Soybean Gall Midge Larvae in South Dakota Soybean

Scouting for Soybean Gall Midge

FIELD EVALUATION

Scouting for soybean gall midge can be as simple as looking for wilting or dying plants along field edges (Figure 1). However, it can be rather difficult if the plants are currently asymptomatic. If you have soybean that recently lodged, you should scout the plants to determine if soybean gall midge larvae infestations caused the lodging.

Figure 1. Wilting soybean that are infested with soybean gall midge larvae. 

STEM BASE

If your plants are currently asymptomatic, the first step is to evaluate the base of the stem near the soil surface. A soybean gall midge infested plant will be slightly swollen at the base with a noticeable brown discoloration on an otherwise tan/green stem. The stem will also have a noticeable scar from an early growth split at this area (Figure 2).

Figure 2. Soybean stem with slight swelling and discoloration near the soil surface.

DISCOLORED SITE

Once a plant with this characteristic is found, pull the plant from the soil and evaluate the discolored site for any signs of soybean gall midge larvae (Figure 3).

Figure 3. Evident swelling on soybean stem and dark brown discoloration present where a split had occurred on the stem.

BREAK POINT AND EPIDERMIS

Apply pressure above the discoloration on the stem and break the plant (Figure 4). Once the stem is broken, look for soybean gall midge larvae near the break point. Also, begin peeling back the epidermis in the discolored area on the stem.

Figure 4. Soybean stem that snapped immediately above discolored and swollen area. Notice the dark discoloration immediately around the break point.

LARVAE PRESENCE

When soybean gall midge larvae are present, you will find small white, pink or orange maggots on discolored areas of the epidermis and stem (Figure 5).

Figure 5. Soybean gall midge larvae present on discolored area of stem and epidermis after epidermis had been removed.