CropLink

Some pests have a lot of nerve.

Shelby, Iowa, farmer Wayne Martin was already feeling jinxed during the 2018 growing season. And, just when hail, Japanese beetles and green snap seemed to be the last straws, a perplexing soybean pest came to call.

No one knows much about soybean gall midge. The first sign of trouble is the soybean stem turns brown and will look slightly swollen at the soil line.

“Peel back the skin of the stem, and you’ll find a bunch of little red maggots,” Martin says.

“Their feeding forms a gall--or a scar--as if the plant may be trying to compensate. Eventually, the bugs win out, and the stem looks as if it has been put in a vise at one distinct point. It shrivels and turns brown, and the plant breaks off.”

Iowa State University entomologist Erin Hodgson says there were some isolated reports of soybean injury by soybean gall midge in northwest Iowa in 2016 and 2017. There have been other confirmations in past years in Nebraska and South Dakota. The pest appears to be building momentum, though.

The damage in Martin’s fields has been most heavily concentrated along field edges. The plants first look as though they are wilting down, but it doesn’t take long for them to go into full tilt distress. The maggots start out creamy white and turn pink, and then red as they mature. “They are small, so hard to count, but I’ve found as many as 40 in one plant,” Martin says.

Hodgson says the adult form is a tiny, hairy fly and not known to be a good flier. “So we are seeing some edge of field pattern to their activity,” she adds. “However, so far, we’ve not found any other consistency linked to cultural practices.” Variety selection, fertility practices, row spacing and planting dates do not seem to influence the pest, she added. Insecticidal seed treatments also do not seem to suppress the pest.

[PF_0918]

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