Young caterpillars, or larvae, injure turfgrass by chewing notches along the edge of the leaves. This creates a ragged appearance that may be hard to notice at first. Mature caterpillars eat a lot before they pupate and consume patches of turfgrass down to the crown. Because the turf looks scalped so quickly, people think that the damage occurs “overnight.” Several caterpillar species can be turfgrass pests, including the tropical sod webworm, the fall armyworm, and the striped grass looper.
IdentificationTropical sod webworm larvae are gray-green, have brown spots on each segment, and are the smallest of the three species. Mature larvae can be 3/4 to 1 inch in length, and they pupate in the thatch or on the soil surface. Fall armyworm larvae can be green or brown, and mature larvae are 1½ inches long with four pairs of prolegs (fleshy legs on abdomen). As larvae grow, light stripes appear along the length of the body and dark spots appear on the top of each segment. Fall armyworm larvae have an inverted light-colored Y on the front of their heads. They pupate in the soil. Striped grass looper larvae have longer and thinner bodies and “loop” like inchworms when crawling. They only have two pairs of prolegs. Their color ranges from cream to black, there is a light-colored narrow stripe down their backs, and many stripes on their heads. Striped grass loopers pupate on tall pieces of grass or small shrubs,
Biology and Monitoring
Tropical sod webworm is most active from April through November in north Florida, but may occur year-round in south Florida. Three to four generations occur in Florida each year. Tropical sod webworm larvae feed on St. Augustinegrass, bermudagrass and zoysiagrass. Fall armyworm occurs year-round in south Florida and migrates northward each spring. This means that populations can be damaging in the spring in south Florida, but don't build up until fall in north Florida. Fall armyworm will feed on all turfgrasses, but prefers bermudagrass. Striped grass looper also occurs year-round in south Florida, and isn't a problem until fall in north Florida. Striped grass looper is primarily a pest on bahiagrass in pastures, but will readily infest other turfgrasses. Larvae of these species are active at night and will hide in a curled position near the soil surface during the day. Fall armyworm larvae may also feed during the early and later parts of the day. Green or brown pellets of frass may be visible on the soil surface, indicating that larger larvae are present. One generation of tropical sod webworm is about 6 weeks; fall armyworm and striped grass looper can develop in about 4 weeks under warm weather conditions.
To find larvae, part the grass in suspect areas and look for chewed leaves, silken webs, green or brown frass, and larvae. Use soap flushes (2 TBSP liquid dishwashing soap mixed in 2 gallons of water) to drench larvae or other potential pests out of the ground. Pour the mixture on 1 square yard of damaged grass, and observe after 5 minutes. If nothing emerges, examine several other areas.
The adults (moths) of all three species are active from dusk till just after dawn. A commercially available sex pheromone lure can be used to monitor fall armyworm. The sex pheromone for striped grass looper is known but not available. Researchers are currently determining the sex pheromone for tropical sod webworm.