Sod Webworms in Florida

The larva of the lawn moth, the tropical sod webworm (Herpetogramma phaeopteralis) poses a serious threat to turf grasses in Florida. The larvae feed on grass by shearing the blades off close to the thatch level. They haul the blades underground to consume at their leisure. The resulting damage appears as small, round, dead patches of lawn. If the sod webworm infestation is severe, large, irregular dead patches occur.

The slender-bodied lawn moth holds its whitish-gray-colored wings close to its body. It sports two long, sensory appendages on its head. During the day, the moths reside close to turf grass in shrubs or low trees. They often fly away when disturbed. Once nightfall arrives, the adult lawn moth lays its eggs in the turf grass. In south Florida, the adults begin to breed and produce larvae in June. In the central portion of the state, damage begins in July, and in the northern region of the state the damage is noticeable in August.

Approximately four to six generations of larvae occur per year in South Florida. Each female moth lays seven to 15 eggs on the blades of the grass. The eggs hatch in approximately seven days. The larvae first appear pinkish, cream or white in color. They rapidly grow to approximately 1 inch in length, with coarse hair and black spots. The larvae build silk-lined tubes in the soil and through the roots of the lawn. During the day the larvae remain in their cool, silk-lined tunnels until nightfall, when they emerge to feed on the grass blades.

The larva feeds on the grass nightly for approximately two months. It then returns to its silk-lined tunnel to pupate into an adult moth. Once it emerges as an adult, it lives for only two weeks before dying. In the northern areas of Florida, which often sustain frost, the sod webworm overwinters in its protective, silk-lined tunnel. Adult lawn moths do not eat the turf or pose a danger to other plant life.

Determining how bad the turf is infested with sod webworms will help decide on a course of control. Spraying the lawn with a combination of dish soap and water will force the larvae to the soil's surface. If there are more then five sod webworms per square yard, use insecticides to control them. Sod webworms prefer Bermuda grass best, but they will consume other varieties in Florida (except Bahia grass, which they typically avoid). Reducing the grass's thatch can also help control the sod webworms in the lawn.