Please provide more information and pictures showing the problem if possible.  Are leaves falling and if so from what part of tree?  Did leaves not develop or come out of their buds this spring?  Numerous small holes in the leaves may be an indication of a caterpillar infestation.  Are full size leaves browning and falling starting at the top of the tree?  Anything you can share may help to diagnose the problem.

Thank you!
Bob