First detection of soybean tentiform leafminer prompts increased scouting in Wisconsin soybean fields.
Wisconsin agricultural officials have confirmed the first known detection of soybean tentiform leafminer (STLM) in cultivated soybean fields within the state. The Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP) reported the insect in St. Croix County on August 21, 2026, followed by additional findings in Polk and Pierce counties on August 25.
The detections occurred in northwestern Wisconsin, but officials currently describe the infestations as light. Based on the level of activity observed so far, soybean growers do not need to apply insecticides.
University of Wisconsin-Madison specialists are advising producers to continue scouting fields and monitor populations as the season progresses.
Laura Flandermeyer, Pest Management Outreach Specialist, and Emily Bick, Pest Ecology for Field and Forage Crops Extension Specialist, recommend regular monitoring to determine whether STLM populations increase and begin causing significant crop injury.
The soybean tentiform leafminer is native to North America. Although the insect has previously been found in Wisconsin on American hogpeanut and slickseed fuzzybean, both wild relatives of soybean, this is the first documented occurrence in the state's cultivated soybean fields.
STLM has gained attention as a soybean pest in other Midwestern states. It was first reported in Minnesota in 2021 and has subsequently been detected in Iowa, Missouri, Nebraska, North Dakota, and South Dakota.
Growers should watch for white, blotchy mines on the undersides of soybean leaves. Scouting should focus on field edges, especially areas near woods and dense vegetation. Producers are encouraged to inspect at least 20 plants within 10 feet of the field edge and record affected plants and leaves.
If infestations become severe, Wisconsin's soybean defoliation thresholds can guide management decisions: 30% during V1-R1, 20% during R3-R5, and 10% at R6.
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