KANSAS CITY (B)--It is not autumn, nor is grass their usual food, but that seems to matter little to hordes of fall armyworms that have begun to munch on pastures in northeastern Kansas, causing heavy forage losses in some areas.
"I have seen infestations of 20 armyworms per square foot (and) in some spots, the vegetation is almost gone," said Kansas State University entomologist Leroy Brooks. "So far, brome pastures in Riley, Nemaha and Brown counties appear to be the worms' primary targets. But, we have also had damage in at least one alfalfa field and some forage sorghum."
The problem could continue until early fall, Brooks warned. And he adds that ranchers who don't scout their grassland immediately may not notice armyworm damage until too late--after most of the damage is done and treatment no longer is cost-effective.
"For numbers of this magnitude, they are arriving unusually early," Brooks said. "And, fall armyworms can produce up to three generations per growing season."
KSU entomologist Randall Higgins added that armyworm "infestations in grass are fairly rare."
The pests are described as blackish with yellow stripes, ranging from 0.50 inch to more than one inch long.
"That means the larvae will be active for just four to seven more days, because when the worms reach about 1.5 inches long, they gradually stop feeding," Brooks said. "Their destructive stage of development lasts only 14 to 16 days after hatching."
After that, the pests crawl into the soil to pupate and emerge later as a new brood of egg-laying moths, the entomologists said.
"New adults may remain in the vicinity, but they generally fly to a new location," Brooks added. "As a result, the threat of new infestations in grass, late sorghum or corn, alfalfa, and early-planted small grains can extend into October."
He recommended spraying for fall armyworms when grass infestations reach an average of about four to five "half-grown, healthy worms" per square foot.
Only a limited number of pesticide products are registered for pasture use and some require a waiting interval before grazing or harvest for hay.
The last extensive outbreak of fall armyworm lasted from August into early October 1998, hitting areas from Louisiana, into Texas and as far north as eastern Kansas.
"We never know if they are going to produce several generations or sort of fade away," Brooks said. "Armyworms like a multitude of plants. At the same time, though, a multitude of parasites--especially different kinds of flies and wasps--like fall armyworms."
A weekly crop-weather report issued Monday by the Kansas Agricultural Statistics Service rated 42% of the state's rangeland in good to excellent condition, down from 46% on July 10.