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Identify and Treat Armyworms and Sod Webworms

Recent hot, dry weather may bring an invasion of pests to our lawns earlier than usual. Fall armyworms and sod webworms, both voracious caterpillars, can munch their way across your lawn, leaving destruction in their wake. Arm yourself with information to identify and annihilate the threat, so your lawn stays healthy and beautiful.

Fall Armyworms

As their name suggests, fall armyworms usually begin their rampage in early fall, but they may show up as early as July or August, feeding on our lush grassy lawns. Because the striped caterpillars appear in such large numbers, they can cause major damage in short order.

A pest for more than a century in the Southeast, the adult moths migrate each spring from Florida, where they overwinter in the mild climate. Each moth lays a few dozen to a few hundred eggs along the way as they move northward, building populations exponentially throughout the summer months. They reach most areas of Georgia by early fall and continue to reproduce—and eat our grass—until the first frost.

Damage

Armyworms harm virtually all turf grasses by chewing the plant tissue and creating ugly web patterns in the leaves. The armyworm larvae strip foliage in one area of the lawn and move, usually all together, to the next source of food. Moving en masse like an army earned these destructive critters their military designation.

Damage varies in severity depending on the type of grass and the overall health of the grass prior to the infestation. Armyworm damage rarely kills a lawn on its own, but it can significantly weaken your grass, making it far more susceptible to failure from drought and disease.

Win the War

Watch for birds clustered in a particular area of your lawn, often an early indication your yard has been invaded by armyworms. The caterpillars are dark in color with several light stripes down the length of the body and an inverted “Y” at the head. Young armyworms measure ½ to ¾ inch long, reaching 1-1/2 inches before burrowing into the soil for the pupa stage. They emerge two weeks later as adult moths, laying eggs to begin the cycle again.

If the worst happens and armyworms do march into your lawn and flowerbeds, treating with insecticide is your best defense. The University of Georgia extension office recommends Bt insecticides, which are nontoxic to humans and eradicate caterpillars without harming beneficial insects in your yard. Several brands are readily available at home and garden centers.

Sod Webworms

Another dastardly caterpillar that feeds on Georgia lawns this time of year is the sod webworm. The adults appear as small gray or brown moths, which scatter eggs as they fly around the yard. Once hatched, the caterpillars chew on the tender grass blades, creating notched, ragged edges. Sod webworms prefer newly established lawns, and they attack many grass varieties, including Bermuda, Zoysia, Centipede, and St. Augustine.   

A major infestation can wipe out a lawn in a matter of days, so if you notice irregular brown patches in your otherwise green yard, try a soap flush in the affected area to confirm. Add two or three tablespoons of liquid dish soap to a gallon of water and spread with a watering can over a small 3-foot by 3-foot section in the affected area. If webworms are present, the soap solution will force the caterpillars to the surface of the lawn.

Look for caterpillars up to ¾ inch, covered in fine hairs with a dark head. Their bodies vary in color from light pink or green to a yellow brown. Treat the infested areas with Bt insecticide in the early evening, when the caterpillars begin to feed.

If you have additional questions about pest infestations or unidentified damage to your grass, give our Certified Turfgrass Professionals a call at 770.832.8608 or email at info@NGTurf.com.