Bacterial Diseases:
There are two common bacterial diseases on woody ornamentals - Erwinia fire blight and Pseudomonas bacterial blight (also called bacterial canker). Fire blight attacks only plants in the Rosaceae family, such as apple, pear, cotoneaster, and rose. Bacterial blight or canker attacks many species; lilac and all Prunus species such as flowering cherry are highly susceptible. Once twigs dry out, it is virtually impossible to isolate the bacteria in the diagnostic lab, even though the symptoms may be strongly suggestive of bacterial disease. Only fungicides containing copper will help control bacterial diseases, but these may cause spotting or burn of young shoots in spring if applied at higher rates or under slow drying conditions. Prune and dispose of dead wood, disinfecting pruners as you go.

http://www.agf.gov.bc.ca/cropprot/landscape.htm