Lilac bacterial blight
Thanks for your question. If your lilac died or you pulled it out because it was killed by Pseudomonas syringae, it should be noted that this bacteria can also infect a lot of other woody plants, including: pear, blueberry, cherry, maple, and others. If you plan on replacing it, it would benefit you to find plants or cultivars resistant to this disease if at all possible. One link that you may find of help with a lot of information about this disease is: http://pnwhandbooks.org/plantdisease/pathogen-articles/pathogens-common-many-plants/bacteria-and-oth... I am forwarding on your question to one of our disease diagnosis experts at OSU to see if he might have any other suggestions, as I could see no suggestion for treatment before future plantings and am not sure how long this disease can stay active in the soil.