Syringa vulgaris is the scientific name for lilacs, which are deciduous shrubs or trees. They are grown for their fragrant flowers that bloom in spring in shades of purple, lavender, pink and white. Syringas need well-drained, evenly moist soil in full sun to grow and bloom satisfactorily. They are easy to care for and have few serious diseases.
The fungus Botrytis causes gray mold, which can blight stems, foliage, buds and flowers on Syringas. During periods of high humidity, gray mold develops a thick layer of gray mycelium on infected plant tissue. The fungus lives in dead plant material and attacks weakened plant parts. Prune diseased or dead plant material, and clean debris from around plants, and destroy to prevent the spread of gray mold. Use a fungicide for gray mold on Syringas according to the manufacturer's directions to control the disease.
The bacterium, Pseudomonas, causes Lilac Blight. Infected foliage develops brown spots with yellowish halos, buds turn black and die before or right after opening, and new shoots droop and die. The disease spreads rapidly on young growth, but spreads slowly on mature growth. Use a copper-based product for Pseudomonas on Syringas following the manufacturer's instructions to control Lilac Blight.
A fungus causes powdery mildew and forms dusty white patches on infected plant parts on Syringas. Although the diseases attacks the foliage, stems, buds and flowers, powdery mildew is more unsightly than harmful. Infected leaves may grow stunted or curled, become chlorotic or drop prematurely, and infected flower buds may grow deformed.
Remove and destroy infected plant material from around and on the plant. The application of a fungicide for powdery mildew on Syringas at the onset of the disease may control it. Follow the manufacturer's instructions when apply fungicides.