John, It sounds like your tree may have more than one problem. I do not diagnose tree problems as trees often have more than one issue weakening the tree. I recommend you have an onsite inspection from a certified arborist, a trained tree doctor. Best And Happy Yardening, Nancy.
Diagnosing River Birch Shrub Problems
Question From: J. Bliss - ILLINOIS
Q: I have a River Birch shrub that each spring looks as though it is getting attacked by some small insect.This causes a certain amount of leaves at the tips of branches to have tiny clumps of galls on them and discolor. If you look at the underside of the leaves infested, there is a white powdery substance, later in the spring there looks like there are tiny tiny flies around. Is this white fly and how do I treat the shrub. It is still healthy, although portions are being affected each year. It is a beautiful shrub and I would like to maintain it in our garden. Thank you, John Bliss