Asked June 21, 2021, 5:58 PM EDT
Washington County Minnesota
This looks like a pretty heavy infestation of scale. See this: https://hennepinmastergardeners.org/scale-insects-take-a-closer-look/
Scale can actually kill the tree, and it is very difficult to treat. There are control methods in this article: https://hortnews.extension.iastate.edu/magnolia-scale
I’m sorry about your tree.