Armyworms in the Lawn: How Fast They Spread and Whether the Grass Grows Back

At TurnKey Lawn Care, armyworm treatment is part of the lawn pest work we do across the metro. If a patch of lawn has browned out almost overnight, request a free estimate and we’ll check for caterpillars at the edge of the damage.

This guide covers how to identify armyworms and their damage, why they move so fast, how to confirm them, when treatment works best, and what to expect as the lawn recovers.

How to identify fall armyworms

What armyworm damage looks like

LSU explains that larvae feed on leaf blades and leave behind thin, bare patches of turf. Younger larvae feed on the undersides of leaves and leave them skeletonized, while mature larvae can chew entire leaves. Texas A&M AgriLife describes early damage at the tips of the grass blades, which look transparent where the plant cells have been eaten. It also notes large areas of dead turf next to healthy turf, usually with a sharp, distinct line between them. That sharp line is one of the most useful clues. Drought stress fades gradually from one area to the next, while armyworm damage stops where the caterpillars have reached so far.

Clue	Fall armyworms	Drought stress	Chinch bugs
Speed	Can devastate a lawn in one night	Develops over days of dry weather	Spreads over days to weeks
Edge of damage	Sharp line between damaged and healthy turf	Gradual, uneven fade	Yellow ring around a brown center
Blades	Chewed, skeletonized or eaten to the stem	Folded or wilted but intact	Dry and yellow but intact
Season in Louisiana	Most often June to November	Dry spells, usually summer	Hot, dry mid-to-late summer

Why they move so fast

LSU notes that fall armyworms can complete four or more generations a year in Louisiana. In summer, larvae can mature into adult moths in less than two weeks, though development slows as temperatures cool. That fast turnover means a population can build quickly. A small group of caterpillars in one part of the lawn can become a large, hungry front within days, and each generation lays the eggs for the next. LSU’s seasonal chart shows injury as common from June through October, occasional in April and May, and rare from December through March. For New Orleans lawns, late summer and early fall are when to stay alert.

Which lawns are most at risk

LSU notes that although most turfgrasses are susceptible, Bermuda grass is commonly targeted by fall armyworms. St. Augustine, zoysia and centipede lawns can still be damaged, especially when populations are high. Texas A&M adds that feeding on newly established ryegrass or fescue can stunt the plants or kill them if left untreated. That matters for anyone who overseeds with ryegrass in the fall, since young seedlings have little reserve to recover from. New sod and recently plugged areas deserve extra attention for the same reason. Grass that hasn’t rooted in yet has less to fall back on when caterpillars strip its leaves.

Confirm armyworms before you treat

The soap flush works for armyworms the same way it does for other lawn insects. It brings them up from the base of the grass so you can see and count them.

1. Mix the solution. LSU uses 1 tablespoon of lemon-scented dish soap in 1 gallon of water.
2. Pour at the edge of the damage. The healthy grass right beside the brown area is where active caterpillars are feeding.
3. Watch for five to ten minutes. Caterpillars crawl up and out of the grass as the soap irritates them.
4. Check early or late in the day. Testing in the morning or evening, when LSU says they’re most active, gives the clearest result.
5. Count and note their size. Many small caterpillars means an early, easier-to-control population, while large ones mean feeding is well under way.

Our guide to grub and lawn pest control covers the other quick checks for insect damage in New Orleans lawns.

When and how to treat

LSU recommends treating with insecticide when injury is excessive or when large numbers of larvae turn up during the flush test. Texas A&M adds that applications need to be timed while the caterpillars are small. Texas A&M also gives practical advice around the treatment itself: mow and lightly irrigate before applying the insecticide, and don’t mow for one to two days afterward. That gives the product time to work on the blades where the caterpillars feed. Product choice, rate and any watering-in instructions come from the label, which has to be followed exactly. Because armyworms can do so much damage in so little time, speed matters more than finding the perfect product. We handle armyworm treatment as part of our lawn pest control, and we’ll tell you when a follow-up check makes sense for a second generation.

Will the grass grow back

In most established lawns, yes. Texas A&M notes that damage to Bermuda grass often looks like drought stress but can recover after treatment, and warm-season grasses that still have healthy runners and crowns generally push out new leaves once the caterpillars are gone. LSU points to proper fertilization, irrigation and regular mowing as ways to reduce insect injury and speed turf recovery. Those same steps help a stripped lawn regrow.

• Water deeply in the morning to support new growth, without keeping the lawn constantly wet
• Feed according to a soil test once the lawn is actively regrowing, rather than immediately after damage
• Mow at the correct height for your grass and avoid scalping the recovering area
• Flush-test again a week or two later, since new generations can arrive quickly
• Repair areas that stay bare with plugs or sod once the insects are under control

Our St. Augustine grass care guide and our page on lawn fertilization in New Orleans cover the watering and feeding side of recovery.

Where armyworms come from

The caterpillars you find in the lawn are the larvae of a moth. LSU notes that in summer the larvae can mature into adult moths in less than two weeks, and those moths lay the eggs that become the next wave of caterpillars. That’s why armyworm problems often seem to arrive from nowhere. The moths move in, eggs hatch, and the young caterpillars feed quietly on the undersides of the leaves for a while before the damage becomes obvious. It also explains why neighboring yards often see damage around the same time. If the lawn next door has been stripped, it’s worth running a flush test on yours even if it still looks healthy.

Staying ahead of the next generation

With four or more generations a year, one treatment rarely settles armyworms for the season. A few habits make the next wave easier to catch:

• Walk the lawn early in the morning or after dark every week or so from late summer into fall
• Watch for patches that look chewed at the tips or suddenly thin
• Pay closest attention to Bermuda areas, new sod and any ryegrass overseeding
• Run a flush test at the first sign of damage rather than waiting for a large brown area

Caught early, small caterpillars are easier to control and the lawn has less to recover from. A few minutes of checking each week through the risky months costs far less than resodding a stripped front yard.

Frequently asked questions