Do transparent grass blades, chewed leaves, and brown patches seem like they appeared in your lawn overnight? They might be signs of armyworm damage, a common pest of home lawns and golf courses.
Armyworm damage is easy to confuse with drought signs and the damage done by lawn diseases and other pests, so in this article, we tell you what is specific to these nasty caterpillars and how to check for their presence.
Main Characteristics of Armyworm Damage
Armyworms are the larvae of several moth species from the genus Spodoptera and Mythimna in the Nuptiade family. While the moths are harmless to your lawn, the armyworm larvae are voracious foliar pests.
Armyworm caterpillars feed primarily on plant leaves, removing grass blades from their stems. They might also chew on the stems (especially of young, juicy grass) but rarely eat the crowns and never attack the grass roots.
When munching on turfgrass armyworms:
- Leave transparent spots on the blades
- Feed on the leaf tips and margins, creating ragged holes around the blade
- Eat all the tender grass leaves and leave behind only the stems
- Move fast – damage appears overnight
Armyworms damage is most severe from August to October when their population reaches larger numbers.
Note: Armyworm damage is easily confused with cutworm infestations. However, there are a few differences to keep in mind:
- Cutworm damage is more spread across the lawn, with less well-defined areas.
- Cutworms love to munch on stems, crowns, and roots and sever the plants before eating them. It’s rare to see grass plants with munched leaves still standing.
5 Ways to Tell You Have Armyworms in Your Lawn
Turf that Looks “Frosted”
If you have armyworms, your lawn might look “frosted” in the infested areas. Newly hatched armyworm larvae are not strong enough to feed through a grass leaf. They munch on the underside of the blade but leave the top layer intact.
If you pick up a grass blade like this, you’ll notice transparent spots, like tiny silver or white window panes. When the larvae are in large numbers, “the grass often has a subtle ‘frosted’ appearance because of these window panes,” says Dr. Blake Layton, Extension Professor at Mississippi State University.
Flat, Discolored Grass
Flat and discolored grass can be caused by water stress and compacted soil but can also be a sign of armyworm presence.
Plants munched on by armyworms are less able to keep their shape and tend to lie toward the soil, creating areas that look like a steamroller passed over. If you see this in your lawn, check the leaves for transparent spots and signs of chewing.
Well-Defined Brown Patches
Homeowners who don’t pay much attention to their lawns might not notice the problem until brown patches grow on their turf. The brown circular or oval spots resemble those caused by drought, excessive heat, brown patch disease, dog urine, lawn grubs, or chinch bugs. Pretty standard, right? So, how do you know it’s armyworms? Here’s how.
Brown patches caused by armyworm caterpillars first appear around the perimeter or near structures where moths can lay their eggs (fences, light posts, patios, trees, sheds, etc.), and later in the center of the lawn.
The patches appear overnight and are also pretty neat and well-defined.
“Since armyworms cross the turf surface as a group, they create a noticeable line between damaged and undamaged turfgrass,” explain North Carolina University Extension experts.
Chewed Leaves and Cut Stems
Leaf damage done by armyworms is pretty specific. If you take a closer look at the grass, you’ll notice that turfgrass leaves have transparent spots or ragged edges around the brown patch, and they look chewed and torn. In the middle, grass stems are cut off close to the ground, and the area has a scalped or scorched appearance.
Not sure it’s armyworms browning your lawn? Read our guide, “Why Does My Lawn Have Brown Spots?” to identify the cause.
Birds and Rodents Hunting for Food
Insects and animals alike are attracted by food. Armyworms come into your yard for the grass, and birds, bats, skunks, and rodents come for the armyworms. You should suspect a pest infestation if these natural predators are hunting on your lawn.
However, since they feed on many lawn pests (grubs, cutworms, sod webworms, etc.), use the other infestation signs we discussed before to determine whether it’s armyworms or something else. Or, start actively scouting for the villain.
How to Detect Armyworms
Scout for Egg Masses
Egg masses look like whitish, fuzzy patches up to 1 inch across. Homeowners often find them on structures near the lawn, such as fences, light posts, sheds, patios, outdoor furniture, exterior house walls, flags, etc. Remember to check tree trunks, broadleaf weeds, and ornamentals nearby.
Getting rid of egg masses before they hatch is an excellent way to keep armyworms at bay. Our guide, “How to Prevent Armyworm Infestation,” offers more pest control methods to help you stop these invaders.
Look for Armyworms in Turfgrass
Take a look around the lawn. Armyworms are active in the turf canopy in the early morning and late evening or during the day when the weather is cool and cloudy. Some might even stick to your shoes on a wet, dewy morning.
You might also notice armyworm droppings, which look like small green or yellow “square” hay bales, 1 to 2 mm long, on the leaves or at the base of the grass plants in damaged areas.
Use the Soap Test to Draw Them Out
When it’s hot and sunny, armyworms often hide lower in the grass or go down close to the ground and hide in fallen leaves, thatch, grass clippings, or loose soil.
To flush them out, mix 2 tablespoons of dish soap with 1 gallon of water and pour the solution on a 1 square foot of damaged lawn – if armyworms are there, they’ll surface in a few minutes. Read our guide “What Are Armyworms?” to make sure you know what they look like.
FAQ About Signs of Armyworm Damage
What Attracts Armyworms to Your Lawn?
Armyworm moths are attracted to areas suitable for nesting: moist and with plenty of food. Succulent, young turfgrass in newly installed lawns is especially prone to infestations. Moths are also attracted by light.
How Long Do Armyworms Stay Around?
Armyworms go through life cycles lasting 30 to 60 days, from egg to moth. However, more than one generation can infest your lawn, and without treatment, armyworms can stay around until a freeze comes along and kills them.
What Kills Armyworms?
Armyworms can be killed by natural predators such as parasitic wasps, ground beetles, birds, or biological insecticides with bacteria (Bacillus Thuringiensis) or beneficial nematodes. You can also eliminate armyworms by applying synthetic insecticides such as products with pyrethroids or chlorantraniliprole.
Save Your Lawn from Munching Pests
If you ignore their presence, armyworms can munch an entire lawn in a few days. Act fast when you spot signs of armyworm damage. Find a pest control professional with LawnStarter and protect your turfgrass from hungry caterpillar pests!
Want a break from the lawn care routine? LawnStarter professionals can also mow, aerate, dethatch, remove fallen leaves, and take care of all the daunting lawn tasks you dread. Your free time is only a few clicks away!
Sources:
- Billeisen, T., Brandenburg, R. (2017, October 25). Fall Armyworms in Turf. North Carolina State University Extension
- Knutson, A. (2018, September). Texas A&M AgriLife Extension. The Fall Armyworm – A Pest of Pasture and Hay. https://lubbock.tamu.edu/files/2018/09/Armyworm-Fact-Sheet-2018.pdf
- Layton, B. (n.d.).Fall Armyworms in Hayfields and Pastures. Mississippi State University Extension Service. http://extension.msstate.edu/publications/fall-armyworms-hayfields-and-pastures
Main Image Credit: NokHoOkNoi / Adobe Stock / License
