Answer: Your lilacs probably have powdery mildew, a common ailment in lilacs. Fortunately, the fungus, though unsightly, rarely causes any permanent damage. You can try thinning your plant lightly, pruning out some of the centermost branches, to increase air circulation. If you really want to get rid of the fungus, you can try dusting the plant with fine sulfur (a fungicide available at garden centers) -- follow directions and precautions on the package.
Q&A Library Searching Tips