Soybean tentiform leafminer in northwest Minnesota soybean

A survey trip last week of soybean fields in Red Lake, Pennington, Marshall, Roseau and Kittson Counties found the soybean tentiform leafminer (STL), a pest that until recently was only known to feed on two native plants in the same plant family as soybean, American hog peanut and slickseed fuzzybean. The survey trip focused on examining soybeans growing near trees as it is thought that this may be where STL survives the winter. 

Figure 1. The bottom of a soybean leaf with soybean tentiform leafminer mines on one leaflet.

 

While STL was found in Crookston at the Northwest Research & Outreach Center several weeks ago, during last week's survey, mines of STL (Figure 1) were found not in soybeans growing near trees in field windbreaks or shelter belts, but rather only in two soybean fields that were immediately (within 5 feet or less) adjacent to larger wooded areas. Figure 2 shows what the top side of the leaf mines in Figure 1 look like; this did have the 'tented' or raised appearance when the leaf is viewed from the top. One may easily miss seeing an infestation if leaves aren't being flipped over to check the bottom surface.

Figure 2. The upper surface of the soybean tentiform leafminer-infested leaf from Figure 1. Note the small pale green spots on the top leaflet and the slightly raised appearance.

Because it was only first found feeding on soybean in southeast Minnesota in 2021, UMN Extension soybean entomologist Dr. Bob Koch's research team is still working to determine whether yield losses are associated with the current levels of infestation. The team is also working to determine the geographic range of this pest throughout the soybean growing regions of the state and investigating whether insecticide treatment or other management techniques are warranted or effective. 

Here is a link for more information about Soybean Tentiform Leafminer.