Cutworm Control: How To Treat Cutworms In The Vegetable Garden

The term “cutworm” is used to describe several different types of caterpillars.

These caterpillars metamorphose into common moths known as Miller (Noctuid) moths and lay eggs in garden soil and debris.

In autumn, the eggs hatch and the larvae dwell in the soil until springtime when they wreak great havoc on many different kinds of crops.

In this article we describe the different types of cutworms you may encounter in the garden and in your lawn.

We also share tips to help you keep these pests under control. Read on to learn more.

How To Tell One Cutworm From Another?

Cutworms are often subject to mistaken identity because many people believe them to be grubs, but they are not.

They are ground-dwelling caterpillars and are active at night.

Because of this, you may not be aware of their presence in your garden until they begin to damage your plants.

Sometimes, cutworm damage is masked by army worm and looper caterpillar damage. Making this mistake is easy if you have a large daytime caterpillar population.

You may also mistakenly think cutworm damage to plant leaves has been caused by slugs.

In this case, treating for slugs will do nothing to deter cutworms. Be sure to properly identify your pest before taking steps to deter it.

The best way to determine whether or not your garden has cutworms is to patrol with a flashlight at dusk and during the evening hours.

These critters come out to feed when it’s dark. You may also see them on cool, overcast days.

3 Of The Most Damaging Types of Cut Worms

Three of the most damaging types of the many varieties of cut worms are:

Peridroma saucia (variegated cutworm)

These are a dark, mottled brown color with a light white stripe on the back.

Alternately, variegated cutworms may be grayish with dark brown speckles and single rows of light yellow dots on the sides.

Agrotis ipsilon (black cutworm)

These pests are dark with small, dark spots. They grow up to be sword-grass moths.

Amathes c-nigrum (spotted cutworm)

This cutworm is a dull, grayish-brown color with dark stripes on each side and wedge-shaped markings below the stripe, near the back of the body.

These three types of cutworms look different but have similar habits.

They can all be found plaguing potato plants. In fact, they can have devastating financial effects on commercial potato crops.

In addition to these, there are quite a few other species which range greatly in size, patterns and colors. Some can be as big as 2” – inches long.

They come in striped, spotted and solid varieties in shades of black, gray, green and pink.

Even with these variations, you can tell you have found a cutworm when you see a pest curling into a “C” shape in the dirt during the day.

Furthermore, these creatures all have very smooth skin appearing to be greasy or wet. Their bodies are quite plump.

For a good pictorial guide to many varieties of cutworm, here

In the evening, you can find cut worms near the surface of the soil, or see them crawling on your plants.

During the day, just turn a few trowels of the earth in your garden, and you may find these culprits curled up in a tight circle waiting out the heat of the day.

Agrotis ipsilon close up
Agrotis ipsilon via Wikimedia Commons

How To Identify Miller Moths?

These drab, night-flying moths are usually dark gray or brown. They typically measure about an inch and a half long from snout to tail with a wingspan of about three inches.

You may see the females fluttering around your garden soil in the evening looking for a place to lay eggs.

What Is The Life Cycle Of A Cutworm?

Most Miller moths produce one generation annually. The eggs or young larvae over-winter in the soil or in leaf litter.

The eggs hatch in early spring, and the caterpillars begin feeding overnight right away.

They typically target native plants and weeds first while waiting for cultivated crops to emerge.

Eggs or small larvae may overwinter in soil and especially tend to do so in areas where grass has grown in the past.

The caterpillars emerge from the soil in the springtime and begin to feed.

When they reach full size, they go back to the soil and dig a little chamber where they pupate.

Pupae may develop over the winter or early in the spring. When the pupae mature, adult moths emerge.

The moths, in themselves, are not damaging. They just fly around in the evening seeking light and mates.

After mating, the females lay eggs in the soil during the late afternoon or during the night.

Some types of Miller moths lay single eggs. Others lay small clusters of eggs.

Those from variegated cutworms lay large clusters of more than six-hundred eggs, arranged in neat, tightly packed rows.

The eggs are hemispherical and quite small. You can usually find them in the soil or under leaf litter on the ground.

In some settings, female Miller moths lay eggs on the stems and leaves of plants.

The incubation period ranges from a couple of days to a couple of weeks. This is determined by the type of moth and also by the ambient temperature.

The life cycle of all types of cutworms is fairly similar and varies a bit in terms of time.

The variegated cutworm develops most rapidly, and it is possible for as many as four generations to be produced per season. Most of the others only produce a single generation per season.

How Do Cutworms Damage Plants?

The worst damage cutworms do is chewing through the base of a plant’s stem. This kills off the entire plant, even if only a small amount of the plant is eaten.

The cutworms also eat plants’ roots and tubers when they are very small and still underground.

Early on, cutworm damage may manifest as damage to just a few smaller, weaker plants in the garden. If you deal with the cutworms quickly, you may be able to divert further damage.

If left to grow larger, the caterpillars tend to climb up plants and feast on leaves. When this happens, you will see ragged cut-outs and holes in the plant leaves.

If the cutworm population is small, this damage can be minor, but if there are lots of cutworms in residence during midseason, the results can be devastating.

Mid-season, plants can only tolerate about 10% defoliation. If there is a large population of more mature cutworms at this time, a great deal of damage can be done. Fortunately, foliar damage usually occurs later in the season when plants can tolerate more leaf loss.

What Plants Do Cutworms Attack?

The plants most affected by cutworms include:

  • Cabbage
  • Lettuce
  • Beans
  • Corn

Do Cutworms Eat Tomatoes?

Very early in the growing season, small cutworms can wreak havoc on young tomato plants by cutting them off at ground level.

As the plants and caterpillars mature, damage to leaves is likely. These pests will also make holes in the fruit.

This is especially true if tomatoes are allowed to come in contact with the soil.

How To Eradicate Tomato Worms Naturally?

Prevent cutworms from ever getting a foothold by removing any plant residue from the soil when you till.

Keep surrounding areas well trimmed, tilled and mulched (with oak leaves).

Till a minimum of two weeks before planting any crop to ensure that cutworms at any stage of development are rooted out and exposed.

This is especially important when planting tomatoes in an area previously planted with a very attractive cover crop, such as beans, alfalfa or legumes.

Do Cutworms Eat Grass?

Female Miller moths will lay eggs in grass, and the emerging caterpillars do eat grass.

To determine whether or not you have a cutworm problem in your lawn, flush them out with a mild soap solution. This also works for army worms and a number of other soil-dwelling pests.

In most cases, the soap solution both flushes them out and kills them.

How Do You Control And Prevent Cutworms?

There are lots of non-pesticidal ways to deal with cutworms. Use these 16 simple tips singly or in combination to keep cutworms “baffled” and discouraged.

Add Plant Collars

If you find cutworms bothering plants after you transplant them, make a 4″ – inch cardboard collar to wrap around the base of each plant.

Press it into the ground a bit so the cutworms cannot simply slip under it. This is a time-consuming task, but if you only have a few plants, it will work well.

Plant With A Collar

When you start seeds indoors, use empty toilet paper tubes or paper towel tubes cut in half, as seed starting pots.

Arrange the tubes on end, tightly in a tray. Fill them with seed starting mix and add seeds. When transplanting, include the tube.

Be sure the tube is sticking up out of the ground by 4″ – inches or so to deter cutworm predation.

Pluck Them Off

When patrolling with your flashlight at night, be sure to carry along a bucket of soapy water. When you see a cutworm, pick it up and drop it into the bucket.

Use Eggshells or Coffee To Make It Rough

Sprinkle crushed eggshells and/or used coffee grounds around your plants making it unpleasant for cutworms to crawl.

Use Diatomaceous Earth

Diatomaceous Earth is natural mineral powder is effective against all manner of insects. Sprinkle DE on the ground around your plants.

When cutworms and other pests walk across it, it will coat their undersides and desiccate them.

Apply Bacillus thuringiensis (Bt)

This natural bacterium (Bacillus thuringiensis)is very effective against all sorts of caterpillars (including good ones).

To be sure of targeting cutworms, apply (Bt) to the soil and very low on plants at dusk.

Use Natural Mulch

Cutworms don’t like oak leaves. Mulching your garden with chopped up oak leaves helps deter them and also helps conserve water and nourish the soil.

Try Companion Planting

Cutworms dislike tansy, so planting it among your other plants can help protect them.

Use Pigs Or Chickens

If you are a small homesteader, enlist the aid of your pigs and/or chickens to help till your garden early in the springtime.

As they root and scratch about, they will find and eat cutworms and other ground-dwelling pests.

Starve Them

Delay your planting by a couple of weeks to starve cutworms waiting in the soil. Be sure there are no weeds or other types of plants around to stave them over.

Trim and Till

Don’t allow grass and weeds grow high around your garden.

Keep grass mowed, and till up soil frequently to prevent giving cutworms a chance to become established.

Be sure to till at the end of the growing season to expose any cutworms waiting to overwinter in your garden.

Plan Ahead

If you have a patch of grass you plan to cultivate next spring, go ahead and plow it before winter.

This is especially important if you plan to plant potatoes.

Having the plowed area stand through the winter will kill off any cutworms and eggs lurking in the soil.

Enlist Parasitic Insects

Encourage Tachinid flies and parasitic wasps to live in your garden. Both are very effective at controlling cutworm populations.

Encourage Fireflies

Add charm and defense to your garden with these natural cutworm predators.

Fireflies like yards with a small water source, natural pine trees and a source of light at night. Fireflies are also attracted to undisturbed wood piles, so set up a small, extra pile of wood just for them.

Any cutworms deciding to take up residence in the woodpile will quickly become a tasty treat.

Attract Toads and Terrapins

All of the things that attract fireflies will also attract toads and terrapins, and they love to eat caterpillars of all sorts.

Introduce Nematodes

Check with your local garden center for natural nematodes to add to your garden soil. They make short work of cutworms and many other soil dwelling pests.

Avoid using chemical treatments to deal with cutworms as this is very bad for the soil and the water table.

With so many natural ways to deal with these pests, the use of chemicals is entirely unnecessary.

Do Birds Eat Cutworms?

Having birds in your yard and garden is always a plus, and they certainly enjoy cutworms and many other pests.

If you provide bird baths and set out feeders, you will quickly invite a yard full of activity and song.

The birds you might think of as “undesirable” are actually your best friends when it comes to caterpillar control.

Welcome blackbirds, blue jays, sparrows and wrens as they all do a great job of patrolling for and consuming cutworms.

Other wild partners who can help reduce your cutworm population include moles and skunks.

Even though you might not think of them as desirable, keep in mind that they are usually active at night (when cutworms are active) so you are unlikely to encounter them.

Does Sevin Kill Cutworms?

If your garden does experience a sudden, overwhelming infestation, you may need to use a pesticide, such as Sevin in a controlled manner.

Any time you resort to a pesticide, try to use it sparingly and keep concerns about water, air and soil quality in mind.

Read and follow all packaging and label instructions carefully.

Below are 3 pesticides considered as effective controls against cutworms.

Sevin or Carbaryl is quite dangerous to pollinators, such as bees and butterflies.

If you must use Sevin, spray it sparingly on the ground around affected plants. Apply it at dusk to avoid affecting positive pollinators active in the daytime.

Lannate or Methomyl can be used late in the season if you see cutworms attacking your plants’ fruit.

It is best to apply it to the soil surrounding the plants and to the fruits and leaves at the lower levels of the plants.

Note: Using this product may actually increase populations of other pests, such as leaf-miners and plant lice because it kills off their natural predators.

Use it very carefully, if at all.

Bacillus thuringiensis (Bt) is also called Spinosad. Spinosad spray is a natural bacterium works by exploding caterpillars’ stomachs.

It is best to use it very early in the season right after eggs hatch. Under heavy infestation, you may need to apply it a couple of times over the course of 7 to 10 days.

It is best not to use chemicals on a regular basis. However, if you do, rotate them so pests don’t build up a resistance.

How To Decide When And How To Treat For Cutworms?

Generally speaking, if you cultivate a natural garden rich in natural helpers, predatory and parasitic insects along with nematodes and make regular use of natural deterrents, you should never have to make a conscious decision to deal with these common pests.

Even so, monitor your garden closely for these and all manner of invaders.

Early detection enables quick, small, effective intervention.

Very often, cutworms only attack one small area, so you don’t need to treat your whole garden.

Just isolate the area, remove affected plants, treat and transplant new plants.

Sources:

  • https://cropwatch.unl.edu/potato/cutworms
  • https://www.ndsu.edu/pubweb/pulse-info/Cutworms.html
  • http://ipm.ucanr.edu/PMG/r783301511.html