Fall Armyworms in Tennessee: How to Spot Them and Protect Your Lawn

On Monday the lawn looked fine. By Thursday there's a brown patch the size of a parking space, and it's bigger every morning. A flock of birds is working the yard like it's a buffet. If it's late summer or early fall in Middle Tennessee, there's a good chance you're looking at fall armyworms. Here's how to confirm it, how worried to be, and what to do next.

What Fall Armyworms Are

Fall armyworms are caterpillars, the young stage of a night-flying moth. They don't survive our winters. Each year the moths work their way north from the Gulf states, and by late summer their numbers have built up enough to reach Tennessee. The moths lay eggs in fuzzy masses on fences, siding, mailboxes, and grass blades, and the caterpillars that hatch start eating right away.

Young ones are small, pale green, and easy to miss. Full-grown ones are about an inch and a half long, green to brown to nearly black, with stripes down the sides and a light-colored upside-down Y on the head.

They get the name because they move like an army: they chew through one lawn and march on to the next. That's why a whole street can get hit in the same week.

Why late summer and fall

In Middle Tennessee, armyworm activity usually runs from late July or August into October, and several generations can come through in one season. Some years are quiet. Others bring outbreaks that hit whole neighborhoods at once. The timing is especially rough because it lines up exactly with fescue seeding season.

How to Spot Armyworms Early

• Brown patches that spread fast. Damage that grows noticeably from one day to the next. Drought stress doesn't move that quickly.
• Chewed, ragged grass. Early feeding scrapes the leaf surface and leaves blades looking thin and see-through. Later, the grass gets chewed down to stubble.
• Birds. A lot of birds pecking at one area of the lawn is one of the best early warnings you'll get.
• Moths and egg masses. Grayish, fuzzy clusters on siding or fence posts, or small moths fluttering up when you walk the lawn at dusk.
• Time of day. Caterpillars feed most in early morning and evening, and hide down near the soil in the heat of the day, so a midday glance can miss them.

The soap flush test

This is the easiest way to know for sure. Mix a couple of tablespoons of dish soap into a gallon of water. Pour it slowly over about a square foot of grass at the edge of the damage, where brown meets green, not in the dead center. Wait a few minutes. The soap irritates the caterpillars and they wriggle up to the surface. If several come up, you have your answer. Try a few spots around the yard to see how widespread they are.

Bermuda Usually Bounces Back. Fescue Might Not.

How worried you should be depends on your grass.

Bermuda and zoysia spread by runners and keep their growing points close to or below the soil surface. Armyworms strip the leaves, but in most cases the plants survive, especially when there are still warm weeks ahead. A Bermuda lawn that looks scalped in September will usually green back up within a few weeks. Damage late in the season may not fully recover until the lawn comes out of dormancy in spring.

Tall fescue is a different story. It doesn't spread by runners, so plants chewed down to the crown can die. The biggest risk is new fescue seedlings. A fresh stand of tender grass can be wiped out in a few days, so if you just seeded, walk the lawn every day or two through early fall.

What to Do If You Find Them

• Confirm first. Use the soap flush. Brown patches can also come from drought or disease, and treating for the wrong problem wastes time. Our guide to dollar spot, armyworms, and other turf problems helps you tell them apart.
• Act quickly. A heavy infestation can do a lot of damage in a few days. If you're finding several caterpillars per square foot, it's time to treat.
• Treat beyond the brown. The caterpillars are at the edge of the damage and in the green grass next to it, moving forward. Treating only the dead area misses them.
• Help the lawn recover. Once they're under control, water deeply during dry spells so Bermuda can push out new growth.
• Reseed fescue where needed. If fescue patches haven't greened up in a couple of weeks, they're likely gone. There's often still time to reseed in October through aeration and overseeding.
• Keep watching. A second wave a few weeks later is common, so don't assume one round means you're done for the year.

Prevention Beats Cleanup

You can't stop moths from flying in, but you can be ready when they do. Our Essential program includes army-worm protection along with disease prevention and three fungicide applications. That makes it a good fit for Bermuda lawns that have been hit before and fescue lawns being seeded in the fall, when a new stand is most at risk.

If brown patches are spreading and you're not sure why, we'll take a look and tell you what's going on. Get your free estimate. No contracts, no surprises.

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