Geography
Affected Grass Types
Armyworm
Spodoptera frugiperda (Fall Armyworm)
The fall armyworm is a highly destructive caterpillar stage of a moth species that attacks turfgrass, forage, and many crops. It spreads rapidly, resembles an “army” of caterpillars devouring grass, and can cause serious lawn damage if not managed promptly.
Identification
Armyworm larvae are smooth-bodied caterpillars that vary from green to brown or nearly black depending on age. The most distinctive feature is the pale, inverted “Y” marking on the head capsule, which helps differentiate them from other turf-feeding caterpillars. Mature larvae reach about 1½ inches in length. Adults are gray-brown moths with a wingspan of roughly 1 inch, often showing mottled patterns on the forewings.
Life Cycle
Armyworms go through four stages: egg, larva, pupa, and adult moth. • Eggs are laid in clusters on grass blades, landscape features, or nearby structures. • Newly hatched larvae begin feeding immediately, causing minor “windowpane” damage before growing into larger, more destructive stages. • Once mature, larvae burrow into the soil to pupate. • Adult moths emerge, mate, and begin the cycle again. In warm climates, the entire life cycle may take as little as 30 days, allowing multiple generations each season.
Damage Notes
Early damage begins as light scraping or transparent patches on leaf blades. As larvae grow, feeding becomes more intense, resulting in rapid browning, thinning, and scalped areas of turfgrass. Damage often spreads quickly across the lawn as caterpillars move in groups. Severe infestations can remove most of the green tissue, leaving turf appearing drought-stressed or dead.
Control
Effective control relies on early detection. Small larvae are highly susceptible to treatment, while mature caterpillars are more resilient. Cultural practices such as maintaining proper fertility, mowing height, and irrigation help reduce turf stress. When chemical control is needed, applications should target young larvae and be applied during active feeding periods, typically in early morning or late afternoon. Always follow product labels for rates and turfgrass safety.
Regional Notes
Armyworms cannot survive freezing winters and only overwinter in the southernmost United States. Each summer, adult moths migrate northward, bringing the pest into the Southeast, Midwest, Northeast, and even parts of the Pacific Northwest. Outbreak severity varies year to year depending on weather patterns, storm systems, and migration strength.