Certified GKH Gardening Expert
This, very much, looks like a Pestalotiopsis infection. There are many species, and they are all pretty devestating. ( I, actually, have a culture of Pestalotiopsis microspora in my own library! It eats plastic. Currently, I am working on sterilizing it so that it may do its job without being able to reproduce by spore.)
For now, fungicides and keeping the tree fed and healthy will be the only way forward. The spores are, ever-present, and won't infect a healthy specimen, usually.