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Soybean Gall Midge

What may look like a fungal pathogen on the base of your soybean plants may be something else entirely. An insect called the “soybean gall midge” is damaging and killing soybeans in a growing number of Midwestern fields.

Erin Hodgson is an Extension entomology specialist at Iowa State University. She says it’s extremely difficult to see the adults, which are flies, but you can find the larvae. They’re on the inside of the soybean stem, generally three-to-four inches above the soil line.

"So, if you split a stem open, you’re going to see the larvae feeding on the inside, and the smaller larvae are hard to see because they’re clear, translucent," says Hodgson. "But as they mature, they darken up and the older larvae of course are bigger, but they also turn orange and they kind of look like a little mandarin orange slice."

Hodgson says larvae feed from June through August, with overlapping generations. They munch on tissue inside the stem, which restricts movement of water and nutrients to the upper part of the plant. The base becomes brittle and the plant falls over or breaks off.

She also notes that damage and plant death is mostly found around the field edges.

"And of course, that translates into yield loss, so I think when people are starting to think about harvest and they have all those jazzy yield-making map features now, if they happen to notice quite a bit of yield loss around the edges, that could be an indication that maybe they had midges and they didn’t know it," she says.

Not much is known yet about the insect’s biology and lifecycle, or how to control it.

Read more about the soybean gall midge

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