Tropical Sod Webworms Active in Local Lawns

by Larry Williams

Q. I noticed small brown moths flying low to the ground in my lawn. Should I be concerned about this?

A. Yes and no. These are probably adults of the tropical sod webworm. Moths have a wingspan of about ¾ inch and are a dingy brown. Moths do not cause damage. So don’t bother trying to control them. But their presence is reason to keep a close eye on your lawn for evidence of the larval stage feeding. Larvae are small caterpillars. They’re greenish when young, turning brown at maturity. Their feeding results in notched or ragged leaf edges.

Tropical sod webworms normally do not survive our north Florida winters. They eventually reach our area of the state in late summer to fall. Some years their population will be high. Other years we do not see them.

Sod webworms have been active in many local lawns this summer.

Tropical_sod_webworm02Sod webworms feed mostly at night. They rest, curled up near the soil line during the day. If your lawn has damaged spots, look closely for notched leaf blades from their chewing. You may first notice a patch in your lawn that looks like it has been mowed extra low. Closer inspection reveals grass blades that are chewed away. Caterpillar feeding on zoysiagrass shows up more as translucent whitish tan areas on the surface of individual blades more so than notched blades.

Sod webworms will feed on all of our warm season turf grasses.

Soap flush is a technique to survey for some lawn insects, including sod webworms. Mix two ounces of liquid dishwashing soap in two gallons of water and apply with a sprinkling can to a four square foot area of injured turf. This technique is a good way to identify sod webworms.

They may also be found by parting the grass and looking for small green caterpillars curled up on the soil surface and for small green pellet-like droppings. Because they are nocturnal, a flashlight used at night will expose the caterpillars feeding.

Sod webworms can be controlled with the same insecticides as the other lawn insects. But you also may use insecticides that contain Bacillus thuringiensis, a bacterium that only kills caterpillars. Caterpillars tend to be more of a problem in lawn fertilized heavily in late summer. Always follow the label directions and precautions when using any insecticide.

Sod webworms may weaken lawns but usually do not kill the grass. Because damage occurs late in the growing season, the lawn may not completely recover until spring.

Additional information on these caterpillars is found at http://edis.ifas.ufl.edu/in968.

Larry Williams, UF/IFAS Extension Agent, Okaloosa County, August 18, 2016
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