Mississippi Soybean Infestation Turns Out To Be Caused By Something Other Than Hard-To-Control Soybean Loopers

Mississippi Extension workers breathed a sigh of relief today when it was determined that loopers causing economic damage in some Delta soybean fields are not hard-to-control soybean loopers but, instead, a more obscure pest, the gray moth looper.

The identification means that the loopers can be controlled with pyrethroids, which are less expensive than insecticides typically needed to knock down soybean loopers, said Angus Catchot, Mississippi Extension Entomologist.

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Loopers started turning up in fields last week and initially were thought to be cabbage loopers, which are easy to control with pyrethroids. But consultants and others in the field pointed out that the worms had black legs, which tend to indicate soybean loopers.

Catchot and other entomologists were perplexed because soybean loopers tend to show up later in the season.

Since last week, the number of reports grew, Catchot said late Tuesday afternoon.

“I’ll bet I’ve had 30 calls about this over the weekend and into Monday,” he said.

Catchot met with Drew consultant Tucker Miller and collected specimens from an infested field. He also conferred with Gus Lorenz, Arkansas Extension Entomologist, and Roger Leonard, Louisiana State University Entomologist.

Both naturally thought that these were cabbage loopers until Catchot said the worms consistely had black legs.

“Both of them realized that these weren’t cabbage loopers and said that it might, in fact, be the larval form of the gray looper moth, which is in the genus Rachiplusia.” said Catchot. “It’s a worm that’s around in small numbers and can be easily mistaken for a soybean looper.”

With that information, Catchot took the samples to Richard Brown, a Mississippi State University taxonomist and curator of the university’s well regarded insect museum. Brown confirmed that Catchot had, in fact, collected gray looper moth worms.

“We can tell folks now that they can go with a pyrethroid and don’t have to use an insecticde that's more expensive,” said Catchot. “Some fields already have hit the 35% defoliation threshold, and treatments have gone out. Before we made the identification, some growers probably did treat with something other than a pyrethroid, just to be on the safe side. But now we know that a pyrethroid will be appropriate.”

A few gray looper moth worms are being found scattered around the south Delta, he added, but the bigger numbers appear to be north of U.S. 82. Even then, they’re not solidly spread.

“You might have a 40- or 100-acre field that’s eaten up, but it will be surrounded by 1,000 acres that they’re not touching,” he noted.  “Everybody is finding them but not always at economic levels. Quite a few yellow stripe armyworms are out there, too.”

The worms likely are turning up in Arkansas, said Lorenz.

This is turning into a particularly "wormy" year in young soybeans in parts of the Delta. Our contacts this week report mixes of cotton bollworm (corn earworm) and yellow stripe armyworms in some fields, along with gray moth loopers.