Army Worms - Insecticides

Fall armyworms are the caterpillar stage of a nondescript, small gray moth which overwinters in Florida and the tropics. Florida-grown sod which was recently laid might have had eggs on it and now the eggs have become “worms”.

Your first sign of a fall armyworm infestation might be several birds clustered on a turf area. Although birds eat the caterpillars, they are no match for hundreds of them in one lawn. Closer examination of the grass reveals several (perhaps dozens) of caterpillars munching on turf blades. Young worms are ½ to 3/4 inch long. Matures ones are 1 ½ inches long. They are dark colored and have several light stripes down the length of the body. The head or “face” has an inverted “Y”on it.

Fall armyworms rarely kill grass but some lawns may be severely weakened. If you suspect fall armyworms but can not find the caterpillars on the grass, use a soap flush to bring them to the surface. Feeding damage, coupled with damage from the recent drought, may justify applying insecticides. Experts say 5 or more caterpillars per square foot in turf might be a reasonable treatment threshold.

Carbaryl (Sevin), deltamethrin, and other insecticides are effective caterpillar killers. Products containing B.t. are effective only on small (1/2 inch or less) worms. Irrigate before treating, to move the caterpillars out of the thatch. Treat in late afternoon, when the caterpillars are likely to begin feeding. If possible, mow before you treat and then do not mow for 3 days after treatment. Fall armyworms can not overwinter in north Georgia.