University of Missouri Extension confirmed Missouri’s second soybean tentiform leafminer find in Macon County on Aug. 19.
Ivair Valmorbida, the state crops entomologist, said in an Aug. 26 Extension release that the Macon County case is the state’s second. The first confirmed case was in a Cooper County soybean field in August 2025.
Valmorbida said farmers should scout soybean fields and call their local MU Extension agronomist if they think they have the pest. The Macon County office is at 111 N. Rollins St. Valmorbida can be reached at 573-882-6446 or ivairvalmorbida@missouri.edu.
The insect is a small white larva that turns pale green as it matures. Adult moths are less than one-quarter inch long, with orange and white wings marked in gray-black.
Adults lay eggs on the underside of soybean leaves. Larvae feed inside the leaves and make mines that do not cross the midribs or main lateral veins. The mined tissue dies and the leaf has less area.
On the underside, the mines become elongated oval white blotches. On the upper side they rise slightly, like a tent. The pest shows up mainly along field edges near forested areas.
The leafminer, Macrosaccus morrisella, was found feeding on soybean in Minnesota in 2021 and later in South Dakota, North Dakota, Iowa, and Nebraska. Valmorbida said it is native to North America and once fed on two wild legumes in the same family as soybean, American hogpeanut and slick fuzzybean.
There are no well-established management practices, the release said. University of Minnesota researchers have reported that parasitic wasps, other natural enemies, and translaminar insecticides could help. Potential damage is still unknown, Valmorbida said.
He is working with other universities to map where the pest is in soybean fields. His guide, “Soybean Tent Leafminer in Missouri Soybean,” is free at extension.missouri.edu/publications/g4444. Updates are also posted on CropWatch, a University of Nebraska-Lincoln site.