Just had trees delivered today. My crape myrtle has back dots all over it. I called the nursery. She said its mold and won't harm the tree. Which may be true but does it mean anything else could be wrong with it?
You could contact your local city/county ag agent. Just to make sure it does not spread to other plants
If it is on small branches cut a piece off, put in a plastic and take it to a nursery. They will probably know.