KEISER, Ark. – Soybean aphids have been documented in Arkansas for the first time. Found in two northeast counties, the discovery wasn’t a “huge surprise” for Glen Studebaker, Extension entomologist with the University of Arkansas.

“We’ve been watching for them the last few years,” he says. “Even so, when you finally get word they’re here, you catch your breathe a little.”

In mid-August, a Clay County Extension agent called Studebaker (who is based at the Northeast Research and Extension Center in Keiser) about some suspicious aphids a farmer had found near Piggott.

“He was curious to know if they were soybean aphids. We traveled up there and confirmed they were. The populations aren’t huge yet and just from looking casually you can’t tell they’re present. There’s no damage, not much honeydew.”

Without crop damage, how did the farmer find them?

“It was a lucky coincidence,” says Studebaker. “The farmer had some Sudden Death Syndrome in his soybeans. He went out looking at the plants, turning over leaves. That’s when he found the aphids and suspected they might be causing the problem. He then called the county agent. If that field hadn’t had SDS, we might never have known these aphids had arrived in the state.”

Since the initial discovery, the aphids have been found in nearby Lawrence County as well.

“A consultant called and said he’d found several colonies. He sent some samples and those confirmed the pest. Now, we’re looking in adjacent counties but haven’t found any more.”

Studebaker hopes beneficial insects will take care of the aphids. “I’ve seen a lot of these aphids that were parasitized. That’s great, and hopefully it continues.”

Aphid numbers aren’t yet high enough for farmers to spray. Studebaker says he’s loosely adhering to Mid-West threshold numbers (250 aphids per plant).

“Since we’re not seeing crop damage, we’re playing it more by ear. Some of the larger plants I’ve seen probably had 250 but without the crop being hurt, we’re waiting a little longer.”

Studebaker says the 250-aphid threshold was developed on early reproductive soybeans. The host Arkansas soybeans – mostly Group 5s -- are “far past” that.

“Research shows that the further into the season a soybean crop goes the potential yield loss from soybean aphids decreases. That’s another reason we aren’t so quick with the application trigger.”

Soybeans aphids shouldn’t be able to overwinter in Arkansas. The pests’ ability to overwinter is tied to a wild host plant called common buckthorn.

“That plant, as far as I know, isn’t in Arkansas,” says Studebaker. “That leads me to believe that these populations will die off this winter. However, it wouldn’t surprise me to see them back here next year. We’ve gotten our wake-up call.

“If growers find any aphid colonies in their soybeans, please contact Extension and let us know. We don’t know how far south this pest will spread. Hopefully we’ll run out of season before it gets much further.”

e-mail: dbennett@primediabusiness.com