Emerald Ash Borer, dutch elm disease, maple wilt, disease control, tree treatments
A comprehensive guide to tree diseases
Problems in trees can be broken down in various ways.  If you are able to identify the tree that is affected you can diagnose the problem by cross referencing the signs you are seeing versus symptoms of the diseases that the tree can get.  This approach can be very difficult as trees have many diseases and often symptoms overlap and all problems must be ruled out to come to one disease.  The other approach is to break the symptoms you are seeing down into 4 categories and rule out 3 until you come down to a single problem source and then address the problem from there.  A more complex process will include parts for both approaches.  This process identifies the tree and breaks it down to one set of problems.  There ruling out diseases gets much easier.  In some cases you will just be able to identify the problem immediately by finding out what insect you are seeing infesting a tree.  Almost all approaches to disease diagnosis in a tree uses process of elimination approaches to determine the issue.
4 categories of plant problems
Texas  Tree Identification Guide
Click on Texas A&M forest service link above to properly identify your trees.