Chinch Bugs, Sod Webworms, and Armyworms: The Three Summer Pests That Quietly Damage Lawns

Lawn Squad • June 2026

Short Answer: Chinch bugs are tiny black-and-white insects that suck juices from grass crowns, creating expanding yellow-then-brown patches in St. Augustine, Bermuda, and Zoysia. Sod webworms are caterpillars that hide in thatch by day and chew grass blades at night, leaving small ragged patches with green pellet droppings and silken tunnels in the thatch. Armyworms are larger striped caterpillars that march across a lawn in groups and can clear-cut a yard in 48 hours. Early identification with the float test (chinch bugs), the soap drench (webworms and armyworms), or a flashlight walk after dark turns a treatable spot into a saved lawn.

It is a Thursday afternoon in late June. A homeowner walks the back fence line and stops at a patch of grass near the southern exposure that looks off. It is yellow, almost the color of straw, in an irregular shape about the size of a beach towel. Last weekend it was not there, or at least it was not this obvious. The sprinklers are working. The same fertilizer schedule has been in place for two years. Something is eating the lawn, and it is not stress.

This is the conversation we have constantly from June through September across the country. Three summer pests that live in the grass itself, not in the soil like grubs, cause more lawn damage than most homeowners realize. They are easy to miss because they are small, nocturnal, or hidden in the thatch. By the time damage is visible from the porch, the population has been working for one to three weeks. Here is how to find them before they find more lawn.

Chinch Bugs: The Yellow Patch That Spreads

Chinch bugs are tiny, about the size of the period at the end of this sentence in their younger stages, and a sixth of an inch as adults. Adult chinch bugs are black with white X-shaped markings on the wings. The nymphs are reddish to orange with a white stripe across the back, and they are the stage that does the most feeding.

They feed by piercing grass crowns with a needle-like mouthpart and injecting a toxin that prevents the grass from moving water and nutrients. The grass yellows in expanding patches, then turns straw-brown and dies. Damage usually starts in the hottest, driest, sunniest part of the lawn, often along sidewalks, driveways, or southern exposures where heat reflects from concrete.

Chinch bugs are the dominant warm-season turf pest in St. Augustine, Bermuda, and Zoysia lawns across the South and Gulf Coast. Hairy chinch bug affects cool-season lawns (Kentucky bluegrass, fescue, ryegrass) across the Northeast, Midwest, and Mid-Atlantic. Both feed the same way.

The defining test: the float test. Cut both ends off a coffee can or large soup can, push it two inches into the soil at the edge of a yellowing patch, and fill it with water. Watch for ten to fifteen minutes. Chinch bugs float to the top in numbers. Five or more in a single can means treatment is warranted. Twenty or more means the population is established.

Damage signal: irregular yellow-then-brown patches that expand outward over days or weeks, in hot dry sunny spots. The damage does not respond to extra water, which is the difference between chinch bug damage and drought.

Sod Webworms: The Damage You See in the Morning

Sod webworms are the larval stage of small tan to grayish moths you may have seen flitting low across the lawn at dusk. The moths themselves do not damage grass. The larvae do.

The caterpillars are about an inch long when fully grown, with a brown head and a gray-green body marked with darker spots. They are nocturnal feeders. By day, they hide in silken tunnels they construct in the thatch layer at the base of the grass. By night, they emerge and chew grass blades close to the soil, leaving ragged short stubs.

Damage appears as small irregular patches an inch to a few inches across with notched and shredded grass blades. Tiny green pellets (the caterpillars' droppings) sit in the thatch around the damaged grass. As the population grows, the small patches join into larger irregular areas of thinned, scalped-looking lawn.

Sod webworms affect almost every turfgrass species, with the worst damage typically in stressed lawns, especially newer sod and lawns with dense thatch. They peak in mid to late summer, with multiple generations in the South.

The defining test: the soap flush. Mix two tablespoons of dish soap into two gallons of water, pour evenly over a four-foot-square area of suspect lawn, and watch for two to five minutes. The soap irritates webworms and they crawl to the surface. Five to ten caterpillars per square yard is a treatment threshold. Twenty is a major infestation.

Damage signal: small ragged patches of chewed grass that appeared overnight, green pellet droppings, fine silken tunnels visible if you part the grass at the soil line.

Armyworms: The 48-Hour Lawn Disaster

Armyworms are the dramatic one. Fall armyworm (Spodoptera frugiperda) is the species responsible for the vast majority of armyworm damage to lawns. It is a striped caterpillar, an inch to an inch and a half long when fully grown, with a brown to green body marked with yellow or white stripes along the back and sides. The face has a distinct inverted Y-shaped marking, which is how entomologists confirm the species.

The name comes from the behavior. Armyworms move across a lawn in large groups, feeding on grass blades as they go. A heavy population can scalp a lawn from green to brown in 24 to 48 hours, leaving a sharp edge where they have been versus where they have not yet reached.

Adult moths fly long distances on storm fronts and lay egg masses on light-colored surfaces near lawns, including the underside of patio furniture, mailboxes, and white fences. Eggs hatch in three to five days. Young larvae feed lightly, then molt and feed harder as they grow. By the time damage is visible, the population has been there for one to two weeks and is reaching peak feeding.

Armyworms are most damaging across the South, Southeast, and southern Plains, and increasingly the Mid-Atlantic and lower Midwest as fall outbreaks move north. Late summer and early fall are the worst windows, but spring and early summer outbreaks happen in the Deep South.

The defining test: walk the lawn at dawn or after a heavy dew with a flashlight after sunset. Armyworms are most visible at those times, climbing on grass blades to feed. A soap flush also brings them up quickly. If you see five or more per square yard, treat the same day, because a heavy population can clear-cut a lawn before the weekend.

Damage signal: a sharp line between scalped grass and intact grass, advancing across the lawn over a few days. Visible caterpillars at dawn, dusk, or after rain. Brown stripes on the grass blades from feeding marks. Birds (especially starlings) suddenly working a yard hard.

What All Three Have in Common

These three pests live in the grass and thatch, not the soil. Grub treatments do not control them. Watering more does not help. The damage pattern looks like drought or heat stress at first glance and gets misdiagnosed constantly.

All three respond to the same general categories of insecticide if caught early. Pyrethroid products (bifenthrin, lambda-cyhalothrin, cyfluthrin) work on chinch bugs, webworms, and armyworms. Carbaryl is effective against webworms and armyworms. Selective products like chlorantraniliprole (Acelepryn) have residual activity against caterpillars and are softer on pollinators.

What changes by species is timing and application. Chinch bugs require a treatment that reaches down into the crown of the grass, not just the surface, which means watering in moderately after application. Webworms need a surface treatment that contacts the caterpillars during their nighttime feeding. Armyworms can be treated in the cool of early morning when the caterpillars are exposed.

Why Misdiagnosis Costs So Much

The patterns these three pests create are easy to mistake for other things. Chinch bug yellowing is often blamed on drought, and the homeowner increases watering, which does not help and may actually worsen the stress. Sod webworm damage is often blamed on dog urine or scalping from the mower. Armyworm damage moves so fast it is sometimes blamed on a sudden disease.

The cost is one to three weeks of lost treatment time. In that window, a chinch bug patch can become a quarter of the yard, and an armyworm population can level the lawn. The float test, the soap flush, and a flashlight walk are all free. They turn a guess into a diagnosis.

The customers across our markets who lose the least lawn to these pests are usually the ones who know the tests and use them at the first sign of unexplained yellowing or ragged patches. Either that, or they are on a service program with a tech who runs them on every visit.

Prevention and Cultural Defense

Some cultural conditions favor these pests, and changes to those conditions reduce pressure.

What to Do Next

If you see unexplained yellow patches, ragged chewed grass, or a fast-advancing brown line in the lawn, the diagnostic tests are free and take ten minutes. If the tests turn up insects, get the right product on the right way within the same week.

Lawn Squad has local teams across the warm-season South, the cool-season North, and the transition zone, each trained to diagnose and treat the chinch bug, webworm, and armyworm pressure that matters in their specific region. Find your nearest Lawn Squad at lawnsquad.com or call 833-816-7508 to be connected with the local team.

Our VitaminLawn program includes regular scouting on every visit, which is how we catch surface insect populations weeks before damage shows up from the porch. One careful walkthrough catches what a quick mow-and-go skips, and that is usually the difference between a treated patch and a renovation.