This weekend I have noticed that whole branches of my Judas tree have brown leaves, and other (grrn leaves) have dropped. I have researched possible diseases but can't identify what is wrong. The tree otherwise looks healthy with lots of buds (presumably for next spring'd flowers). The affected leaves are dark brown and have black spots on the underside.
Photo available (tried to attach but failed!)
What is it, and what do I need to do to treat it?