lilac blight

Question: Greetings,

I have a number of mature lilacs (over 30-40 years) on my property in Ann Arbor and they're all experiencing some kind of blight.  How might I respond, please, hoping that they bound back in spring 2025?

Thanks for your time.

responder: An Ask Extension Expert Replied August 19, 2024, 12:40 PM EDT
response: Hello,  It sounds like your lilacs may be suffering from bacterial blight caused by the bacterium Pseudomonas syringae pv. syringae. This can be a severe disease, especially in cool, wet springs. More information at this link:  How to recognize, treat and avoid lilac bacterial blight | OSU Extension Service (oregonstate.edu)  Here are some steps you can take to help your lilacs recover and prepare for a healthy spring in 2025:  Prune Affected Areas: Prune the blighted shoots well into the green cambial tissue, making cuts at least six to eight inches below any visible signs of infection. This removes the diseased tissue and stimulates lateral bud development for new shoots.  Disinfect Pruning Tools: Clean your pruners with a disinfectant between cuts to prevent the spreading of the infection. Remove and Destroy Infected Debris: The tissue pruned out or falls as leaf litter is still infectious and should be removed from the area and destroyed.  Avoid Overhead Irrigation: If practical, eliminate overhead watering to prevent the bacteria from spreading to healthy tissue. Improve Air Circulation: Ensure good plant spacing to reduce short-distance spread and promote more rapid drying of the foliage.  Consider Copper Fungicides: While not a sole solution, copper fungicides are known to be somewhat inhibitory to Pseudomonas bacteria and could be used as part of an integrated management approach.  Remember, never prune when leaves are wet or during wet weather, as this can facilitate the spread of the disease. It’s also important to note that plants infected with Pseudomonas tend to be more susceptible to freezing, so protecting them from late frosts can also be beneficial. More information at these links:  Bacterial blight of lilac - MSU Extension  Lilac: An old-fashioned, favorite shrub - MSU Extension  For a confirmed and precise identification of the problem, I recommend you send all your images by e-mail to the MSU Plant & Pest Diagnostics Lab.  The experts there can also provide you with the best treatment options.  Their email is <personal data hidden>.  Please include your name. The lab will let you know if they need a sample sent. FYI, the lab may also ask for additional images.  Their website is at this link:  Plant & Pest Diagnostics (msu.edu)  Their Contact Information is at this link:  Contact Us - Plant & Pest Diagnostics (msu.edu)  This link will explain the details of submitting a sample to MSU Plant & Pest Diagnostics Lab:  Submit Samples - Plant & Pest Diagnostics (msu.edu)  I hope this helps!

responder: The Question Asker Replied August 19, 2024, 12:45 PM EDT
response: Thank you for your response.  To be sure, can I prune now (if it's dry) or must I wait until winter when the lilacs are dorminant? HansOn Mon, Aug 19, 2024 at 12:40 PM Ask Extension <<personal data hidden>> wrote:

responder: An Ask Extension Expert Replied August 19, 2024, 1:25 PM EDT
response: Hello again,  Lilac shrubs are best pruned right after blooming and when dry. You don't have to wait until winter.