It is really important that you know for sure which disease you are treating before you treat it. Blight, itself, is not a disease, but rather a symptom, which can be caused by different pathenogenic organisms, either bacterial or fungal. The treatments for each may not work for the other. You can take samples of affected material to your local extension service to get a diagnosis of which pathogen is responsible. The following link, especially entries #25 - #29, refers to a diagnosis of Botrytis cinerea, a bacterial blight: http://www.botanicalgarden.ubc.ca/forums/showthread.php?t=14735. Let us know if you have further questions.
