New weevil gnawing at Arkansas soybeans
Canadian Grain Commission Arkansas soybean growers are facing a new enemy -- the pea weevil -- an insect that hitched a ride from Europe in a legume used as a cover crop.
So far, the pea weevil’s presence is limited to just a few fields south of Marvell in Phillips County where Austrian winter field peas had been used as a winter cover crop. Farmers use cover crops to prevent erosion, hold moisture and add nutrients to the soil. The field peas, being legumes, help add nitrogen to the soil, thanks to a friendly bacteria living in the plant roots that fix nitrogen from the atmosphere.
The pea weevils have also been found in Louisiana and Washington State. In all three instances, “this pest situation is strictly related to this cover crop,” said Gus Lorenz, extension entomologist with the University of Arkansas System Division of Agriculture. “We’re introducing a problem with the cover crops.”
“It appears that the weevil is a legume feeder,” he said. “The immature form feeds on the nitrogen fixing nodules in the soybean roots.”
When the cover crop dies back and soybeans grow up through the residue, the soybeans - also a legume - become the weevil’s target. As adults, the weevils feed on the soybean leaves, leaving a most unique, scalloped pattern.
“It looks like you took some pinking shears and went around the edge of the leaf,” said Robert Goodson, Phillips County extension agent for the University of Arkansas System Division of Agriculture. “It’s a very distinct feeding pattern.”
The quarter-inch brown weevils have proven to be very hard to control, Lorenz said.
“As many as you see on the leaf, if you dig down into the cover crop residue, there’s a ton more of them,” he said. When a farmer applies an insecticide, it kills the exposed weevils on the plant, “and more come up and you have to spray again. It may take two or three applications or more to get them under control.”
Goodson said that, “right now, we’re working with the farmers to find the right control product and application timing to work on this insect. We’re talking about a product that has a little more residual action and trying to time the applications for when the weevils are out feeding and not under the residue refuge.”
Bevy of brown stinkbugs
The cover crop has created a second problem for area corn growers.
“Evidently, the winter field peas attract brown stinkbugs, so you get this big population under the cover crops and when farmers plant corn into it, the stinkbugs start feeding on the corn,” Lorenz said.
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