Steinernema carpocapsae
Entomopathogenic nematode- Rate
- 250k–500k /m² (≈1 billion per acre at the low end)
- Temp
- 14–34 °C; best 19–31 °C
- Best for
- Lawns; warm, moist soil, applied in the cool of the day
Pest
Fall armyworm
Spodoptera frugiperda
The short answer
The fall armyworm is a moth caterpillar that normally survives the winter in the US only in southern Florida and southern Texas. Every summer the moths fly north on storm fronts, reaching Kentucky in late June or early July and New England from mid-July. Their caterpillars then turn up in late summer and autumn, in lawns and sweet corn. In turf they cross the lawn as a group, leaving a sharp line between brown and green. In corn they chew ragged holes in the whorl and then bore into the ear. The pale inverted Y on the head identifies them.
hero macro · larva showing the inverted Y on the head
A late-instar Spodoptera frugiperda on a grass blade, with the pale inverted Y on the head capsule. Photo: pending.
Identification
Full-grown larvae are about 1–1½ inches (2.5–4 cm) long and green, brown or nearly black, with light stripes down the back and a wide dark stripe along each side. Two marks settle it. The dark head has a pale, upside-down Y on the front. On top of the eighth abdominal segment, near the rear end, four dark spots form a square. Young larvae scrape the leaf surface, leaving translucent window-panes.
The moth has a wingspan of about 1–1½ inches (2.5–4 cm). The male's mottled brown front wings are crossed by a slanting white bar and carry a white spot near the middle. Moths fly on warm, humid evenings. Eggs are laid in masses of 50 to 200, covered with grey scales that make them look furry or mouldy, often on leaves, signposts or buildings. "Armyworm" is also used for other species. In lawns the true armyworm, Mythimna unipuncta, causes similar damage and is managed the same way.
Easily confused with
- True armywormAlso a pestA brown head with dark honeycomb markings, where the fall armyworm has a white upside-down Y on a dark head. In lawns both are managed the same way.
- Corn earwormAlso a pestFeels rough to the touch from tiny spines and has an orange-brown head. Fall armyworm lacks the microspines and has the pale upside-down Y.
- Beet armywormAlso a pestSmaller and dull green with a white stripe along each side and, often, a dark spot on the side above the second pair of true legs. It has no Y on the head and no square of four spots.
Damage symptoms
Fall armyworm hits hardest from midsummer into autumn, after the migrant moths arrive. In lawns the damage builds fast because many larvae hatch from each egg mass and feed together. In corn, late plantings and later-maturing varieties are the ones infested.
- Turf browning in patches that spread, with a sharp line between eaten and green grass
- Damage starting near signposts or buildings and radiating outward
- Newly laid sod hit harder than established lawn
- In corn: small holes and window-pane feeding on leaves emerging from the whorl, then ragged holes
- Sawdust-like frass packed in the corn whorl; holes in the side or tip of the ear
Lifecycle & degree days
A generation takes about 30 days in summer, so numbers can climb quickly once the moths arrive. Each female lays about 1,500 eggs. The caterpillars feed for two to three weeks, drop to the soil to pupate and a new flight of moths follows. The number of generations depends on how far north the moths get and how early: one to two in Kansas, three in South Carolina, four in Louisiana. NC State notes that infestations tend to come earlier after a mild winter.
- Overwinters
- Only in southern Florida and southern Texas; migrates north each summer
- Arrives
- Late June or early July in Kentucky; mid-July into September in New England
- Eggs per female
- About 1,500
- Egg to adult
- About 30 days in summer
- Generations / yr
- 1–2 (Kansas), 3 (South Carolina), 4 (Louisiana)
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Host crops
More than 80 plants have been recorded as hosts, but the fall armyworm prefers grasses: corn, sorghum, Bermudagrass and crabgrass above all. NC State lists Bermudagrass, fescue, ryegrass and bluegrass among the turf grasses it attacks. Among vegetables, sweet corn is the main target.
Monitoring & action thresholds
Action threshold
5 per yd² in lawns; 15% of corn plants
UC IPM treats lawn armyworms and cutworms at 5 larvae per square yard (about 0.6 per ft²) in a soap flush. UMass says control is needed in sweet corn when 15% or more of plants are infested. Kentucky's field-corn threshold is egg masses on 5% of plants, or 25% of plants damaged with live larvae present.
In late summer, check lawns at the edge of any browning patch, early in the morning or late in the evening, when NC State says the larvae are most active. A soap flush brings the caterpillars up: UC IPM mixes 3–4 tablespoons of dish soap in 2 gallons of water, pours it over a square yard and counts for 10 minutes. In sweet corn, UMass scouts 100 plants in groups of 10 or 20 across the patch and looks down into the whorl for larvae and frass.
Beneficial
Biological control
Natural enemies do a lot of work on fall armyworm, but they often lose the race. UF/IFAS notes that a cool, wet spring followed by warm, humid weather in the overwintering areas lets the population escape suppression by natural enemies. Braconid wasps (Cotesia marginiventris and Chelonus texanus) and a tachinid fly parasitise the caterpillars. Ground beetles, earwigs, spined soldier bugs and insidious flower bugs prey on them, and in Georgia predators took 60–90% of pupae. NC State says natural enemies often keep numbers in check. Of the biological products, UF/IFAS says only Bt is currently practical, and it has to be on the leaves when the larvae first appear. The nematode Steinernema carpocapsae suits the lawn phase, where the larvae move through the thatch.
Bacillus thuringiensis kurstaki
Bt (kurstaki)- Rate
- Label rate — ½–4 tsp per gallon on home concentrates; varies by product
- Best for
- Small larvae, on the foliage as they first appear
Cotesia congregata and other Braconidae
Braconid wasps- Kind
- Wild — attract it
- Best for
- Wild parasitoids — spare them
Carabidae
Ground beetles- Kind
- Wild — attract it
- Best for
- Background predation on larvae and pupae
Orius insidiosus
Minute pirate bug- Rate
- 1–2 /m² per release; up to 10 /m² on hot spots
- Temp
- Best above 20 °C; 18–28 °C
- Best for
- Wild predator in corn; not a release target
Cultural controls
Fall armyworm is a migrant, so nothing in the garden stops it arriving. Planting time and a healthy lawn decide how much it costs you.
- Plant sweet corn early, so it is past the whorl stage before the moths arrive in midsummer
- Check new sod closely in late summer; it is more attractive than an established lawn
- Remove thatch, which is daytime cover for the larvae
- Avoid overwatering: armyworms prefer to lay in damp areas with stressed grass
Chemical, last resort
Pyrethroids and carbaryl kill small larvae in turf but also kill the predators and parasitoids that keep later generations down, and they are highly toxic to bees.Check any product before it goes on. Open the compatibility matrix →
Rating: the effect on this pest's natural enemies if a spray hits them or they feed on treated plants. REI is the re-entry interval on farm and greenhouse labels; home labels usually give none, so follow the label.
Sources
UF/IFAS EDIS EENY-098, Fall Armyworm, Spodoptera frugiperda (Capinera)
Univ. of Kentucky ENTFACT-110, Fall Armyworm in Corn (Bessin, rev. 1/26)
NC State TurfFiles, Fall Armyworms in Turf (Billeisen & Brandenburg, 2017)
UMass Extension Vegetable Program, Fall Armyworm (sweet corn fact sheet)
UC IPM Pest Management Guidelines: Turfgrass — Cutworms and Armyworms (Sutherland et al., 09/09)
UC IPM Pest Notes 7476, Lawn Insects (Sutherland, Dreistadt & Harivandi, 09/2014)
Purdue Extension E-61-W, Turfgrass Insects (Gibb & Richmond)
DiPel DF label, EPA Reg. 73049-39 (2022)
UC IPM, Relative Toxicities of Insecticides to Natural Enemies and Honey Bees (tomato, 09/16)
Page status
Drafted from the sources below, then checked claim by claim against those sources on 23 September 2026.
Suggest a correction →Fall armyworm by crop
The same pest behaves differently on different hosts. Each page below gives the host-specific control, rate and threshold.