Check out this link to see if this is what your tree has:
Hello. This link might be helpful. My maple gets it about this time every year too.
Take a leaf to your local County Extension Office, they’re free and they know.
It might be sooty mold. Here is how to deal with it: https://www.gardeningknowhow.com/plant-problems/disease/how-to-get-rid-of-sooty-mold.htm