Diseased common lilac Upper Sunshine Coast of B.C.
Did not take over this garden until mid-July so do not know how wet was the Spring. Quite hot since until last few days. Bush has reasonable air circulation and I intend to lower height and prune after leaf fall. Leaves have black/brown spots and on some these have converged to create complete complete black surface. I assume this is blight or leaf spot or both but they have only become apparent over the last six weeks, when removing spent blossoms. Our Winters here are similar to yours, usually quite wet and maybe a little cooler. Would it be worth applying a spray treatment? If so what would you recommend as there are may listed on your site. If left untreated would the disease re-appear next year. I find your website a good source of reliable information. Sincerely, Michael Sdwell, Powell River, B.C.
U.S. Minor Outlying Islands lilacs
Thank you for your question, Michael. We cannot diagnose plant problems without photos and, often, an examination of plant tissue. I suggest you contact the Botanical Garden: https://botanicalgarden.ubc.ca/advice/hortline-garden-advice/ Since they do not answer questions until Wednesday, you can compare your plant’s problems to those described in this Extension handbook: https://pnwhandbooks.org/plantdisease/host-and-disease-descriptions?title=lilac Good luck!