- Cutworms get their name because they cut down young plants as they feed on stems.
- There are climbing cutworms that move up plants and feed on foliage, buds and shoots.
- Seedlings are most susceptible to cutworm feeding.
- Physical removal is effective in many cases.
- There are pesticide options if cutworm problems are severe.
How to identify cutworms
Cutworms are similar in general appearance. They are smooth with very few hairs and are about two inches when fully grown. They typically curl into a tight 'C' shape when disturbed.
Different species 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.
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.
Some cutworm species, including variegated and black cutworm, migrate into Minnesota from the south each year. However, dingy, bronzed, and glassy cutworms are native to Minnesota and overwinter as eggs or larvae in weedy or grassy areas. Moths mate and lay eggs from early spring (black cutworm) to late summer or fall (dingy, glassy and bronzed cutworm).
- Female moths can lay hundreds of eggs, one at a time or in small clusters.
- Eggs are deposited on or near low-growing plants and plant residue.
- Weed seedlings are also an attractive egg-laying site for cutworm moths.
- Young larvae feed on leaves or small roots until they reach about 1/2 inch in length, when they move on to seedling stems by cutting or burrowing through them.
- The number of cutworms is controlled by weather, especially rainfall.
- They may go through three generations per year.
Damage caused by cutworms
Cutworms are general feeders that can attack a wide range of plants. Common vegetables they like to feed on include asparagus, beans, cabbage and other crucifers, carrots, celery, corn, lettuce, peas, peppers, potatoes and tomatoes. A few species feed on turfgrass.
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. The number of cutworms found can vary a lot each year. When their numbers are high, there can be severe damage to a garden.
- Black, bronzed and army cutworms can cause serious injuries, attacking and cutting new plants nightly.
- The 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.
- 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.
- Adult moths do not damage plants.
How to protect your plants from cutworms
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 your garden for cutworms in the 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.
Change the garden environment
Remove plant residue to help reduce egg-laying sites.
- Remove weeds, which serve as an alternate host for young cutworm larvae.
- 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 can be applied to the stems or leaves (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. Be sure that the plant you wish to treat is listed on the label of the pesticide you intend to use. And observe the number of days between pesticide application and when you can harvest your crop. Remember, the label is the law.
Reviewed in 2019