Lilac tree

Asked May 1, 2016, 5:06 PM EDT

My Lilac tree, which is more like a tall bush, hasn't bloomed in the last two years. This year it seemed to have a lot of blossoms but the leaves are starting to turn black. Do I have a diseases tree and should I remove the whole thing?

Blair County Pennsylvania

1 Response

The leaves turning black on your lilac may be the result of disease within the plant and may also explain the lack of flowering. It is likely environmental stresses on the plant, such as drought, heat, or cold, may have left the plant stressed and more susceptible to disease. The black leaves may be caused by bacterial blight (Pseudomonas syringae) or possibly Phytophthora shoot blight. In either case, treatment typically requires pruning out the infected branches back well below (12 inches) the diseased area, taking care to sanitize pruning tools between cuts. If the plant is heavily infected, you may need to remove the entire plant. Other treatment and cultural practices to rid the lilac of disease will depend on the specific disease. I recommend sending samples to the Plant Disease Clinic for a diagnosis. Samples should include both healthy and diseased parts, so cut sample twigs as mentioned earlier, well below the diseased area.

Instructions on submitting a sample to the Plant Disease Clinic can be found here:
http://plantpath.psu.edu/facilities/plant-disease-clinic/instructions
You will need to download the submission form to include with the samples when you mail them to the clinic.

For more information on lilac diseases:
http://extension.psu.edu/pests/plant-diseases/all-fact-sheets/lilac-diseases