Armyworms: What are they, how they can tear up yards, and how to combat them

Alabama News

Armyworms are becoming a problem across north Alabama again and they can wreak havoc on plants of all kinds – including a typical homeowner’s lawns.

The Alabama Cooperative Extension System said they’ve been an issue for crops across the Southeast for more than 100 years.

But they attack and damage much more than crops; they attack turf and a variety of common grasses – bermudagrass being the most common.

Armyworm Lifecycle

Female moths lay eggs on light-colored surfaces in masses of up to several hundred; look for light gray, fuzzy eggs.

As the eggs mature, they darken, eventually hatching 2-4 days later.

The hatched caterpillars remain in the egg mass shortly after hatching and spin down to the turf on silk webs – look for light-colored, black-headed larvae at this stage.

As they grow, their bodies get darker and stripes appear. When fully grown, the larvae are between 1.25 and 1.5 inches long with several stripes along their body; colors range from light green to almost black.

The face of the worm can be spotted easily – look for a light-colored, inverted Y-shape – and the body segments have four spots each with the last four arranged in a square.

The lifecycle from egg to fully grown caterpillar takes around 2-3 weeks. At that point, the caterpillar burrows into the ground and lies dormant for 10-14 days.

The moth then emerges from the ground, feeds on nectar, and lives for around 10 days.

It’s possible to have four or more generations of the armyworm each year, given the short lifecycle, but ACES said only one usually causes visible lawn and turf damage.

Most of the north Alabama armyworms come from populations that spend the winter months in southern Florida and Texas; the moths are carried to north Alabama on high-altitude winds.

While local armyworms attempt to survive the winter by burrowing into the ground, they can’t survive the frigid north Alabama winters.

  • As they grow, armyworm caterpillars get darker and stripes appear. When fully grown, the caterpillars are between 1.25 and 1.5 inches long with several stripes along their body; colors range from light green to almost black.
  • Female moths lay eggs on light-colored surfaces in masses of up to several hundred; look for light gray, fuzzy eggs.
  • The hatched caterpillars remain in the egg mass shortly after hatching and spin down to the turf on silk webs - look for light-colored, black-headed larvae at this stage.

What to Look For

ACES stated the best way to see armyworm caterpillars is to look for them “marching” in large numbers across a lawn – they are generally easy to see.

They feed openly and in a very conspicuous manner, chewing through plant tissue primarily in the early morning or late afternoon/early evening hours; however, ACES cautioned that they can be active any time of day.

The adult fall armyworm is an ash-gray moth with a wingspan of about 1.5 inches. the front wings are smaller with a mottled gray and brown color, with the large, back wings being white with a narrow, smoky brown edge.

Like most moths, they become active at twilight and may be seen at porch lights – they sometimes blend in and are difficult to see at all.

ACES said just because moths are around, however, doesn’t indicate an outbreak of larvae.

Eggs can be found on light-colored surfaces such as the undersides of leaves, metal gutters, fence posts, light-colored lawn furniture, and goal posts (specifically the underside of a football goal post’s crossbar).

Signs of a possible infestation

If there’s no visible lawn damage, one indication of a possible infestation is a large presence of birds and paper (red) wasps feeding in the same area.

Birds may peck holes in turf looking for caterpillars and wasps kill the caterpillars, kneading them into a ball before feeding them to wasp larvae. Fire ants may also overwhelm and kill caterpillars.

If birds and wasps are feeding in the same area, visually check for caterpillars.

If none are found, check for green pellets or consider doing a soap flush to bring the caterpillars to the surface: Mix two tablespoons of liquid dish soap in one gallon of water; pour the mix over an area of one to two square feet.

Caterpillars, if they’re in the yard, will emerge from the soil.

How to treat for armyworms

If mowing, do it before treating the lawn. Powdered insecticides can be moved or removed from a lawn by mowers.

The best time to treat for armyworms is in the early or later hours of the day, when armyworms are the most active.

Products to treat armyworms aren’t normally labeled for armyworms, but for caterpillar pests.

Examples include powdered formulas such as Bayer Advanced 24 Hour Grub Killer Plus and Hi-Yield Turf Ranger Insect Control or ready-to-use sprays such as Thuricide and Bioadvanced Complete Insect Killer.

ACES reminds homeowners to consult the label for lawn care instructions after applying the insecticide.

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