Soybean aphids found in northeast Arkansas

Soybean aphids have been documented in Arkansas for the first time. The discovery in two northeast counties wasn't a “huge surprise” for Glen Studebaker, Extension entomologist.

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

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

“He wanted to know if they are soybean aphids. We confirmed they are. 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 was out looking at the plants, turning over leaves. That's when he found the aphids and suspected they might be causing the problem. If that field hadn't had SDS, we might not have known the aphids had arrived in the state.”

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

“A consultant found several colonies. He sent some samples that confirmed it is the pest. We're looking in adjacent counties but haven't found any more.”

Studebaker hopes beneficial insects will take care of the aphids. “A lot of the aphids 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 Midwest threshold numbers (250 aphids per plant).

“Since we're not seeing crop damage, we're playing it by ear. Some larger plants 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 less the potential yield loss from soybean aphids. That's another reason we aren't so quick with an application.”

Soybeans aphids shouldn't be able to overwinter in Arkansas. The pest's 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 next year. We've gotten our wake-up call.

“If growers find any aphid colonies in their soybeans, they should 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 farther.”

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