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Loopers, stinkbugs hit soybean fields

Soybean loopers are beginning to show up in Arkansas soybeans — particularly in the southeast part of the state. While they are not a major threat yet, Arkansas Extension entomologist Gus Lorenz is warning farmers to watch out for the pest. The worms have been found as far north as Marianna.

“Soybean loopers are hard to control and they will eat a field clean in no time. Loopers are currently scattered throughout the southeast area, but numbers seem to growing. There's a lot of spraying going on. Intrepid and Tracer are the most common products used, although more Intrepid is going out because it's cheaper,” says Lorenz.

Complicating the situation is the continuing presence of stinkbugs. Controlling both stinkbugs and loopers in the same field is difficult. Part of the problem in dealing with both pests is in killing beneficials.

“Having stinkbugs and loopers in the same field is a bad combination. We can take the stinkbugs out with a pyrethroid but that can actually make the loopers worse. The reason is pyrethroids take out beneficials that normally beat up on soybean loopers.”

Producers with both pests are choosing between either a tank-mix or spraying twice. Either way, the treatments aren't cheap.

Soybean loopers are a tropical pest that migrate to Delta states from the Caribbean and extreme southern Louisiana. “When we get winds out of the Gulf of Mexico, loopers are blown into our neighborhood. That's why soybean loopers traditionally show up first in the southeast corner of the state and move up.”

Threshold levels are 25 percent defoliation. Lorenz says that generally equates to around 4 to 6 loopers per row foot.

“When soybean loopers get big they can defoliate a field in no time. A grower might check his beans on Friday and everything looks great. He heads off for some weekend fun, comes back on Monday morning and finds bald plants. That's how fast it can happen. Soybean loopers are absolutely voracious.”

Lorenz says there's a connection between cotton country and soybean loopers. The nectar produced by cotton plants is a fertility cocktail for loopers.

“When a female gets a hold of cotton nectar, it increases her egg-laying capacity 60-fold. It's amazing, but that's what happens. Without feeding on cotton, a moth may lay a couple hundred eggs. After feeding on cotton nectar, she'll lay 1,200 eggs-plus. That's why there's often such high numbers of soybean loopers around cotton.”

After seeing very high stinkbug numbers in spring wheat, Lorenz cautioned that the soybean crop could be threatened during the summer. As predicted, stinkbugs are now making themselves at home.

“We're seeing stinkbugs in a lot of Group 5 beans. The fields I've been looking at are running anywhere from two to three times threshold.”

Despite the high numbers of stinkbugs, Lorenz says the state is in better shape than a year ago. But while the numbers aren't as high, “that doesn't mean growers can relax. There are still plenty of stinkbugs that can do plenty of damage.”

Fall armyworms are also showing up in Arkansas pastures. Lorenz and colleagues are putting out tests and keeping a close eye on the situation.

“We've got significant populations of second generation armyworms. There's still plenty of time to get a third generation out there. We should see that third generation in two to three weeks. The good news is, we're getting really good results on the armyworms with 1 ounce of Tracer.”

Meanwhile, in Mississippi, “we haven't got many late beans, so we don't have to worry too much about soybean loopers. But there have been some spotted and fields sprayed. Most farmers are treating them with Tracer,” says Gordon Andrews, Mississippi Extension entomologist.

Andrews says some producers were thinking about treating the last week of August. Since then, however, soybean fields have dried down so much and so fast, “it wouldn't be worth it to treat. We see some loopers every year. This year, I'm seeing cabbage loopers, soybean loopers and green clover worms. But the levels aren't terrible and this isn't something that's sending producers off in a panic.”


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