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How to Protect Seedlings From Cutworms in the Garden

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

Image Credit:
GrowVeg.com/Sam Droege on Flickr Creative Commons
Written By: Christopher Burnett Garden Writer

Cutworms can be a major annoyance in the garden, particularly for young seedlings or fresh 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 in 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—grey, pink, green, and black—and can be as long as 2 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, 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.

An adult moth of a brown cutworm.
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.

A black cutworm at the base of a damaged plant.
Black cutworms can cause severe injury to the base of plants, often killing them. Photo Credit: John Obermeyer, Purdue University.

Still unsure? Try our Plant Problem ID tool to quickly diagnose pests and diseases.

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.
  • Handpick 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 (DE), a natural powder made from ground up diatoms. When insects come into contact with DE, the fine powder gets within their exoskeleton and eventually dehydrates them.
    • Warning: Pollinators such as bees and butterflies are also susceptible to DE, so do not use it around flowers! Only place DE 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 (Bt), 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 of cutworms. Attract them to your garden by providing shelter (shrubs, trees) and water (bird baths)!

Garden Pests

About The Author

Christopher Burnett

Christopher Burnett

Garden Writer

Having grown up in rural New Hampshire, Chris has a great appreciation for all things outdoors, especially when it comes to native flora and fauna.Chris is an avid gardener, maintaining a small vegeta...

Read more from Christopher Burnett

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Comments

<span>Tricia Robinson</span> Fri, 05/08/2015 - 16:26
I have a problem with my yellow squash plants. after the plant matures and start putting off squash, something eats the root of the plant causing it to die. I've checked for cut worms, voles and anything thing else I can think of. But it only eats my squash plants, not the tomatoes, the beans, broccoli, peppers.....nothing but the squash. Any help would be greatly appreciated. Thank you.
<a title="View user profile." href="/author/editors">The Editors</a> Sat, 05/09/2015 - 02:34

It sounds like the dreaded squash borer. They overwinter in the soil, especially if you grew squash in the same place before. If you make a vertical slit in the stem with a sharp knife, you'll see them and can manually remove the larvae. Afterwards, mound soil over the stem to encourage re-rooting. Then you just have to see if your squash will recover. Unfortunately, at this point, most insecticides are not effective.

You can get ahead of squash borers by planting disease-resistant types,  using row covers (which you remove when it's time for pollination), starting planting earlier, and rotating crops.

 <span>Betty Penner</span> Mon, 06/25/2018 - 19:01
We had lots of problems with cutworms in our garden, until we put our wood ashes on the garden on the snow during the winter while cleaning out our outdoor wood furnace once in a while, spring came, and the snow melted, the ashes soaked into the ground, later we tilled it in, NO MORE CUT WORMS, but you can also sprinkle it on in the spring before tilling
<span>Cecilia Hamman</span> Thu, 04/23/2015 - 14:58
I planted broccoli, cauliflower, brussel sprouts, and cabbage about two weeks ago. All were cut down. I put out diatomaceous earth and corn meal and then replanted some broccoli yesterday with pencils stuck down beside them, plastic cups around them and diatomaceous earth around them. I went out after dark to check for worms and found none but went out today and almost all my plants were cut off. What can I do to stop them? This is a new garden spot that was in grass which I know makes them worse but there has to be a way to stop them! HELP!
<a title="View user profile." href="/author/editors">The Editors</a> Fri, 04/24/2015 - 15:53

Hi Cecilia,

The collars or cups that you put around the stems need to be pushed down a couple of inches into the soil so that the cutworms can't get under the collar. You can also try to wash the plants with a mix of bleach free dish soap and water. Also see the answer to the question from Karen below.

 <span>Karen Marriott</span> Sun, 04/19/2015 - 07:17
October last year we finished our drive laying new turf slabs at our front door and placing a new rubber backed mat down. Over the last few months when we have lifted our mat up there have been lots of black caterpillar/maggot like grubs underneath it. A large area of our lawn (next to the mat died. Yesterday we dug up that area ready to re-turf it and found lots of these grubs. Can you please offer me your thoughts on this and how you think I may eradicate the problem.
<a title="View user profile." href="/author/editors">The Editors</a> Mon, 04/20/2015 - 13:02

Hi Karen,

You probably have black cutworms. Read our tips above about how to get rid of them. There are a couple of biological control methods that you can try, parasitic nematodes and Bacillus thurbingiensis (Bt). You can read more about this at

http://entomology.osu.edu/bugdoc/Shetlar/factsheet/turf/Blackcutworm.htm

 

 

 <span>Nick Matu La</span> Thu, 04/09/2015 - 11:43
If you want to control a large area use Sevin granules. If you want to treat individual plants use Sevin 5% dust. Lightly dust around the base of each plant. Individually treating plants is preferred with dust so you dont kill everything in your yard...including your beneficial insects. Just a little dust at the base of each plant will work wonders. Read the label.
<span>Lynsee</span> Sat, 03/07/2015 - 10:50
We identified cutworms last spring in our garden. Our corn and bean seeds were not germinating evenly and we dug to find cutworms larva eating the seeds themselves. We also had several seedlings cut off at ground level. Our garden is now "bare" with no foliage and we would like to pretreat the soil to make sure the larva are dead. We live in Zone 6 so the ground is just beginning to thaw. Would you recommend tilling the soil and them spraying an insecticide? Please help! Thanks!
<span>Sasha</span> Sat, 03/28/2015 - 20:51
Get some beneficial nematodes! They will eat the larvae.