Thank you for your question.  it is difficult for us to diagnose the cause of a plant problem without knowing your location, and what care you have given the tree.  We don't know how much rain you have, what your soil condition is, or how often you fertilize and give supplemental water to it.  And, without a location, we don't know what type of diseases and insects are in your region.  Do you have a local horticulture university or other plant program with local experts?  Thanks!