Fall armyworms are on the march in Louisiana, and heavy populations can cause significant damage to pastures, hayfields and lawns, according to Louisiana State University entomologist Jack Baldwin.

“Fall armyworms can have up to four generations per year in Louisiana, and each generation takes about a month to complete its life cycle from egg to adult moth,” says Baldwin. “In epidemic years, heavy moth flights can result in overlapping generations.”

The larval, or caterpillar, stage lasts two to three weeks, and full-grown larvae are about 1-1.5” long, brown to green in color with a prominent, inverted Y on the front of the head. They’re called armyworms because they move together in large numbers.

“Large caterpillars can eat most foliage in a field in just a few days,” says Baldwin. “If pastures are not scouted regularly, serious foliage damage from heavy infestations can suddenly appear.”

Farmers and ranchers can scout or sample for fall armyworms with a sweep net or by visual inspection of 1 sq ft of ground in several areas, he says. The economic threshold for well-managed pastures is one worm per sweep or one to two worms per square foot.

“Heavier populations can be tolerated if forage preservation is less critical,” he says. The insecticides recommended for fall armyworms in pastures include Sevin, methyl parathion, Lannate and Tracer.

In urban areas, homeowners can treat their lawns when fall armyworms threaten turf establishment or survival. “Bermudagrass would be the most susceptible,” says Baldwin. “Centipede and St. Augustine are less preferred but should still be considered at risk in an epidemic year.”

Insecticides included in the LSU AgCenter insect control guide for use on lawns include Acelepryn, Azatin XL, Battle GC, Mach 2, Lepinox WDG, Conserve SC, Talstar 10WP, Dylox, Condor XL, Crymax and Sevin.