Many times a tree has been starved by salts from quick release fertilizers put down on lawns. High salts in many fertilizers can actually pull moisture and essential elements out of the root system. The tree cannot feed itself and one of the early signs is crown dieback. If caught in the early stages, injections of essential elements directly into the tree by a Certified Arborist can save the tree. In the meantime, eliminating the high salt fertilizer from the feeding area of the tree can give the area time to drain the salts away.
The tree then has a chance to regain its ability to draw moisture and essential elements from the soil. If recovery is successful, your ISA Certified Arborist can institute a slow low salt fertilization program.
Have an evaluation report done on all of your trees by an ISA Certified Arborist before hiring a tree service.