Pictured: Soybean gall midge larvae. Photo by Justin McMechan UNL
Soybean field scouting in late July and August should include looking for two newer soybean pests: soybean gall midge and soybean tentiform leafminer.
No one has found either insect in Wisconsin to date. Both occur in neighboring Minnesota. Soybean gall midge was also recently found in eastern Iowa.
Soybean Gall Midge (SGM)
Earlier this week, officials confirmed SGM in Dakota County, Minnesota, just across the river from St. Croix and Pierce counties in Wisconsin. According to the Soybean Gall Midge Alert Network, the current known distribution of SGM includes 180 counties in seven Midwestern states (Iowa, Kansas, Minnesota, Missouri, Nebraska, North Dakota, and South Dakota).
In eastern Iowa, officials identified the recent SGM finds in Tama and Poweshiek based on wilted and dead soybean plants in the field margins. Adult gall midges are weak fliers that emerge and fly to the nearest soybean plants to lay eggs, usually infesting plants along field edges next to last year’s soybean fields. Symptoms to scout for are stems with blackened or discolored bases and deformed, stunted, or wilted plants. Infested plants become brittle and break easily along the stem. You can find the larvae by peeling back the epidermis tissue, as shown in the photo above.
How to scout: https://soybeangallmidge.org/scouting-for-soybean-gall-midge
Soybean Tentiform Leafminer (STLM)
A second new soybean pest to be alert for in late July and August is the soybean tentiform leafminer. Similar to SGM, infestations of this insect also develop along field edges, especially near wooded areas.
Signs of STLM on soybean leaves include raised, blister-like mines that form in a speckled oval pattern on the upper surface (refer to the leaf at the left below). On the reverse side of the leaf, the larvae feed internally between the tissues and form distinctive hollowed-out leaf blotches or mines (refer to leaf on the right).
Several mines can develop per leaf, and heavy mining may impact soybean productivity by reducing photosynthesis.
Report any suspected SGM or STLM infestations to the DATCP Pest Survey Program by emailing a photo to Krista Hamilton at Krista.Hamilton@wisconsin.gov.
Listen to a recent podcast with the DATCP Pest Survey Program:
