During the past few weeks people have contacted the Okaloosa County Extension Office seeking diagnostic assistance and control options concerning fall armyworms and sod webworms in turf grass. This includes farmers with these critters in their pastures ahd homeowners whose lawns are being eaten away by these hungry caterpillars. We’ve even had requests from a local landfill and from a local airport with grass runways.
Sod webworms and fall armyworms are not a problem every year. 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 might continue to feed on lawns until frost occurs.
Fall armyworms prefer Bermuda grass but will feed on any lawn grass. Sod webworm larvae are found feeding on St. Augustine grass, Bermuda grass and zoysia grass.
Armyworms and sod webworms can attack at the same time. Webworms are the smaller of the two species, reaching a lengths of about 3/4 inch. Armyworms grow to 1 1/2 inches 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. Webworms tend to feed in patches while armyworms cause more scattered damage in turf areas. Webworms feed at night while armyworms will be seen feeding during the day. Adults of both species are fairly small grayish to brown moths.
If you have damaged spots in your lawn, look closely for notched leaf blades, the telltale signs of their chewing. They might be found by parting the grass and looking for small green caterpillars (no larger than 3/4 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 might also use insecticides that contain Bacillus thuringiensis, a bacterium that only kills caterpillars and won’t harm the beneficial insects in your lawn. Control should be directed against the caterpillars, not the non-feeding, flying adults. Always follow the label directions and precautions for any pesticide you use.
Additional information on thse caterpillars is found at http://edis.ifas.ufl.edu/IN608 .