Soybeans are in bins for the season, but there are plenty of unknowns about a potential new pest.

With the discovery of soybean tentiform leaf miner (STL) in Madison County, Neb., on Sept. 27 by Nebraska Extension educator Wayne Ohnesorg, there are more questions than answers right now.

This native leaf miner (Macrosaccus morrisella) is known from two native plants: American hog peanut and sickleseed fuzzybean. Adults are very small moths — about 1/8 of an inch — with wings marked orange, white and gray-black. Ohnesorg says that STL has been observed in soybean fields, first discovered in fields in two counties near Minneapolis and St. Paul, Minn., in 2021.

The progression

The following growing season, it was confirmed in 10 additional counties in Minnesota and three counties in South Dakota. Five counties in North Dakota made the list in 2023, and Nebraska was the only state added in 2024, with a single infested field found in the northeast part of the state.

“We don’t know the extent of STL in Nebraska, so it’s difficult to tell if this is a pest across the soybean-growing areas of the state or confined to some areas,” Ohnesorg says. “There is a lot we don’t know. This insect has only been researched in soybeans since 2021, so the implication on soybean yields for 2025 are unknown.”

Related:How to test for soybean cyst nematode

A year ago, the University of Minnesota Extension reported survey results from summer 2023 that found STL in 77 fields across 44 counties in Minnesota and North Dakota. Besides Madison County, Neb., STL has been discovered in at least 51 counties in three other states so far, with most infestations occurring at field edges close to tree lines, the Extension says.

TRADEMARK: STL larvae feeding on soybean leaves is distinctive due to these white blotches.

The injury to soybeans is caused by larvae because they feed inside soybean leaves, forming mines that are first visible on the lower surface of the leaf and eventually also on the upper surface.

Life cycle

Eggs are laid on the underside of leaves, Ohnesorg says. Larvae — pale green to white — hatch and burrow into the leaf, where they feed on leaf tissue, at first in the form of a serpent-like mine and later growing into blotches or patches, with multiple mines on the same leaflet. Ohnesorg says mines don’t cross the midrib or major veins of leaves. Larvae, he says, will spin a silk retreat in the mine to pupate.

“What we do know is there are multiple generations each growing season,” Ohnesorg says. “There is an egg, larva, pupa and adult.” 

Learn more at cropwatch.unl.edu.