Tropical Sod Webworm and Lawn Care

Tropical sod webworm larvae are destructive pests of warm season turfgrasses in the southeastern U.S., especially on newly established sod, lawns, athletic fields, and golf courses. Larval feeding damage reduces turfgrass aesthetics, vigor, photosynthesis and density. The first sign of damage is often caused by differences in grass height in areas where larvae are feeding. Tropical sod webworms are part of a pest complex of warm season turf caterpillars in Florida that include fall armyworm (Spodoptera frugiperda), striped grass loopers (Mocis spp.), and the fiery skipper (Hylephila phyleus).

The moths are dingy brown, and their wing spread is about 20 mm (3/4 inch). At rest, wings are held in a triangular shape. Adult males usually have six abdominal segments, whereas females have five. The terminal segment in males has a slim extension, while the anal segment of the female has a large fusiform opening.

Adult females deposit clusters of 10 to 35 creamy-white eggs on the upper surface of grass blades. The eggs become brownish-red as they mature. The eggs are flattened, overlapping, and slightly oval in shape. Eggs average 0.7 mm (length), 0.5 mm (width), and 0.1 mm (height).

Larvae are the damaging stages. Neonates (first instar larvae) are small (1 mm long) and their feeding activity is hardly noticeable. The first four larval stages (instars) are ‘window feeders’, i.e., they only feed on the upper surface of grass blades, and so the injury they cause is often overlooked. Fifth and sixth instars can severely damage grass by chewing entire sections off the leaf blade. Larval feeding occurs at night, and larvae hide in the thatch during the day. Caterpillars prefer dry and hot grass areas. Early damage is hard to notice and creates a ragged appearance, but as larvae grow, they consume considerable quantities of grass before pupating. Grass may recover if infestations are not too severe, but feeding damage causes yellowish and brown patches and often leads to the ingress of weeds.

Despite the economic importance of Herpetogramma phaeopteralis, little information on integrated pest management programs of this pest has been reported. Several insecticides may be used to control this pest, but appropriate timing, risks of resistance, and non-target impacts need to be considered. Finding larvae with soap flushes, especially if moths were previously seen, and spot treatment of infested areas are recommended. The sex pheromone of this species, which would allow sex-based monitoring, has not been described.

Photo Credit: James Kerrigan, University of Florida