We are receiving a lot of reports of small white, red, or orange maggots present under the epidermis of soybean plants. These maggots are associated with enlarged, woody soybean stems near the soil surface. The infested plants break very easily near the affected area. The maggots causing this issue are larvae of the gall midge (a kind of fly), and this isn’t the first time they have been observed in South Dakota. Although our initial observations were that gall midge larvae are simply feeding on secondary fungal pathogens, our neighbors in Iowa and Nebraska have reported the larvae feeding directly on soybean plants.
This transition in feeding behavior hasn’t been observed in South Dakota to date, but we are currently watching for it. When scouting soybean fields, monitor the base of stems for swelling and discoloration (Figure 1). If soybean plants easily snap while walking through them, this could be an indicator of a gall midge larvae infestation. Researchers at Iowa State University and the University of Nebraska have noted that the infestations they are observing tend to start near the edges of fields. If potentially infested plants are identified, peel back the epidermis to determine if the gall midge larvae are present. The larvae are small maggots and will vary in color from white (Figure 2) to orange or red (Figure 3).
Figure 1. Soybean plant with woody, enlarged area near the soil surface. Courtesy: Adam Varenhorst.
Figure 2. White gall midge larvae under soybean epidermis. Courtesy: Adam Varenhorst.
Figure 3. Orange gall midge larvae present on woody portion of soybean stem. Courtesy: Adam Varenhorst.
At this time there are no management recommendations for this insect. More research is needed to determine if gall midge larvae are feeding on the soybean stems, and what impact it may have on production. If you observe a soybean field with an infestation of gall midge larvae, please contact Adam Varenhorst.