Watch for sod webworms in lawn during late summer & fall

Q. I noticed small light 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. The moths have a wingspan of ¾ to 1 inch and are tan to gray. The moths do not cause damage.

Q. I noticed small light 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. The moths have a wingspan of ¾ to 1 inch and are tan to gray. The 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. The larvae are small caterpillars. They’re greenish when young, turning brown at maturity. Their feeding results in notched or ragged leaf edges.

Sod webworms feed 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 have been chewed away.

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. The soap irritates the caterpillars causing them to crawl to the surface to be more easily seen.

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 may also use insecticides that contain Bacillus thuringiensis, a bacterium that only kills caterpillars and won’t harm beneficial insects in your lawn.

Sod webworms weaken the lawn 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.

The September plant clinic will be held Friday, September 13 from 9 a.m. to noon at the Okaloosa County Extension Annex, 127 NW Hollywood Blvd in Fort Walton Beach.

The plant clinic provides a place and time for people to bring in samples of plants for diagnosis including weeds for identification.

Bring a fresh sample of the weed, plant, insect, etc., that you’d like diagnosed to the clinic. This may include a plant stem with several leaves, a 4-inch square of grass with roots attached, etc.

Larry Williams is the Extension horticulture agent with the Okaloosa County Cooperative Extension Service, University of Florida. Contact Larry at 689-5850 or email lwilliams@myokaloosa.com.