My best guess is that it is some sort of scale. Maybe Lecanium scale. We have a gazillion native redbuds scattered through the woods, and I've never seen scale on them, but it is a pretty common redbud problem. And, honestly, there might be scale on my redbuds. I just don't wander around the woods looking at them because there are too many other critters roaming the woods that I don't especially want to run into.

Scale Management

Thanks, Dawn. It seems there are a gazillion kinds of scale. I'll take a clipping and put it in a ziplock bag and take to my local nursery for further identification.