Of the thousands of moth species that occur in North America, only a handful are pests of turfgrass such as armyworms, cutworms, and sod webworms. The immature “worm” or caterpillar growth stages are what damage turf by chewing the leaf blades. In lawns of southern states, tropical sod webworms are probably the most commonly seen. While severe infestations of webworms can completely strip a turf of its leaves, in most cases the turf will regrow them from runners once the caterpillars are gone. As with any type of pest, a good management approach depends on correct diagnosis of the issue and timing control applications properly based on the growth cycle.
Sod webworms can occur almost anytime it is warm but are most prominent from mid-summer through fall. Adult moths are typically light brown and fairly nondescript with a wing span of ½ to ¾ inches. This could describe many dozens of native moth species, which may simply be seeking shade in a turf area or were attracted to lights the night prior. The mere presence of moths in a turf area should not cause alarm. Sod webworm moths are actually nectar feeders and do not directly damage the turf. They do however lay eggs on turf leaf blades, which can develop into caterpillars. Even so, low numbers of caterpillars may go unnoticed and not require treatment, so it is important to recognize damage and confirm that caterpillars are present before deciding to treat.
The first sign of webworm damage will be holes and irregular notches on the edges of the leaf blades. In zoysiagrass the leaves will turn brown and appear skeletonized as they are tougher for the caterpillars to chew. If damage accumulates the affected area will appear shorter than the surrounding turf and may look as if someone scalped it with a weed-whacker. The caterpillars feed at night and usually spend the day coiled up in the thatch layer to avoid the heat and predators, so seeing them in person requires some closer inspection of the thatch. The caterpillars are brown to green with a few spots and grow up to about an inch in length. Mixing 1 tbs. of lemon-scented dish soap in a gallon of water and spreading it over a 3 foot diameter area will drive them upward if present.
If caterpillar damage becomes unacceptable, Martins® has several products to control them. Cyonara® Lawn & Garden Insect Control is a concentrate that you dilute in water and spray on your lawn. Calculate the area (square footage) of the lawn to be treated by multiplying the length by the width. Then follow the mixing directions in the table for “Lawns” on the label.
Cyonara L & G Ready-to Spray is a ready-to-use version of Cyonara L & G Insect Control. It’s packaged in a hose-end sprayer, so no measuring and mixing is needed. After shaking the product well, connect the Ready-to-Spray nozzle to a hose and follow the application directions on the label. One quart of Cyonara L & G Ready-to Spray will cover 16,000 square feet (slightly more than ⅓ of an acre).
For best webworm control using any of these products, completely wet the grass a few hours before applying the product, and don’t water or mow the grass for 24 hours after treatment.
Ian Rodriguez Technical Service Manager Quali-Pro