Experts say Bacillus thuringiensis, beneficial nematodes, pyrethroids and chlorantraniliprole insecticides are some of the best methods to get rid of armyworms in your lawn.
The fall armyworm outbreak in 2021 caused major damage to farmers and homeowners. In September 2024, Ohio State University released a new armyworm alert. Learn what insecticides to use and when so you’re always ready to keep armyworms at bay.
What Are Armyworms?
Armyworms are the larval stage of adult moths and a common lawn pest in the United States. These caterpillars feed on many plants, including flowers, fruit, and grass. They attack fast, in large army-like colonies, damaging entire lawns overnight. Armyworms do most of their damage in summer to early fall.
The term armyworm can refer to different species of caterpillars. Fall armyworm (Spodoptera frugiperda) causes the most damage. Other species include the beet armyworm, yellow-striped armyworm, and true armyworm.
If armyworms are in your lawn you’ll find egg masses on turfgrass and surfaces near the lawn (patios, walls, fences, trees, flags, plants, etc.) and larvae in the thatch layer. Learn more about how they look and their lifecycle from out article, “What Are Armyworms?”
Signs of armyworm damage to look for include:
- Brown patches and brown spots
- Ragged blades
- Lacy or transparent blades
- Bare soil
Pay special attention to armyworm presence if you recently installed sod. “If you planted new sod, the sod is likely under stress and releases stress signals to attract FAW (fall armyworms), resulting in infestation,” explains Dr. Shimat Joseph, associate professor of Turfgrass and Ornamentals in the Department of Entomology at the University of Georgia.
How to Get Rid of Armyworms Naturally
The best solution is always prevention. To prevent armyworms from making a feast in your grass, keep your lawn healthy, water it properly (not too much, not too little), and don’t allow the thatch to build up. Here’s more on “How to Prevent Armyworms”.
You can pick and choose which of the following methods work best for you, but we recommend always combining the chosen method with proper lawn care, especially lawn mowing.
1. Handpick the Armyworms
- When to use: In all larval stages. Most helpful for large larvae, easy to see and grab.
Pick the armyworms one by one from the grass canopy. Prepare a bucket with a gallon of water and a teaspoonful of a dish soap of your choice, and throw all the armyworms you have managed to pick into the bucket. The soap will kill all of them within minutes.
Handpicking is an eco-friendly pest control method that works best on small infestations.
2. Use Armyworm Natural Enemies
- When to use: Support their presence year-round.
Ladybugs, lacewings, and minute pirate bugs feed on armyworm eggs and young larvae. Trichogramma wasps are parasitic wasps that lay their eggs inside fall armyworm larvae, killing them from within.
To attract and support these beneficial insects: Add flowering plants that provide pollen and nectar around your lawn. Avoid spreading synthetic insecticides unless necessary to protect these beneficial insects and support their activity.
If you need to buy and release: Place the container with the insects in areas with a large population of armyworms. Release the insects in the early evening. Spritz the surrounding vegetation with a mist of water.
3. Apply Bacillus Thuringiensis
- When to use: Most effective on young larvae. Apply within a week after spotting egg masses.
In order to work as a biological insecticide, Bt must be eaten by the insect. Inside the insect, Bt toxins bind to the gut wall, and cause its cells to break apart. Within minutes of eating Bt, the insect stops feeding.
Bt can kill the armyworm in its larval stage within 48 hours of ingestion. The specific strains that target armyworms are Bt aizawai and Bt kurstaki.
Pro tip: Direct sunlight inactivates Bt, so spread the solution in the late afternoon.
Bacillus Thuringiensis bacteria can also be used to control cutworms, sod webworms, beetles, and the larvae of mosquitoes.
4. Introduce Beneficial Nematodes
- When to use: Most effective in small infestations.
Beneficial nematodes are microscopic worms that eat armyworms from the inside out, leaving only their empty shells. Common species that target armyworms include Steinernema carpocapsae and Heterorhabditis bacteriophora.
In order for nematodes to be effective, it’s important to be handled properly all the way from the provider to the application. They “need to be obtained from a reliable source for good product quality, as they are living organisms that can be killed by heat, desiccation and UV radiation,“ says Dr. Shaohui Wu, assistant professor of Turfgrass Health in the Departments of Entomology and Plant Pathology at the Ohio State University.
Pro tip: Apply early morning, late afternoon, or on an overcast day (nematodes are sensitive to sunlight).
Do not use beneficial nematodes combined with beneficial insects since they can also prey on those insects.
5. Spread Organic Azadirachtin Insecticides or Neem Oil
- When to use: Most effective on young larvae. Apply within a week after spotting egg masses.
Azadirachtin is a substance found in the seeds of the neem tree. It’s primarily an antifeedant, but it also disrupts normal insect growth, repels larvae and adults, sterilizes adults and deters egg laying. You can find it as an active ingredient in organic insecticides such as Azatin (OMRI certified).
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Can you use neem oil? Dr. Wu specifies that neem oil needs to contain azadirachtin to be effective (not all products in stored do). Look for 100% or 70% neem oil labeled as insecticide or fungicide.
How to Get Rid of Armyworms with Synthetic Products
Using organic, natural insecticides is always better. However, overwhelming armyworm infestations in late summer or fall might require insecticide applications.
Synthetic pesticides are designed to kill only certain types of pests, so they usually don’t harm animals or plants if appropriately used. However, always read the label carefully to know precisely how to apply the insecticide and what it will do to your yard or garden.
Most pesticides require you to wear protective clothing and gloves and keep children and pets away from the treated area until it has dried completely.
1. Pyrethroid Insecticides
When to use: Most effective on younger larvae.
These pyrethroid insecticides kill the larvae quickly upon contact. Do band applications around the structures where you spot eggs and larvae. Look for products with these ingredients:
- Permethrin – Durvet Permethrin 10%
- Deltamethrin – Bayer Suspend
- Bifenthrin – Compare-N-Save 7.9% Bifenthrin Concentrate for Insect Control
There’s a catch though: Some pyrethroid insecticides require a license. You might need a pro’s help to take care of this application.
2. Chlorantraniliprole Insecticides
When to use: Effective against armyworms of all sizes. Also works as a preventive.
“Once caterpillars increase in size, chlorantraniliprole insecticide might be the best option,” says Dr. Joseph.
Chlorantraniliprole is a systemic insecticide classified in the toxicity category IV: non-toxic and not an irritant. It can also be used to control grubs and Japanese beetles.
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Some pesticides are more toxic than others, and some have been banned in the United States. If you have questions about what chemicals are safe for your family, talk to your local pest control expert.
FAQ About Armyworms
What time of day is best to spray for armyworms?
Insecticides are best applied in early morning or late evening. It’s when armyworm activity it’s the most intense and these destructive pests are more likely to be exposed to the substance.
How Often to Spray for Armyworms?
To control armyworms, you usually need to spray at least two times. However, the number of applications depends on the insecticide you use, the stage in the armyworm development, and the time of year.
Will grass come back after armyworms?
Most grass types will come back after armyworm infestation, but not immediately. You will have to take good care of your lawn. Treating the soil with nitrogen fertilizer might help the grass grow back quickly.
Can You Wait It Out?
As a farmer, no, but as the average homeowner, sometimes you can. Despite their voracity and significant damage, armyworms are considered minor lawn pests because they rarely kill grass plants. They do leave the crowns exposed, and some might dry out in the heat of the summer, but generally, turf recovers in time with lawn fertilizer and proper watering.
When to Hire a Professional
Taking care of a large number of armyworms on your lawn by yourself can be a lot of work, but you don’t have to win this battle alone. If you are not feeling up to the task, hire a professional. Find a lawn care pro near you who can take this burden off your back!
Sources:
- Joseph, S.V. (2024, August 18). Fall armyworm: Biology and Management in Georgia Turfgrass. University of Georgia Extension. https://site.caes.uga.edu/entomologyresearch/2024/08/fall-armyworm-in-georgia-biology-and-management-in-turfgrass/
- Joseph, S.V., Hudson, W.G., Waltz, C. (2018, May 10). Armyworms in Sod. University of Georgia Extension. https://extension.uga.edu/publications/detail.html?number=C1130&title=armyworms-in-sod
- Kujawski, R. (2011) Bacillus thuringiensis (B.t.). UMass Extension Landscape, Nursery, and Urban Forestry Program.
- Shetlar, D., Wu, S. (2024, September 4). Fall Armyworm Alert! Ohio State University. https://buckeyeturf.osu.edu/news/fall-armyworm-alert
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