Soybean aphids attacking fields

WOOSTER, Ohio – A new insect that attacks soybean plants is keeping both researchers and growers throughout the Midwest on guard this season.

The soybean aphid, first discovered in the United States last year, has been found in fields again this year in such states as Wisconsin, Michigan, Illinois and Minneapolis.

Ohio hit, too. Counties in northwest, northeast, and southwest Ohio have reported the presence of the aphid, said Ohio State University entomologist Ron Hammond.

Although researchers are finding only a few aphids on the plants in most fields, there are instances where they are finding more than 100 aphids per plant on a few plants. In a single instance in Henry County, they found 1,000 aphids.

“It’s the first aphid known to colonize soybeans in this country,” said Hammond. “We know very little about the insect. This is fairly new thing, so we have no idea what will happen if it becomes a real problem. It’s causing some concern for growers.”

Hammond believes the soybean aphid, which is from Asia, may have been introduced to this country via other plant transports.

“It’s pretty widespread throughout the Midwest now, so we think it may have been here for about five or six years. We just hadn’t found it until now,” he said.

Feeds on plant. The soybean aphid is a sapsucker, feeding on the soybean plant and causing stunting, yellowing of the plant and leaf distortion.

If enough aphids attack a plant, they reduce the vigor of the plant, eventually leading to yield losses.

Researchers are currently surveying soybean fields throughout Ohio to determine how widespread the soybean aphid is.

How to scout. They are using a counting technique that requires analyzing soybean plants at the edge of the fields and counting the relative number of aphids on each plant. “We are using a scale of 0-3. Zero means no aphids, a one indicates up to 10 aphids, a two is 11-100 aphids, and anything over 100 aphids per plant is considered a three,” said Hammond.

Hammond said that if high populations of the aphid are present, researchers will study the insect to determine how it moves from field to field and analyze ways to control it, possibly with beneficial insects or pathogens. “It’s hard to say what populations will cause serious damage to a plant,” Hammond said. “But we speculate that it will take thousands of aphids per plant to cause any kind of injury.”

Check new growth. Growers are recommended to scout their fields for the presence of the aphid with the same technique used by researchers, and examining 30 plants for about 45 seconds in each field.

“If you turn over the upper leaves, especially the new expanding ones, that’s where the aphid will be. If they are present, you will see them in the couple of seconds it takes to examine the plant,” he said.

A hand lens will be required to correctly identify the aphid. It looks like any other kind of aphid, but the adult is similar in size to a small potato leafhopper nymph, so correct identification is essential.

“But if you find an aphid actively feeding on the plant, then it’s assumed that it’s a soybean aphid because at this point in time that’s the only thing we know it to be,” Hammond said.

Not at treatment threshold. Growers should not take action toward treatment or control at the first sign of aphids. It will take a lot of aphids to cause problems, and Ohio is not there yet.

Those who find soybean aphid infestations in their fields should contact their local county Extension office. Hammond asks that growers who find high populations of the soybean aphid contact him directly at 330-263-3727, or e-mail hammond.5@osu.edu.

“At this point in time, we are definitely recommending a ‘wait-and-see attitude’, but growers need to be aware that there may be a potential pest on the horizon,” said Hammond.

“Growers should stop every so often and look at the plants and make sure nothing seems out of the ordinary. We want to stay on top of the situation and not get caught holding the bag come August if problems do develop.”