Lilac - Disease information and Management Recommendations. 
HOST PLANT DISEASE SYMPTOMS MANAGEMENT
Lilac 
Syringa spp.
Bacterial blight, Pseudomonas syringae pv. syringae Affects new growth. Lesions turn black and spread rapidly during wet periods. Tissue distal to the lesion shrivels and droops. White varieties are most susceptible. Remove infected plant parts using sterilized pruning tools. Space and prune plants to achieve good air circulation. Avoid overhead irrigation. Avoid wounds and plant stress. Do not overfertilize, especially with nitrogen.
CHEMICAL: Bordeaux (4-4-100), copper sulfate.
Powdery mildew, Microsphaera syringae Gray/white powdery fungal growth on the upper surface of leaves as well as shoots and buds. If severe, stunting and deformed growth occur. This fungus also attacks ash and privet. Space plants and prune to allow for good air circulation. Do not plant in shade. Avoid overfertilization. Water, but at the base and infrequently. CHEMICAL: Seldom necessary. Sulfur, thiophanate-methyl, triadimefon, triforine, or zyban.
These pages some times contain pesticide recommendations. Changes in pesticide regulations occur constantly, some materials mentioned may no longer be available, and some uses may no longer be legal. All pesticides distributed, sold, and/or applied in the USA must be registered with the appropriate State Department of Environmental Conservation (DEC). Questions concerning the legality and/or registration status for pesticide use in the USA should be directed to the appropriate State Cooperative Extension Specialist or your regional DEC office. 
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