Guide to Armyworms in MD and VA

Last updated: 09/28/2021
Estimated read time: 2.5 minutes

What are Armyworms?

Armyworms aren’t worms at all—rather, they are caterpillars of the armyworm moth. They are known to move in large numbers and quickly eat through their food supply, devouring grasses, grain crops, and more. To give you an idea of their speed—they can consume a football field in 2-3 days.

What do Armyworms look like?

In the larval stage, armyworms have yellow, red, brown, or green stripes along their sides and back and measure between 1.5 to 2 inches long. They are commonly spotted at dusk or in the early mornings. Once matured into moths, armyworms appear brown and dark gray with light and dark tones, though their underwings are a white/pale gray, with a wingspan of about 1.5 inches.

What are Fall Armyworms?

While armyworms appear in the spring, fall armyworms are a subspecies of armyworm that appears in the fall. They are slightly longer and darker in color, with white markings on their heads that look like an inverted “Y”. This image library by CABI Plantwise shows what fall armyworms look like throughout their lifecycle.

How can I tell if I have Armyworms?

Brown, discolored, or dying grass can be a sign of all sorts of lawn problems including summer patch and dollar spot and other common lawn diseases, grubs, drought stress, and improper lawn care just to name a few, however, there are generally more signs that appear when you have (or already suffered from) an armyworm infestation.

Signs You Have an Armyworm Infestation

  • Discolored grass that lays flat
  • Brown patches, especially along the perimeter, making their way inward
  • Chewed, jagged grass tips or transparent segments in grass blades
  • Bald spots, where they’ve eaten entire grass plants down to the soil
  • Increased or unusual bird activity on your lawn
  • Movement: Your lawn may look like it is moving on its own

What is the “Soap Test” for Armyworms?

The Soap Test uses a mixture of dish detergent and water, which is then poured on the weakest part of your lawn. The soap irritates the skin of the armyworm causing them to surface, making it easier to see and identify armyworms in your lawn. Here’s a quick video showing how to do the soap test on a small part of your lawn.

Where do I check for Armyworms?

Look at your property line, as well as uniformly across your yard. Armyworms will often move into areas from weeds along the edges and fence lines. As a result, applying treatment along the yard perimeters may be effective.

What does Armyworm Damage look like?

Armyworms are surface feeders. As they eat, the larvae leave ragged or transparent grass blades, brown or bare circular patches on the lawn, and may even crop your grass to the ground.

What kind of Grass do Armyworms eat?

Armyworms will devour a variety of grasses, including:

  • Bermuda grass
  • St. Augustine grass
  • Tall Fescue
  • Fine Fescue
  • Bluegrass
  • Ryegrass
  • Bentgrass
  • And more

Unfortunately, most grasses, like Ryegrass and Fescue, may not be able to recover after suffering an armyworm infestation. Some grasses, like actively growing Bermuda grass, may be able to recuperate, due to their aggressive growth habit.

Life Stages of an Armyworm

Armyworms have four distinct life stages: egg, larva, pupa, and adult.

After mating at night, the female armyworm can lay 100-200 eggs, which they attach to leaves. Newly hatched larvae feed on the leaf and eventually lower themselves to the turf to feed by spinning a silken thread.

Most defoliation will occur in the larva stage, where they will quickly consume more than 93% of the total foliage they will eat over their entire life span. Armyworm caterpillars will feed for two to four weeks before pupating in the soil. Fully developed moths appear about two to four weeks later.

How to prevent Armyworms

Here are some easy tips that can help you prevent armyworms from invading your lawn:

  • Aerate and seed your lawn every year.
  • Water your lawn deeply several times a week instead of frequent, light watering.
  • Mow your property to the proper height.
  • Fertilize your lawn, adding nutrients high in nitrogen.
  • Manually check for armyworm larvae and moths EVERY DAY.

Note that if you already have these insects in your yard, treatment is the only way to eliminate them. Our current treatment program is made up of two applications; however, our approach will be modified to best treat them as there are potentially multiple generations expected in our region.

How to get rid of Armyworms

The best way to eliminate armyworms is to use a targeted insecticide in infested areas, especially early on in the insects’ life cycle. Be sure to apply the treatment very carefully to avoid killing beneficial insects. To ensure success, we recommend reaching out to a professional lawn service company.

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