How to Get Rid of Armyworms Like a Pro

Some common causes of brown patches on your lawn include drought stress, dog urine, disease, or burning from too much sun or fertilizers. Armyworm caterpillars are a less common culprit. However, these cool-season grass lovers can cause widespread lawn damage when left unchecked. 

We spoke with an entomologist to learn how to get rid of armyworms so your lawn stays looking lush.

What are Armyworms?

Armyworms are larvae (caterpillars) of moths that can be grass and crop pests. The true armyworm (Mythimna unipuncta) and the fall armyworm (Spodoptera frugiperda) are two common types in North America.

True armyworms have a large dark spot at the bottom of their abdominal prolegs and an orange line down each side of their body. Fall armyworms have a distinctive white “Y” on their heads.

Dr. Tracy Ellis, an award-winning entomologist at FarmSense, says that the easiest way to know if you have fall armyworm is if you see noticeably damaged patches on an otherwise good-looking lawn in the late summer and fall. 

Dr. Ellis says armyworms are big lovers of a wide range of grasses, including popular Bermuda grass, Kentucky bluegrass, switchgrass, buffalo grass, and zoysia grass. They also feed on some edible garden crops, ornamental plants, and weeds.

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How to Get Rid of Armyworms: 4 Methods

Before implementing any control measures to get rid of armyworms, Dr. Ellis says you need to confirm you’re dealing with these garden pests.

Regularly inspect your lawn or other plants prone to armyworm damage. Early detection and prompt action minimize damage, making it easier to get rid of infestations without resorting to harsh chemical control methods.

“A soap drench test may be used to bring hidden insects to the surface and determine if the fall armyworm is the culprit,” Dr. Ellis says.

She suggests mixing 1 oz of quality liquid dish soap per gallon of water.

“Use a couple of gallons to pour over one square yard of lawn,” she says. “Take photos of the insects found by the soap drench test to show your local extension service or pest control service.”

As well as looking for distinguishing features on the caterpillars, Dr. Ellis says you might notice the mother of the fall armyworm—a gray-brownish moth with a 1.5-inch wingspan, hovering over lawns and host plants during humid evenings in the summer. Setting up moth traps can also help prevent armyworm larvae from being laid.

Below are four strategies for getting rid of armyworms.

Weed Your Landscape

Keep your lawn, flower beds, and vegetable plot weed-free.

“Weeds are potential harborages for eggs and young armyworm larvae,” Dr. Ellis says.

Plus, she explains that many weeds can feature in armyworm diets, including pigweed, dandelion, buttonweed, sow thistle, nightshade, crabgrass, and more.

Tilling sites can also help to control weeds and destroy armyworm pupae overwintering in the soil.

Apply Reduced-Risk Organic Control Products

Organic insecticides for controlling armyworms are less harmful to the environment and beneficial creatures in your yard than broad-spectrum chemical products.

Those containing the active ingredient Bacillus thuringiensis (Bt) have a bacterium that studies show is effective when consumed by young armyworms less than 1/2-inch long.

Entomopathogenic Steinernema carpocapsae nematodes are microscopic worms that can kill off armyworm larvae and pupae populations without harming people or pets.

It’s easy to apply beneficial nematodes using a watering can or a sprayer at rates advised by manufacturers.

Encourage Beneficial Predatory Insects

By avoiding broad-spectrum insecticides and growing a diverse range of plant species, you can encourage natural armyworm enemies to help prevent numbers from exploding. 

Stink bugs, big-eyed bugs, ground beetles, rove beetles, tachinid flies, some types of assassin bugs (Rhynocoris segmentarius), and parasitic wasps are some beneficial insects that lay eggs on or eat armyworms.

Apply Chemical Control Products

Only consider harsher chemical control of armyworms as a last resort, when infestations are out of control and cultural and biological methods have been unsuccessful. Even then, it can be challenging because of insecticide resistance development in armyworm populations. 

Products registered as safe for use on armyworms can vary by state, and some are restricted-use and can only be applied by a licensed applicator. Dr. Ellis advises to only use methods recommended by your local extension service or a pest control professional.

Chemical insecticides that can help control armyworms include those containing the active ingredients bifenthrin, cypermethrin, carbaryl, cyfluthrin, deltamethrin, and permethrin.