, attacking and cutting new plants nightly.
- Climbing species of cutworm, (e.g., variegated cutworm) can climb the stem of trees, shrubs, vines and garden plants and eat the leaves, buds and fruit.
- Species such as glassy cutworms, remain in the soil and feed upon roots and underground parts of the plant.
The number of cutworms found can vary a lot each year. When their numbers are high, there can be severe damage to a garden.
- Cutworms feed in the evening or night and hide in plant debris during the day.
- New transplants or young plants have more chances of injury because their stems are more tender.
- Damage is most severe in the early season, when plants are small and have tender tissue.
- Cutworms are active throughout the summer, but are rarely a problem after spring.
How to protect your plants from cutworms
Identify the damage on time
Check for damage
Check your plants in the morning when damage is fresh and easier to see.
- Watch for plants cut off near the ground or plants that are wilting (when cutworms chew on the stems but do not sever the plant).
- If you see droppings on the ground, it is a sign of cutworm feeding.
Check for cutworms
Check your garden during late afternoon and evening when cutworms are more active.
- To confirm that cutworms are present, run your hand over the soil, rolling over soil clumps and other potential hiding places, within one foot of the damage.
- If cutworms are present, they will curl up into a “C”, when disturbed.
Control of cutworms is more effective when the larvae are small. For some crops, such as tomatoes, peppers and celery, you may need to monitor for cutworms until harvest.
If damage or larvae are discovered, you can:
- physically remove and crush or drop the insects into soapy water
- maintain a three to four foot buffer of dry soil along the edge of the garden to make it unattractive to cutworms
Remove weeds to reduce egg laying sites
- Remove plant residue to help reduce egg-laying sites.
- Remove weeds that nourish small cutworms.
- Till your garden before planting which helps expose and kill larvae (that have lived through the winter).
- Use compost instead of green manure as manure may encourage egg laying. Till your garden in the fall to destroy larvae or pupae in the soil.
Use a barrier to keep cutworms out
- Place aluminum foil or cardboard collars around transplants. This creates a barrier that stops cutworm larvae from feeding on plants.
Place the collars around plants such that one end is pushed a few inches into the soil, and the other end extends several inches above ground. This should prevent most species of cutworms from getting to your plants.
Pesticides are usually not necessary in the home garden. If there is a severe problem, pesticide should be applied to the stems or foliage (for climbing cutworms).
It is best to apply product in the evening, before the cutworms come out for feeding. Examples of common pesticides effective against cutworms are carbaryl, cyfluthrin and permethrin.
CAUTION: Mention of a pesticide or use of a pesticide label is for educational purposes only. Always follow the pesticide label directions attached to the pesticide container you are using. Remember, the label is the law.
Be sure that the vegetable you wish to treat is listed on the label of the pesticide you intend to use. Also be sure to observe the number of days between pesticide application and when you can harvest your crop.
Reviewed in 2018