We are still receiving confirmations of gall midge in South Dakota and the number of counties where this pest is present continues to increase. However, as soybean begins to senesce, using discoloration around field edges will no longer be viable for finding infestations. While at the South Dakota State Fair we received many reports of fields that are being affected by gall midge. As the season progresses, fields with lodged soybean should be scouted to determine if the lodging is due to gall midge activity. Although color may not be as useful now for scouting, the presence of a white saprophytic fungus at the base of the plant can still be used to find potentially infested soybean (Figure 1). Also, lodged soybean plants that are breaking off near the soil surface can aid in finding this pest within a field (Figure 2).
Figure 1. White mold present on gall midge larvae infested soybean stems. Courtesy: Adam Varenhorst
Figure 2. Soybean that snapped off when slight pressure was applied to the top of the plant. Courtesy: Adam Varenhorst
When this fungus is observed on a plant the gall midge larvae are almost always present. Gall midge larvae have been confirmed in Clay, Codington, Davison, Deuel, Douglas, Edmunds, Hamlin, Hanson, Hutchinson, Kingsbury, Lincoln, Miner, Moody, Spink, Turner and Union counties (Figure 3). We are asking that everyone to take time to scout soybean fields for the presence of this pest as soon as possible.
The signs and conditions that have been associated with infestations include:
- Proximity to tree grove or shelterbelt.
- Proximity to previously infested field.
- Presence of white fungus on the base of the soybean stem.
- Soybean that snap very easily near the base of the plant.
- Discolored and swollen soybean stem near soil line.
- Presence of white to red maggots under the soybean epidermis in discolored regions.
Figure 3. Confirmations of gall midge larvae in soybean in 2018. Positive counties are shaded in red.
A reminder, the gall midge larvae vary in color from white to a dark red or orange color (Figure 4). They are small, but can easily be observed without magnification. The larvae tend to congregate around the discolored areas at the base of the stem (Figure 5). However, they may also be higher on the stem as well.
Figure 4. Gall midge larvae found in soybean. Courtesy: Adam Varenhorst
Figure 5. Gall midge larvae present on discolored portion of soybean epidermis. Courtesy: Adam Varenhorst
If you observe gall midge larvae, the easiest way to send us confirmation of the field is to email. an image of the infested plants along with the following information:
- Previous Crop.
- Tillage Practice.
- Seed Treatments Used.
- Occurrence in the field edge or entire field.