During the past few weeks, numerous people have contacted the Okaloosa County Extension Office seeking diagnostic assistance and control options concerning fall sod webworms in their lawns.
Sod webworms are not consistently a problem every year. Some years their numbers are low enough that they are not a problem. Some years we do not see them at all. Those years when they are a problem, it’s usually not until late summer and early fall that they become active. And, they may continue to feed on lawns until frost occurs. Sod webworm larvae are commonly found feeding on St. Augustinegrass, bermudagrass, and zoysiagrass.
Fall armyworms and sod webworms can attack at the same time. Sod webworms are the smaller of the two species, reaching a length of about 3/4-inch. Armyworms grow to 1/2-inch in length. Both of these caterpillars are greenish when young, turning brown at maturity.
Armyworms generally have a light mid-stripe along their back with darker bands on either side of the mid-stripe. Their feeding is similar, resulting in notched or ragged leaf edges.
Sod webworms tend to feed in patches while armyworms cause more scattered damage. Sod webworms feed at night while armyworms will be seen feeding during the day. The adults of both species are fairly small grayish to brown moths.
Because sod webworms feed at night, don’t be surprised if you can’t find them during the day. The greenish or tan caterpillars will be resting, curled up near the soil line.
If you have damaged spots in your lawn, look closely for notched leaf blades, the telltale signs of their chewing damage. They may also be found by parting the grass and looking for small green caterpillars (no larger than 3/4-inch in length) curled up on the soil surface and for small green or brown pellet-like droppings.
Fall armyworms and sod webworms can be controlled with the same insecticides as the other lawn insects. But you may also use insecticides that contain Bacillus thuringiensis (Bt), a bacterium that kills only caterpillars and won’t harm the beneficial insects in your lawn. control should be directed against only the caterpillars, not the non-feeding, flying adult moths. Always follow the label directions and precautions for any pesticide you use.
For more information on lawn caterpillars contact the UF/IFAS Extension Office in your County or visit http://edis.ifas.ufl.edu/topic_tropical_sod_webworm.