Soybean Tentiform Leafminer in Soybean
Crop Damage
The soybean tentiform leafminer (Macrosaccus morrisella) was first reported feeding on soybean in Canada in 2021. Since its discovery on soybean, it has been confirmed in six U.S. states (Iowa, Minnesota, Missouri, Nebraska, North Dakota, and South Dakota) and Canada. Larvae feed between the upper and lower surfaces of the soybean leaves, creating almost transparent mines. As larvae grow, the mines become larger, but the larvae avoid the leaf veins. Mined leaf tissue turns brown and eventually dies.
Pest Description
Larvae are 3/16 inches long and white. They turn from pale green to dark green as they mature. Adults are tiny moths that are approximately 1/4 inches long with distinct orange, white, gray, and black markings. They have fringes on the head and end of the abdomen.
Soybean tentiform leafminer larva.
Wayne Ohnesorg, Nebraska Extension-UNL CropWatch.
Adult soybean tentiform leafminer.
Wayne Ohnesorg, Nebraska Extension-UNL CropWatch.
Scouting and Management
There are no scouting protocols or management thresholds for soybean tentiform leafminers in soybean. Begin scouting early in the season, focusing on field edges that are near wooded areas. Carefully examine the underside of leaves, looking for the irregularly shaped blotch-like mines. As the soybeans develop, focus sampling on leaves in the middle to lower canopy. If leaf mines are present, scout the entire field and estimate the percentage of leaf area affected by mining. Because the mines kill leaf tissue, injury is currently being evaluated similarly to defoliation. Until soybean tentiform leafminer-specific thresholds are developed, use the standard soybean defoliation treatment thresholds as a general guideline: 30% defoliation during vegetative growth stages and 20% defoliation during reproductive growth stages.
Soybean tentiform leafminer is a new soybean pest and there are important considerations. If you suspect soybean tentiform leafminers in your field, contact your local or state extension specialists to confirm identification of this pest. This information helps to determine field abundance and spread into new states and provinces. Researchers are developing better scouting procedures, more accurate economic treatment thresholds, and effective approaches to manage this new soybean pest.
Developed and reviewed by Carol Pilcher, Iowa State University and Robert Wright, University of Nebraska-Lincoln, with support from the United Soybean Board.
Soybean tentiform leafminer larva.
Adult soybean tentiform leafminer.
STL larvae feeding on soybean causes trademark white blotches on the leaf.
Soybean tentiform leafminer pupae.
Gallery images courtesy of Wayne Ohnesorg, Nebraska Extension-UNL CropWatch.
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