Answer: Lilacs are subject to a number of bacterial and fungal infections and it sounds like this is what has happened during this moist spring. Trim out any of the infected leaves along with any stems that might have lesions on them. Clean your pruner in a solution of one part household bleach to nine parts water in between cuts. Next, prune the top to allow good air circulation, and thin out the base for the same reason. Remove any suckers smaller than a pencil, too. Lilacs do best in full sun with good air circulation. Finally, avoid giving the plant an excess of nitrogen, as this can encourage the problems.
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