I say make like George Washington and cut down that tree - the Bliriana plum does not age gracefully and is a host to several leaf blights and insects. I have tried to rejuvenate this tree many times and the result is always rather fruitless. If you like the purple leaves, replace with a better behaved smoke tree. If the tree has sentimental value go ahead and try a fertilizer in the spring. Let me know if you get any great results. Keep growing, Marianne Binetti