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Soybean Gall Midge Is Damaging South Dakota, Nebraska, and Iowa Soybeans
As if soybean farmers didn’t have enough to worry about, there’s a new pest in the works. The soybean gall midge is damaging soybeans in northeastern Nebraska, northwestern Iowa, and southeastern South Dakota.
“Quite a few farmers in those areas are dealing with it,” says Gail Stratman, FMC regional technical manager in Stromsburg, Nebraska. “It has gone from affecting small areas into the thousands of acres in northeastern Nebraska. It is increasing in severity and geography.”
In Iowa, Iowa State University (ISU) Extension and Outreach entomologists have confirmed soybean gall midge infestations in 12 Iowa counties: Lyon, O’Brien, Clay, Plymouth, Cherokee, Buena Vista, Woodbury, Harrison, Shelby, Pottawattamie, Cass and Page.
Isolated damage reports from the soybean gall midge surfaced in northwest Iowa in 2016 and 2017. Its presence was first reported in Nebraska in 2011 and in South Dakota in 2015.
Little is known
So far, entomologists in these states know little about the soybean gall midge and have not yet been able to confirm the species.
ISU entomologists note midges are a fly in the Cecidomyiidae family, with 6,000 species worldwide. At least 1,100 species are in North America. Midges are small (.07 to .11 inches long), have long antennae, and have unusually hairy wings. Most midges are fragile and weak fliers.
Many midge species are considered economically important plant pests. However, some prey 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. This particular midge has larvae that are clear-color and eventually turn bright orange as they mature.
“Basically, they move into a soybean field and attack the outer edges first,” says Stratman. Some good news exists: At this point, infested plants seem to decline further into the field. University of Nebraska (U of N) entomologists randomly selected symptomatic plants from the field edge and found an average of seven maggots per plant. However, maggot numbers and frequency of infested plants decline rapidly with distance from the field edge. Still, field samples found infested plants were still present over 100 feet into the field.
ISU entomologists say this indicates that adults fly to new soybean fields following the growing season. Injury is usually restricted to the base of the plant. Initially, infested stems swell before turning brown and then breaking off, resulting in plant death. In some instances, plants were infected with a fungal disease, but this was not a consistent occurrence, say the ISU entomologists.
So far, cultural practices like variety selection, time of planting, row spacing, tillage, or manure application, do not appear to impact the soybean gall midge. Nor do insecticidal seed treatments appear to effectively suppress the midges. Entomologists think that the soybean gall midge can complete at least two generations in Iowa, but it is not known yet how long a generation takes to develop. It is assumed that it can overwinter in Iowa, and does so as a pupa in the soil or leaf litter similar to other midges.
Who to Contact
Iowa farmers who observe these midges infesting a soybean field in Iowa may contact Erin Hodgson, ISU Extension entomologist via email at firstname.lastname@example.org or on Twitter at @erinwhodgson.
Nebraska farmers who suspect gall midge damage in their fields can contact U of N entomologist Justin McMechan at email@example.com.
South Dakota farmers can contact Adam Varenhorst, SDSU Extension entomologist, at Adam.Varenhorst@sdstate.edu. If South Dakota farmers observe this pest, Varenhorst requests sending an image of infested plants along with the following information:
• Previous crop
• Tillage practice
• Seed treatments used
• Field edge issue or entire field issue