Arkansas

A new-found insect pest in Arkansas, the soybean aphid, has the potential to rob farmers of yields, but an entomologist is counting on their biology and environmental factors to keep them under control.

Dr. Glenn Studebaker, entomologist with the University of Arkansas Cooperative Extension Service, told farmers at a meeting that the insect was found in 2004 in Clay County.

"A farmer's crop died from sudden death syndrome disease," he said. "The farmer saw aphids on the plants and thought they were killing his crop.

"We started looking more closely and found them in a lot of fields all across the northeast.

"We've been watching for them for years. But, so far, I've only seen cotton aphids on soybeans. The soybean aphid is similar looking to the cotton aphid. It's small, and the tail end of the aphid is light-colored, the same as the rest of the body. The cotton aphid has a dark color in that area."

Heavy soybean aphid populations can cause symptoms similar to potassium deficiency, and they're linked to viruses in soybeans.

The insect has the biggest effect in early reproductive stage beans. If they colonize soybeans at the right growth stage, they can cause a major yield drop. In Asia, farmers have seen up to a 30-bushel an acre yield loss with heavy aphid concentrations, Studebaker said.

The soybean aphid is a product of Asia like the recently discovered Asian soybean rust. The aphid was first found in this country in 2000 near Chicago.

The soybean aphid is the only aphid in the United States that will colonize and reproduce on soybeans, said Studebaker. "That's another giveaway to their identity," he said.

Studebaker thinks the insect won't be a problem in most years.

He said it overwinters as eggs on buckthorn plants. The eggs hatch in the spring, and the populations build up. Winds then help carry them into soybeans. The aphids move back to buckthorn in the fall.

Buckthorn only occurs north of Arkansas, starting in northern Missouri. The insect will have to move south each year to reach Arkansas. They're weak fliers, but storm fronts and prevailing winds can help them in their journey, the extension entomologist said.

Soybean aphids will find it difficult to reproduce in Arkansas.

"Seventy-seven degrees is the optimal temperature for them to reproduce," Studebaker said. "When it gets up to 95 degrees, which is not uncommon in Arkansas, they'll die within a few days. A cooler-than-normal August last year is probably why we saw them last year."

A cooler summer and prevailing winds, could cause a buildup in some Arkansas soybean fields, Studebaker said.

"I don't think they'll consistently be a problem in Arkansas, but insects do have the ability to adapt to changes. Should the aphid find a suitable host to overwinter in Arkansas, that could change the whole scenario. They would be showing up earlier in our production system."

In late planted soybeans in the early reproductive stage, there may be an isolated field from year to year that may be injured by the insect and need treatment.

"In the North, they treat on a field-by-field basis when the threshold reaches 250 insects per plant. We'll use the same threshold in Arkansas."

Studebaker said most soybean farmers will be in the field this year anyway looking for soybean rust, so it'll be a good time for them to also scout for this insect.

For more information about soybean insects, contact your county extension office. The Cooperative Extension Service is part of the U of A Division of Agriculture.

Date: 2/24/05

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