What are fall armyworms?

Fall armyworms are the caterpillars of a migratory moth that moves north through Florida each year. They get their name from the way large groups march across turf and crops, eating as they go. Northeast Florida typically sees them from late summer into fall.

How fast do fall armyworms damage a lawn?

Fast. Extension research notes that caterpillars consume the large majority of their food in the final few days of the larval stage, so an outbreak can go from unnoticed to stripped turf in under a week. That is why scouting matters as soon as ragged patches appear.

What do fall armyworms look like?

The caterpillars grow to about an inch and a half, range from green to nearly black, and carry light stripes running down the body. The reliable field mark is a pale, upside-down Y shape on the head capsule.

Which grasses do fall armyworms eat?

Bermuda grass is the favorite, but high populations also feed on St. Augustine, Zoysia and other turf. Lawns that are lush and well-fertilized tend to attract egg-laying moths first.

How do I check my lawn for armyworms?

Scout at the edge of damaged areas early in the morning or late in the evening. For a faster answer, mix one to two tablespoons of dish soap into a gallon of water and pour it over a square yard of turf at the damage border. Caterpillars come to the surface within minutes.

Do fall armyworms come back every year?

The moths migrate north each season, so pressure varies year to year. Outbreak years often follow active tropical weather, which carries moths into the area. A lawn that had armyworms once is not immune to future waves.

Fall Armyworms in Northeast Florida: ID, Damage & First Steps

Short answer: Fall armyworms are migratory caterpillars that arrive in Northeast Florida from late summer into fall, often after tropical systems, and can strip a lawn in days because most of their feeding happens in the final days of the larval stage. Look for a fast-advancing ragged edge, caterpillars with a pale upside-down Y on the head, and birds working the lawn at midday. Confirm with a soap flush at the damage border, then treat quickly if counts are high.

Watching a Brown Front Move Across Your Lawn?

Speed matters with armyworms. RightWay can confirm what is feeding, treat active infestations and monitor the lawn through the rest of the season. Share your address and what you are seeing.

Request a Lawn Review Call (904) 290-6400

Why Northeast Florida Gets Armyworm Waves in the Fall

Fall armyworm moths do not overwinter in numbers this far north. Each season they migrate up from southern Florida and the Gulf, riding weather systems, and each generation pushes farther. By late summer and fall, the waves reach the Jacksonville and St. Augustine area, which is exactly when local lawns are at their most lush.

Tropical storms act like a delivery service. Moths survive surprisingly well on the wind, and outbreak years here frequently follow an active storm stretch. If a system passed through two or three weeks ago and your lawn suddenly looks scorched, armyworms deserve to be the first suspect checked.

lawn pest control in jacksonville fl, armyworm treatment in st augustine fl, lawn care in st johns county fl — A fall armyworm caterpillar. The pale, upside-down Y on the head is the field mark that separates it from other lawn caterpillars. (Photo: Frank Peairs, Colorado State University, Bugwood.org, via Wikimedia Commons, CC BY 3.0 US)

How to Identify Fall Armyworms

The caterpillars grow to about an inch and a half and range from light green to nearly black, with pale stripes running the length of the body. Color varies enough that it is not the reliable mark. The reliable mark is on the head: a pale, inverted Y. If you can see that Y, you have an armyworm.

Behavior is the second clue. Fall armyworms feed day and night, so a lawn being actively chewed at noon points away from night-feeding caterpillars like sod webworms. Clusters of birds picking through the grass in daylight often mark exactly where the feeding front is.

A Moving Front

Damage starts as a ragged edge and advances like a front across the lawn, sometimes visibly from day to day, as the caterpillars march and feed.

A Mowed-Down Look

Heavily hit areas look scalped or scorched: grass blades chewed to the crown in patches, with only stems left behind.

After-Storm Timing

Local outbreaks frequently show up one to three weeks after tropical systems pass through, when migrating moths arrive on the wind.

Daytime Feeders

Unlike sod webworms, which feed only at night, armyworms keep eating through the day. Birds working your lawn at noon are often feeding on them.

armyworm control in jacksonville fl, lawn treatment in ponte vedra fl, lawn pest control in st johns county fl — An armyworm feeding on a grass blade. Large larvae do the vast majority of the eating, which is why damage accelerates so suddenly. (Photo: शीतल सिन्हा, via Wikimedia Commons, CC BY-SA 4.0)

Scouting: The Five-Minute Soap Flush Test

You do not have to take a guess from the color of the damage. A simple soap flush brings caterpillars to the surface so you can count them:

Go out early in the morning or near dusk, when armyworms feed most actively, and start at the edge between healthy and damaged turf.
Mix one to two tablespoons of lemon-free dish soap into a gallon of water.
Pour the mix slowly over about a square yard of turf at the damage border.
Watch for two to five minutes. Caterpillars irritated by the soap wriggle to the surface, which gives you a count and a look at their size.
Check two or three spots. Several caterpillars per square yard in an actively spreading patch means it is time to treat, not wait.

One thing not to do: mow and hope. Mowing does not reach caterpillars hiding at the base of the grass, and a healthy feeding front keeps advancing. Confirm first, then treat the cause.

Armyworm or Sod Webworm? A 30-Second Check

Sod webworms are the other common lawn caterpillar in our area, and the two get confused constantly. The differences change how urgent the situation is:

Clue	Fall Armyworm	Sod Webworm
Active when	Day and night, heaviest morning and evening	Night only; hides in thatch by day
Head marking	Pale, upside-down Y on the head	No Y; darker spotted body
Damage style	Fast-moving front that can strip large areas	Smaller scalloped patches that spread slowly
Peak season locally	Late summer and fall, often after storms	Summer through early fall

While you are checking the damage border, it is also worth ruling out grub worms, which attack roots below the surface and leave turf that peels back like carpet instead of blades chewed to the crown.

Local Lawn Help From RightWay

RightWay's lawn fertilization, weed control and lawn-pest service includes monitoring for exactly this kind of fast-moving pest activity, so outbreaks get caught at the edge instead of after the lawn is stripped. Homeowners can also review service information for Jacksonville Beaches, Ponte Vedra Beach and other St. Johns County communities.

Service is available in selected Northeast Florida communities. Contact RightWay through the quote form or call 904-290-6400 with your address and a description of the damage.

Fall Armyworms in Northeast Florida: Identification, Damage and First Steps