Justin Turner doesn’t plan on a fight with fall armyworms in soybeans every year. But he knows he’d better be ready to rumble if they invade.

Turner farms in northeast Louisiana at MerRouge. His soybean and corn rotation can face excessive insect infestations if control measures aren’t taken in the warm, humid and wet climate that often sees heavy fall rains. And if fall armyworms (FAW) strike, they’d better be controlled before they can chomp away at leaves and eventually defoliate a field.

FAW, as well as common armyworms and the southern armyworm variety, have sporadic cycles on the region’s crops. FAW can be absent for two or three years, then sneak up on growers in a flash.

“They’re pretty easy to control,” says Turner, who’s a regional crop consultant when he’s not farming. “But if it’s too wet to spray, they can get away from you.”

FAW were actually bad in 2010 due to dry weather. They prefer foliage, but with the dry summer, they “moved from grassy road ditches and thickets out into lush irrigated soybean and rice fields,” says Turner.

FAW look similar to corn earworms and are the larvae of small, night-flying moths, university entomologists point out that. The larva has a prominent white inverted Y-shape on its head. They generally eat foliage and are easily seen. They are ferocious feeders and can strip off leaves and tender stems very rapidly, moving into pods when not controlled.

“The mistake is for producers to wait too long before they spray,” says Monti Vandiver, a Texas AgriLife Extension integrated pest management (IPM) specialist in Muleshoe. “It’s one of those pests that are easily remembered by people who have seen what they can do. They can be devastating, but can be managed.

“Typically, they can be controlled most effectively when they are a half-inch long or smaller. But if they get too large, they are difficult to kill. Sometimes you see mixed populations with small and large worms. If you can kill 90% of the small ones, you still might not get adequate control of the entire population.”