A fall armyworm infestation does not look like a slow decline. A lawn that looked fine on Friday can be brown and shredded by Monday. Alabama Extension calls them “voracious feeders” that “can consume large quantities of foliage in a short time.”
The good news is that they are easy to find if you look, and cheap to stop if you catch them early. Almost all the damage people suffer comes from not looking.
When to start watching
Extension’s guidance: moths arrive in central Alabama in April and May, and “in most years during late July or early August, reports of fall armyworms on turf begin,” with earlier reports out of south Alabama. Occasionally severe outbreaks turn up as early as mid-April.
For Tuscaloosa, that means scouting from mid-July through the first frost — which NOAA normals put around November 10 at the airport station.
A complicating detail: the life cycle takes roughly 30 days, so multiple overlapping generations can be active at once. Extension reported during the August 2024 outbreak that heat was compressing generations to about 25 days, causing flights to overlap and stack up.
Who gets hit
Bermudagrass, and particularly well-fertilized bermudagrass. Extension’s home lawn insect guide notes the preference directly. If you push nitrogen on a bermuda lawn, you have built exactly what they are looking for.
How to check: the soap flush
This is the standard Extension scouting method and it takes five minutes.
- Mix two tablespoons of liquid dish soap into one gallon of water.
- Pour it slowly over a one to two square foot area, at the edge of suspected damage rather than in the dead center.
- Watch for a few minutes. Irritated caterpillars come to the surface.
Check several spots, especially where the lawn meets a healthy green edge — that boundary is where the front is advancing.
Other signs before you flush
- Birds working the lawn. A flock of birds methodically walking your grass is often the first signal, and pecked holes in the turf come with it.
- Paper wasps hunting low over the grass. They are collecting caterpillars.
- Green frass pellets at the soil line — small green droppings in the thatch.
- A ragged, translucent look to the blades. Young armyworms scrape the leaf surface rather than eating through, giving grass a windowpaned appearance before it browns.
- A visible advancing edge. Damage often moves across a lawn like a front, which is where the name comes from.
Size is everything
Extension is unambiguous: “For effective control, treating armyworms when they are less than 1/2-inch long is key.”
Small caterpillars die easily. Large ones are much harder to kill, and by the time they are large they have already done most of the eating they were going to do. This is why weekly scouting in August beats any product.
One more thing worth knowing before you reach for whatever is under the sink: Extension noted “widespread reports of pyrethroid failures across the country in 2021.” If you have sprayed a pyrethroid and nothing died, that is a documented phenomenon, not your imagination.
Will the lawn recover?
Usually, if it is bermuda and if the growing season has time left.
Fall armyworms eat leaf tissue, not roots or stolons. An established bermuda lawn hit in August generally regrows, especially with adequate water. Extension notes bermuda grows back faster than other turf species.
Recovery is much less certain if the lawn is hit late in the fall, if it was already stressed by drought, or if it is a slower-recovering species like zoysia — Extension repeatedly flags zoysia’s slow recovery from damage.
Support recovery with water and modest nitrogen. Resist the urge to dump fertilizer on a chewed lawn late in the season; heavy late-fall nitrogen on warm-season turf raises the risk of winter injury.
The tracker
Alabama Extension maintains an Alabama Fall Armyworm Tracker, updated weekly with county-level reports. From July onward it is the cheapest early warning available. When neighboring counties start lighting up, start flushing.
Notable years, for perspective
2021 was the benchmark. Alabama Extension entomologist Katelyn Kesheimer said that November: “I have heard from senior entomologists that the state has not seen anything like this since the 1970s, so 2021 is definitely one for the history books.”
2024 brought another outbreak Extension described as massive, driven partly by heat compressing the generation interval.
Neither year was predictable in advance from a homeowner’s back yard. The tracker and a gallon of soapy water were.
Quick reference
- Scout weekly from mid-July to first frost
- Two tablespoons dish soap per gallon, poured over 1 to 2 square feet
- Watch for birds, wasps, green frass, windowpaned blades, an advancing edge
- Treat while caterpillars are under half an inch
- Well-fed bermuda is the preferred target
- Bermuda usually recovers; water it, do not overfeed it late