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Cutworms: How to Protect Seedlings from Cutworms | The Old Farmer's Almanac

Cutworms

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Black cutworms can wreak havoc on your garden, so learn these tips for identification and control.

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GrowVeg.com/Sam Droege on Flickr Creative Commons
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How to Protect Seedlings from Cutworms in the Garden

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Cutworms can be a major annoyance in the garden, particularly for young seedlings or transplants. Here’s how to identify, prevent, and get rid of cutworms in your garden.

What Are Cutworms?

“Cutworm” is the name used for the larvae of a number of moth species. The adult moths lay eggs on plant debris from spring through fall, with some species’ eggs hatching in spring and summer and others hatching in the fall. Those that hatch in the fall then overwinter in the soil or a woodpile, emerging in the spring to feast.

Cutworms do the most damage early in the gardening season, when they emerge from their winter slumber and feed on seedlings. Cutworms are caterpillars, but they are often mistaken for the grubs of beetles such as Japanese beetles (which are damaging in their own right).

Identification

How to Identify Cutworms

Cutworms feed on a wide variety of vegetables and flowers, so any young seedlings or transplants will be susceptible. To identify cutworms, try patrolling your garden at dusk or during the evening and inspect around the bases of plants. They are also partial to cloudy days.

Different species range in color from grey, pink, green and black and can be as long as two inches. They can be solid, spotted, or striped. They tend be curled up when they are not on the move. Cutworms are stealthy, and tend to feed only at night, hiding during daylight hours.

Black cutworms, Agrotis ipsilon, are one of the most common cutworms. They have small dark spots on their bodies and mature into the dark sword-grass moth.

Variegated cutworms, Peridroma saucia saucia, are another common species. They are mottled brown and have a faint white stripe down their backs.

Adult cutworms are moths of dark wing colors. They are usually brown or gray, and get to be about 1½ inches long with a 1½-inch wing length. Keep an eye out for the adults, because the females will lay eggs in dry soil after they mate.

Photo Credit: GrowVeg.com/gailhampshire on Flickr Creative Commons. The adult moth of the brown cutworm is an indicator that cutworm eggs could be in your soil.
The adult moth of the brown cutworm is an indicator that cutworm eggs could be in your soil. Photo Credit: GrowVeg.com/gailhampshire on Flickr Creative Commons.

Identifying Cutworm Damage

Cutworms chew through plant stems at the base. They primarily feed on roots and foliage of young plants, and will even cut off the plant from underneath the soil. In most cases, entire plants will be destroyed; they do a lot of damage in no time at all. Even if only the bottom of the plant is destroyed, the top will often shrivel and die.

In the summer, cutworms sometimes crawl to the tops of plants and do damage there. Be careful not to mistake this damage for slug or cabbage worm damage.

Photo Credit: John Obermeyer, Purdue University. Black cutworms can cause severe injury to the base of plants, often killing them.
Black cutworms can cause severe injury to the base of plants, often killing them. Photo Credit: John Obermeyer, Purdue University.
Control and Prevention

How to Protect Seedlings from Cutworms

Because cutworms can quickly do devastating damage to seedlings, prevention is key!

  • Make plant collars to protect stems. Encircle each stem with a 4-inch-tall piece of cardboard or aluminum foil to help stop cutworms from reaching tender stems, especially right after transplanting. This time-consuming task works, though it is only efficient for a smaller garden.
  • Hand pick cutworms off of plants. Go out at night with a flashlight and gloves. Pick off the cutworms and drop into soapy water; repeating this every few nights.
  • Surround stems with diatomaceous earth (D.E.), a natural powder made from ground up diatoms. When insects come into contact with D.E., the fine powder gets within their exoskeleton and eventually dehydrates them.
    • Warning: Pollinators such as bees and butterflies are also susceptible to D.E., so do not use it around flowers! Only place D.E. at the base of plants, where pollinators won’t encounter it. 
  • Apply an insecticide late in the afternoon for the best results. Some gardeners use Bacillus thuringiensis, a bacterium that affects soft-bodied insects and their larvae. 
  • Try this folk advice from The 1963 Old Farmer’s Almanac
    • A mulch of oak leaves is useful against cutworms.
    • Tansy planted near cabbages keeps them free of cutworms.
    • A hog turned into a garden in early spring will root up cutworms.

How to Prevent Cutworms Long-Term

  • In the spring, emerging cutworms will be waiting to feast on your garden. Cut off their food supply by delaying transplanting or planting by a couple weeks if possible.
  • Keep up with cultivation. The moths prefer to lay eggs in high grass and weeds. At the end of the season, plow or till the garden and mow surrounding areas to expose cutworms and destroy their winter habitat.
  • Beneficial insects, like parasitic wasps and green lacewings, will attack cutworms and other soft-bodied insects. Learn how to attract beneficial insects here!
  • Birds are another natural predator to cutworms. Learn how to make your garden bird-friendly.

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