Largely found in the South, especially on bermudagrass, armyworms can infest lawns and cause severe damage. The first sign of trouble is small patches of brown grass with the edges of the blades chewed. Some blades may be completely eaten.
Armyworms are the larvae of a moth. The caterpillars are light green or tan in their early growth stage and dark green or brown in later stages. Full-grown larvae are 1-½ to 2 inches long and almost hairless. They can be identified by a series of green, yellow, or brown stripes down the length of their bodies. They primarily eat grass blades, but will also eat some vegetables, like beans, cabbage, corn, onion, pepper, pea, and radish. Large infestations can completely defoliate a lawn in a few days.
Watch for Moths and Damage
Armyworms generally don't survive freezing temperatures, but adult armyworm moths sometimes ride storm fronts into the North. The adults are tan or brown moths less than an inch long, with a white spot in the middle of each forewing. The egg-laying females prefer to attach masses of eggs on tree leaves. As the larvae move into a lawn, their damage usually becomes apparent starting close to the edges. As they feed, the larvae leave brown patches in the lawn. The grass blades are ragged where they were fed on, and in large infestations the blades may be sheared to the ground.
Treat Early for Best Control
Armyworms are surface feeders and are easily controlled by insecticides when identified early enough. Apply Ortho® Bug B Gon® Insect Killer for Lawns when you find 4 to 5 small, healthy armyworms per square foot of lawn. Under small to moderate infestations, although the grass blades may be chewed, the crowns are not damaged by the feeding and can recover if the damaged area is kept well fed and watered. The most severe damage occurs when armyworms attack during hot, dry weather.