Question
I have a large mature oak tree that is shedding leaves, and acorns at an excessive rate.  Leaves are still green with some round brown spots on them and seem wilted.  They have been coming down heavily for the last week.

Answer
Hi there. This is a difficult one to diagnose without seeing the tree.
Here in New Jersey we are seeing our Oaks declining or suddenly dying from several problems:
1. drought from this and previous years
2. Bacterial Leaf scorch
3. 2 lined chestnut borer
4. Armellaria root rot and Phytophthora.
5. Sudden Oak Death (if you live west of the Mississippi.  
Just to name a few that cause these symptoms. Your best bet would be to call a Certified Arborist. Hope this helps,Bill