Hello,

Common lilacs, (Syringa vulgaris), are susceptible to many diseases including bacterial blight, leaf spots, leaf blight, powdery mildew and there are many insects that feed on its leaves such as lilac borer, lilac miner, caterpillars and scale. Also, lilacs prefer loose well-drained slightly acid soil. Read more here: https://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?taxonid=253923&isprofile=0&

https://extension.psu.edu/lilac-diseases

From the picture, it looks like your lilac has a rust disease but lilacs do not usually get rust disease. Also, the buds seem odd. It is, therefore, difficult to diagnose the problem from the picture. A proper analysis could be done at the MSU Extension Plant and Pest Diagnostic Lab. To learn how to submit a sample, go to: https://www.canr.msu.edu/pestid/ The diagnosis will include how to treat the problem.

I hope that this helps you with your lilac.

Thank you for contacting Ask Extension.