Hello Ned,

Are you able to send us a photo or two of the symptoms separate from the screencap with the A.I. diagnosis? A photo of both the upper leaf surface and the underside would be helpful. They look less like a leafminer mine (though "blotch" type mines do occur on a variety of plants) and more like eriophyid mite feeding injury called a felt/velvet gall. Birch can be a host, as can a variety of other trees. It's also possible both mines and mites are present.

Fortunately, neither condition -- leafminer or mites -- needs intervention, nor would attempting to treat a shade tree be practical, given its size and the amount of pesticide that would be needed. They will not harm the tree, and if you prefer, fallen leaves this autumn can be collected and disposed of to potentially interrupt the life cycle of the organism responsible so an outbreak isn't as abundant next year.

If you're able to send additional close-up photos, we'll try to determine which condition this is.

Miri

Thank you for the additional photos. Although we can't see the leaf upper surfaces, which would help to confirm a diagnosis, the patches do indeed look like felt galls caused by mites. Overall, the tree looks healthy, as you noted, so we are not concerned. The mite population may crash in future years and symptoms of their activity will not be visible at all, or at least be minimal, as pest populations naturally rise and fall across several years. Despite how abundant they are now, they aren't causing the tree much stress. (Of more stress to the birch would be drought, like we experienced last year, unless the root zone can be periodically watered during dry spells. River Birch are notorious for shedding some leaves in summer if the weather stays dry for a stretch.)

Miri