Armyworms Destroying Crops, Grass Across Southeast

September 8, 1998

GAINESVILLE — The Southeast is suffering through the worst infestation of armyworms in recent memory, with the pests chewing their way through thousands of acres of crops, pasture and turf.

The insects’ population explosion was brought on by a mild winter followed by this summer’s drought, said Richard Sprenkel, pest management specialist with the University of Florida’s Institute of Food and Agricultural Sciences.

“They showed up very early but weren’t much of a problem in April, May and June because the drought stunted vegetation,” he said. “The rain that began in July activated fertilizer that had been lying dormant. Greenery exploded, and the worms went to town.

“Early in the summer, we were getting only four to five armyworms in our traps each night,” Sprenkel said. “Recently, we’ve gotten as many as 50 per night.”

The outbreak is serious throughout the Southeast, experts at universities in Alabama, Georgia, Louisiana and Mississippi said. “It’s the worst I’ve seen it in the 20 years I’ve been here,” said Lamar Kimbrough, a cattle feed expert at Mississippi State University in Starkville. “We’re concerned that the next wave will wipe out our winter ryegrass.”

Armyworms balloon from the width of two hairs to as fat as a pencil and up to 2 inches long during their three- to four-week life span.

“When they’re full-size, they move awfully quick, sometimes destroying a farm field in 48 hours,” said David Holmes, Marion County extension service director, in Ocala. “One farmer came in who said it was like his whole pasture was just moving.”

Armyworms are eating corn, cotton, peanuts and grasses used for pasture and hay.

“We’ve had some pastures so decimated that we’ve had to move cattle just to get them something to eat,” said Harrell Phillips, a veterinarian and farmer from Morriston.

The pests also are a serious threat to lawns, golf courses and athletic fields, stripping almost all the grass leaves, said UF turfgrass specialist Grady Miller. “They wiped out new plantings of grass at two Gainesville playing fields, and I’m getting calls from as far away as Louisiana.

“You can’t just assume one spraying of insecticides will solve the problem,” Miller said. “They have multiple generations, and the second generation can be worse than the first. It can catch you by surprise.”

The critters replace their skins, or molt, six times in their life span. “They do 90 percent of their damage in their last two moltings and go on overdrive the last 48 hours,” Sprenkel said.

The best weapon UF experts have found against armyworms is the new pesticide spinosad, which is licensed only for use on cotton. “It doesn’t kill most beneficial insects,” Sprenkel said. “When you use it, you don’t destroy the tiny wasps, spiders and various beetles that are armyworms’ natural enemies.

“Twice as many armyworms died in cotton fields treated with the new pesticide as in fields treated with other pesticides because the pests’ natural enemies helped out,” Sprenkel said. “We hope the new product will be licensed for use on other crops in the future.”

Farmers and ranchers should continue to check their hay fields and pastures for worms through September and October, said UF cattle feed expert Carrol Chambliss. “There already is a shortage of hay, and we need to apply pesticides whenever armyworms are spotted so we can harvest as much of this last cutting as possible.”

The armyworms should taper off in the fall as the weather changes and there’s less food for them because vegetation declines, he said.

“What we really need is a cold winter to kill back this year’s armyworms so we don’t have the same problem next year,” Chambliss said. “We hope this is just a bad year for armyworms and other pests, not part of a trend.”