Fall armyworms have been invading Louisiana in recent weeks, and LSU AgCenter specialists expect the worms to hang around until cool weather comes in.

“I think they're worse this year than they have been in the past few years,” said Jack Baldwin, LSU AgCenter entomologist. “It's a statewide problem, and I expect them to be a problem until the first frost.”

Armyworms are invade fields, pastures and lawns. Populations can build very quickly and devastate a field overnight.

The pests can reoccur about every 30 days, so their numbers rise and descend throughout the summer and fall. But Baldwin said he isn't sure why the population is so heavy this year.

“There is no one thing to point to,” the entomologist said. “It seems like the last epidemic was during a dry year — and this year hasn't been all that dry.”

Matthew Stephens, an LSU AgCenter area agent in northeast Louisiana, said the worms have been destroying hay fields. “One field was ready to be cut when the worms came in,” he said. “One day it was a beautiful field, and the next day there was nothing to it. This field was expected to produce 1.5 tons per acre, and, at $60 a ton, that's a lot of money gone.”

The worms can be spotted early in the morning or late evening, Stephens said. High bird populations feeding early in the morning or late in the evening are indications of armyworms, the experts said.

“If I see an excessive number of cattle egrets or crows in a field, I look closely at the grass in that field,” Stephens said.

Baldwin said the best way to detect armyworms is to “just look for them,” using a sweep net or just visually inspecting.

How much damage is done depends on what stage the worms are in when they attack a field or lawn. “In their early stages, they are real small and don't consume much foliage,” Baldwin said. “But when they get large, they can consume a lot in a short time and do a lot of damage.”

Baldwin said sprays with Sevin, Confirm, Lannate, or methyl parathion will stop the armyworms quickly.