A new threat to soybeans showed up in South Dakota this summer. “We received a lot of reports of small white, red, or orange maggots under the epidermis of soybean plants this summer,” says Adam Varenhorst, South Dakota State University Extension entomologist.

The maggots are associated with enlarged, woody soybean stems near the soil surface. The infested plants break very easily near the affected area.

FLY LARVAE: White gall midge larvae under soybean epidermis.

The maggots were the larvae of the gall midge (a type of fly). 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, Varenhorst says.

He recommends that when scouting soybean fields, monitor the base of stems for swelling and discoloration. If soybean plants easily snap while walking through them, this could be an indicator of a gall midge larvae infestation.

STEM FEEDERS: Orange gall midge larvae present on woody portion of soybean stem.

Researchers at Iowa State University and the University of Nebraska have noted that the infestations 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 to orange.

Source: SDSU Extension