Just like people, trees sometimes get diseases that can shorten or even end their lives.  While some tree diseases have few practical solutions others can be addressed if caught early enough.  This page contains resources that can help you to identify tree diseases.  If you are still not sure what is wrong with your tree then consider contacting your county extension agent (http://www2.ca.uky.edu/county/) who can help get samples or images to specialists at the University of Kentucky.