Thanks for writing. I'm really sorry, but without being able to see your trees, I can't say for sure what the disease is or what the best course of action is.
Your best bet is to contact the staff at your local cooperative extension office. They should be able to help a lot more if you bring in samples of the affected leaves for them to review. If you're not familiar with your cooperative extension service, it's a wonderful resource. You can find contact information in the county government section of your telephone directory.
---Justin, Senior Garden Editor, BHG.com "