Armyworms are caterpillars that eat turfgrasses. They attack in large numbers, like an army, and can destroy a lawn in a matter of days. Luckily, armyworm damage is fairly rare, but every now and then, seemingly out of the blue, an invasion can occur and it needs to be recognized quickly.
There are two types of armyworms, the true armyworm and the fall armyworm. Both are a major hazard to crops, and they will move from field to field as their food supply is exhausted. The same thing happens when they invade a neighborhood, although it is usually the fall armyworm (Spodoptera frugipeda) that causes lawn damage. Armyworms overwinter in the south, but the moths migrate north and lay their eggs. Where they actually end up laying their eggs can be different each year. Oklahoma had a serious problem with armyworms invading residential lawns in mid to late summer of 2000. As far as we know, there hasn’t been a problem since (and there hadn’t been a problem for 10 or 15 years prior.)
Damage may at first appear as heat stress—brown patches in the lawn. You can actually see ragged edges on the grass where the armyworms have been feeding. With high populations, these caterpillars can eat the grass to the ground, leaving large bare areas.
Fall armyworm larvae are hairless and vary from light tan to black, with three light yellowish stripes down the back. They are easily identified by the white inverted “Y” mark on the front of the dark head. Unlike true armyworms, fall armyworms have teeth.
If you notice any activity or armyworm caterpillars, call us immediately for an application of insecticide. In rare cases (such as in 2000 in Oklahoma,) armyworms can destroy a lawn in 24 hours.