Last spring I planted a small crabapple and it's been doing great. Last night I noticed that all the leaves on the top half of the central leader have turned brown and shriveled. There are a couple of other places on other branches that are starting to do the same thing. I don't see any insects, etc that would be the cause. Some of the leaves that haven't turned brown do have some spots.

Any ideas on what I can do to save it?

Thanks in advance.