Be on the lookout for a new soybean pest
By KRISS NELSON
Entomologists at Iowa State University Extension and Outreach have identified and confirmed the presence of the soybean gall midge in 12 counties across the state.
Those counties are Lyon, O’Brien, Clay, Plymouth, Cherokee, Buena Vista, Woodbury, Harrison, Shelby, Pottawattamie, Cass and Page.
Paul Kassel, ISU Extension agronomist, said he has personally found the pest near the town of Linn Grove in Buena Vista County.
This isn’t the first year the soybean gall midge has appeared in the area, as the pest happened to have a presence there in 2016 and 2017 as well.
In those years, there were some isolated reports of soybean injury as a result of the soybean gall midge.
According to ISU Extension, midges are a fly in the Cecidomyiidae family with 6,000 species worldwide and at least 1,100 species in North America.
Midges are small, just two to three millimeters in length, have long antennae and have unusually hairy wings. Most midges are fragile and weak fliers and are considered economically important plant pests.
However, some are predatory on aphids and mites.
Midge maggots are not mobile and must be located on or near the host plant to survive. Midge larvae feed within the host plant tissue, creating abnormal growths called galls.
These particular midge larvae are clear-colored and eventually turn bright orange as they mature.
“The larvae feed at the base of the soybean plant and create a gall – a big wound that will weaken the stalk, then the plant dies and/or falls over,” said Kassel.
At this time, not much is known about the soybean gall midge and, according to Iowa State University, entomologists have not been able to confirm the species as of yet.
Kassel said because there is little known about the soybean gall midge, they are unable to know what the economic threshold should be to go by before attempting to kill the pest, or even what, if any, insecticide is available to control it.
“The farmer that has these near Linn Grove, it’s his third year and he has tried different insecticides and what he applied didn’t work,” said Kassel.
But he said the good news is, by his experience, he has not seen the soybean gall midge infest an entire field.
As far as how the soybean gall midge came to Iowa, Kassel said they are unsure at this time, but entomologists in northeast Nebraska and southeast South Dakota are dealing with the pest as well.
Identifying soybean gall midge injury
Plant injury as a result of the pest has been most severe at field edges.
“It appears to often be present near grassy areas, terraces, waterways and near driveways,” said Kassel.
When scouting for soybean gall midge, he said to look for dead or dying plants near grassy areas. Chances are they will be scattered around in varying degrees of death with some being dead brown or some just wilted.
According to ISU Extension, injury is usually restricted to the base of the plant. Initially, infested stems look swollen, then eventually turn brown and break off, resulting in plant death. In some instances, plants were infected with a fungal disease, but this was not a consistent occurrence.
He also said to be on the lookout for plants that are breaking off at the soil line.
The pest can also be seen by the naked eye.
“It looks just like a house fly maggot and they often turn orange at some point in their life cycle,” he said. “The only advice we have right now is just to look. If you are out checking for soybean aphids, sudden death syndrome or walking beans to get some stray weeds here and there, just be looking for it.”
Kassel recommends if you find the soybean gall midge to contact your ISU Extension agronomist or associate professor and extension specialist in entomology Erin Hodgson via e-mail at email@example.com or on Twitter @erinwhodgson.
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