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Soybean Gall Midge Adults Emerging in South Dakota

County map including portions of South Dakota, Minnesota, Nebraska and Iowa
Figure 1. Cumulative soybean gall midge adult captures. Courtesy: Justin McMechan, UNL.

Over the weekend a SDSU Extension collaborator reported that soybean gall midge adults had been captured in Southeastern South Dakota. These are the first adults that have been observed in South Dakota in 2020.

The highest counts were reported in northern Union county (Figure 1). However, adults were also captured in Clay and Lincoln counties.

The observation of adults emerging from last year’s soybean stubble indicates that the soybean gall midge larvae will probably soon be observed in this year’s soybean fields. The soybean gall midge adults are being captured through the use of modified corn rootworm emergence cages.

The soybean gall midge adults are small flies that measure approximately ¼ of an inch from the tips of the front legs to the tips of the back legs. The legs of the adults have alternating light (tan or yellow) and dark bands. They also have an orange abdomen (Figure 2).

Three images of a small fly on gray background and also present on a penny
Figure 2. Soybean gall midge adults. Courtesy: Justin McMechan, UNL.

These capture numbers can be used to inform foliar insecticide management decisions. If high capture numbers are being reported near you it is possible that a foliar insecticide treatment may reduce soybean gall midge infestation within your field. These treatments should be applied 2-10 days after emergence is reported. These treatments may protect yield to a degree, but infestation within the field is still possible.

Soybean gall midge larvae are normally observed in soybean that are V3 or later (three petioles with trifoliate leaves present on the plant). If your field is not at this growth stage, insecticides should not be applied to them. Observations from the last two years indicate that the soybean gall midge larvae require plants with natural injuries including stem cracks (fissures) that are present in V3 and later soybean.