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How to Control Cutworms in Your Garden

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If your starters or transplants are being lopped off at the base, the likely culprit is cutworms.

By Jessica Dawe Posted Apr 12, 2016

Cutworm

If it is Spring where you live, it is likely a fat little grub curled up like the letter “C” is sleeping in your garden soil going unnoticed until the damage is done. The cutworm larvae are likely responsible for the early demise of your freshly planted starts and seedlings. The destructive feeding behavior of this grub clear-cuts young seedlings at the base, leaving toppled, partially eaten tops. They come by their moniker of “Cutworm” honestly. The range of this lepidoptera is species dependent, but reaches from southern Mexico to the 51st parallel in Canada.

The who’s who

Adult cutworm moth
There are three types of cutworm moth that are especially common in North America. The number of generations they have depends on location of the pest. North Carolina, for example, can see as many as 4 generations/year, while in Florida there may be 5 – 6 generation/year. In the warmer climate zones of Canada, gardeners can see 2-3 generations of cutworms per year.

  • The Black Cutworm Agrotis ipsilon is a serious pest of corn and does not overwinter in the colder climes of the U.S. The adult moths arrive in these locations via the strong southerly winds from the Gulf states and Mexico travelling a few hundred miles in just a couple of nights. The adults will lay their eggs on the leaves of weeds or crop residue prior to late corn being planted. They will feed on the leaves of host weeds until corn shoots emerge at which time they will move to the crop and eventually burrow into the soil to tunnel into the stalk. Early detection is the best defense. Keep an eye out in springtime for the adults arriving on the wind and inspect corn plants for wilt or damage. In small gardens it is very helpful to pick the cutworms by hand if you find them.
  • The Variegated Cutworm (Pearly Underwing) Peridroma saucia has the widest distribution in North America. Their range includes southern Canada from coast to coast, the entire US, and all the way south into Mexico. Variegated cutworms overwinter as grubs in the soil and are most distinguishable by the 5 yellow dots along the center of their back. They emerge in early spring for the newly emerging first growth. They will initially feed on weed hosts until the plants they favor emerge. Vegetable hosts include asparagus, bean, cabbage and other crucifers, carrot, celery, corn, lettuce, pea, pepper, potato, rhubarb, and tomato. As with the Black Cutworm, early detection is essential because they arrive so early. If you see a freshly fallen starter, dig an inch or so into the nearby soil and you’ll likely find the culprit.
  • The Spotted Cutworm is most common in the Gulf States and scattered as far north as North Carolina, and has recently been discovered as a pest of mint crops in Oregon. The spotted cutworm only has 2 generations per year throughout the US.

Looking for larvae

Cutworm
The larvae of this pest is abundant in early spring, you may have already seen them if you have been preparing your garden beds lately. Really, they are hard to miss. Very fat, grey/brown/black caterpillars about 1- 1 3/4” long found just beneath the soil surface. One might even say they look peaceful when discovered. Curled up, sleeping like the animated caterpillar varieties of Disney. Don’t let their sleepy persona deceive you. If you were to return later that night with flashlight in hand you would discover them mowing down the succulent growth in their path.

As with the nocturnal adults, the strategy of the juvenile cutworm caterpillar is to hide during the day when ambitious parasitic wasps, tachinid flies and other predators are actively hunting. At night the cutworm larvae have the protection of darkness. This does not make them unmanageable, only a bit more of a challenge to control. Much success in controlling cutworms has been achieved through the attraction of native beneficial predators. There are many of these insects already in your garden and they include cutworms as part of their diet. To encourage these beneficial insects to establish a residence in your garden, it would be helpful to include these plants:

Predator/ParasiteCompanion Plants
Ground BeetleCreeping thyme, scotts moss, sedums, ornamental grasses
Tachinid fliesQueen Annes Lace, cilantro, dill, coriander, buckwheat, clover
Parasitic waspsOrnamental allium, alyssum, campanula, shasta daisy, chives, mint

Using nematodes to control cutworms

Insect parasitized by nematodes
A beneficial nematode is a microscopic predatory worm that uses the cutworm caterpillar as the ideal spot to lay their eggs. Though nematodes are tiny they are highly effective at sourcing prey. When they find a suitable host they enter through the mouth or anus and they release a bacteria that rapidly decomposes the pest within 24-48 hours providing food for the developing nematode juveniles. Native to most healthy soils and safe for people to use, these biological controls can be purchased easily by the homeowner and applied using a watering can.

Mechanical controls for keeping cutworms in check

There are a number of mechanical controls you can take to reduce the cutworm population in your garden. These have the benefit of being chemical-free and nontoxic.

  • Trees and buffers. In combination with protecting moths blowing in on wind currents, forested areas provide habitat for the multitude of beneficial insects that feed on cutworm larvae and moths. Birds, ground beetles and parasitic wasps need the diverse habitat that a hedgerow can offer as protection to the surrounding area. If your garden does not have a “wild zone”, it might be something to consider in your over all garden strategy.
  • Tillage. Turn the soil in the morning (early bird gets the worm), once in the fall and lightly again in the spring prior to planting to expose a meal to the native birds and predators
  • Remove weedy areas weeks before planting to eliminate alternate hosts
  • Weed in and around garden for discovery and exposure.
  • Wide barriers between lawn and bed
  • Use stem barriers. Using recycled plastic cups or milk cartons, place barrier around the stem of the plant. Sink it in at least 1- 2” into soil.

The time is now!

If the Forsythia in your neighborhood is blooming then now is the time to start looking for cutworms in your garden. Scouting for the larvae in the soil and monitoring when the adults are flying will give you the best advantage of staying ahead of the game. Hand picking them out of the soil goes a long way towards control and also provides a tasty morsel your chickens will appreciate. If you are feeling overrun and unable to keep up with the populations, then add nematodes to your soil for ongoing effectiveness. Cutworms don’t have to be a pest for you, but if left unchecked can ruin an entire crop overnight.

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Jessica Dawe owns a garden center and has been practicing integrated pest management and permaculture since graduating in 1995 with a degree in horticulture.
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  • Casey

    Has anyone tried using diatomaceous earth against cutworms? Is it effective? Some people recommend DE but I’m worried about it killing beneficial insects in the garden. Plus it washes away easily…

    • We use DE around starters to help control slugs and sow bugs, but it’s hard to know if it is effective against cutworms.

  • Farmer

    Years ago – I won’t say how many, my Dad religiously planted tomatoes using a “cup” made from tar paper. He simply planted the young tomatoes then rolled a piece of tar paper about 3 or 4 inches in diameter around the stem and buried it a couple inches deep. Goodby cut worms!

    • Interesting, thanks for your comment. We use a similar approach, using small squares of roofing felt (thick tar paper) and cut a slit to fit around the stem. They lie flat on the ground around the base of the stem.

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