By Blake Jackson
The Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP) has confirmed the first known occurrence of soybean tentiform leafminer (STLM) in cultivated soybeans in Wisconsin.
The pest was initially identified in St. Croix County on August 21, 2026, and additional detections were made in Polk and Pierce counties on August 25. The three counties are located in northwestern Wisconsin.
Current infestations are considered light, and specialists from the University of Wisconsin-Madison report that treatment is not necessary at this time.
Laura Flandermeyer, Pest Management Outreach Specialist, and Emily Bick, Pest Ecology for Field and Forage Crops Extension Specialist, recommend continued monitoring to track the pest's development.
STLM is native to North America and has previously been found in Wisconsin on American hogpeanut and slickseed fuzzybean, both wild relatives of soybean. However, it had not previously been documented in Wisconsin's cultivated soybean fields.
The insect has become a more recognized soybean pest elsewhere in the Midwest, with reports beginning in Minnesota in 2021 and later occurring in Iowa, Missouri, Nebraska, North Dakota, and South Dakota.
The most noticeable symptom is white, blotchy mining on the undersides of soybean leaves. Small, pale larvae feed inside the leaf tissue, creating mines that do not cross the midrib or major veins. Speckling may appear on the upper leaf surface. Adult moths are very small and generally do not cause plant damage.
Growers should concentrate scouting along field edges, particularly near wooded areas and dense vegetation. Examine at least 20 whole plants within 10 feet of the field edge and record the number of plants and leaves showing mines.
For now, insecticide applications are not recommended. If severe infestations develop, growers should use Wisconsin soybean defoliation thresholds: 30% during V1-R1, 20% during R3-R5, and 10% at R6.
Photo Credit: gettyimages-gilaxia
Categories: Wisconsin, Crops, Soybeans