Soybean tentiform leafminer is a new pest to watch for

ST. PAUL — A new pest of soybean found in Minnesota in 2021 is the soybean tentiform leafminer. While this pest had been known to infest the native legumes American hog peanut and slickseed fuzzy bean across eastern North America, it had previously not been known to be a pest of soybean.

In 2021, soybean tentiform leafminer was found widespread in soybean fields across southern Minnesota and into eastern South Dakota.

Soybean tentiform leafminer adults are small moths (about the size of George Washington’s nose on a quarter) that lay their eggs on the underside of leaves. Upon hatching, larvae chew their way into the leaf tissue to form a linear “mine” as they tunnel within the leaf. As larvae molt and grow over time, they remain inside the leaves creating larger mines that are constrained by leaflet veins. As the larvae near maturity, the upper surface of the leaf where they have been mining becomes raised or “tented” and light colored spots can be seen on the upper surface of the leaf where light shines through small holes they make within the leaves. The leaf area that is fed upon by larvae tends to die, likely resulting in an effect on plants similar to that caused by defoliating insects.

In 2022, U of M Extension soybean entomologist Robert Koch’s team visited a soybean tentiform leafminer-infested field looking for additional information about this new pest. The team found that injury symptoms tended to be greater toward the bottom of soybean plants and on field edges near wooded areas. A survey effort during the 2023 growing season will help to reveal how large of a footprint soybean tentiform leafminer currently has on the Minnesota landscape.

While more research is needed, Koch said, “We have found several species of parasitic wasps feeding on soybean tentiform leafminer attacking these caterpillars inside the leaves. We’ve also done some preliminary work with insecticides with translaminar (ability to move from one surface of a leaf to the other) activity, and we’ve seen fairly good levels of control in some assays using potted plants for control of early stages of the caterpillars; but we need to expand that work to actual real-world in-field infestations.”