Lilac Disease

Question: I have several mature lilacs on our property.  Many of them are losing leaves and perhaps worse.  I have attached pictures for your review.  These plants are on the north side of the house. I also have lilacs on the west side of the property away from the house, and some of those buses are also suffering similarly.
 
Several years ago I had a similar situation and I could not find specific treatment. I then sprayed the affected single bush with a dilute copper sulfate solution, and I thought that stopped the problem. Apparently, that didn’t work or I didn’t treat it sufficiently.
 
 I also have what I call a French lilac immediately adjacent to the originally diseased plant, and the French lilac does not appear to be affected. Can you please provide guidance as to how to treat the plants?  Thank you.

responder: An Ask Extension Expert Replied August 28, 2024, 9:48 PM EDT
response: Thanks for your question. I’m sure your lilacs have a blight. One type of blight is resistant to fungicides (copper sulfate) while another type of blight is sensitive. In short, that copper sulfate might have been effective a few years back does not confer any immunity to your lilac with respect to subsequent infections. I can’t give you a good answer as to why your French lilac is still healthy. Different varieties of lilacs have different resistances towards lilac blight. Hopefully, your French lilac will continue on its healthy course. As I just mentioned, I believe your lilac is experiencing a blight condition. This is now extremely common in the Metro Area. Some more detailed comments: 1). It could be a blight caused by the bacterium Pseudomonas syringae. Among other things, it is characterized by leaf spots that can lead to leaf darkening, leaf wilting, and premature leaf dropping. Fortunately, this is largely a cosmetic condition and unless it occurs over several seasons, there are no adverse effects. It is associated with wet conditions, which certainly describes our current 2024 season. Because this is NOT a fungal pathogen, application of fungicides will do no good. It can be transmitted from one season to the next via leaf debris. To prevent transmission from one season to the next, thorough fall cleanup is essential. See the following for further information and remedial procedures: https://extension.umn.edu/plant-diseases/leaf-spot-diseases-trees-and-shrubs - bacterial-leaf-spots-and-blight-1156513 https://yardandgarden.extension.iastate.edu/encyclopedia/lilac-bacterial-blight - :~:text=Management of lilac bacterial blight&text=Select varieties that have tolerance,bleach solution between each cut. http://plantclinic.cornell.edu/factsheets/lilacbacterialblight.pdf https://hort.extension.wisc.edu/articles/bacterial-blight/ https://extension.oregonstate.edu/news/how-recognize-treat-avoid-lilac-bacterial-blight 2). It could be a blight caused by either Cercospora or Septoria fungi. This may have been the type of blight you experienced several years ago. The symptoms are small, brown to black spots appearing on lilac leaves. The distinguishing feature of these spots is that they are surrounded by a yellow halo. Inspect your lilac leaves to see if this halo is present. The leaves will also become distorted and drop prematurely. See: https://extension.missouri.edu/media/wysiwyg/Extensiondata/Pro/PlantDiagnosticClinic/Docs/leaf-spot-on-lilac.pdf https://yardandgarden.extension.iastate.edu/article/2021/08/summer-foliar-lilac-diseases 3). It really is not important which type of blight exists; it should not be a fatal situation for your lilacs. Do not feel that they must be dug up immediately and discarded. They will recover although their blooming may be delayed by a season or two. You will need to be patient! However if you are curious as to which type of blight exists, consider submitting plant samples to a diagnostic disease laboratory for an analysis. This would be a definitive way of getting to the bottom of things. Both Wisconsin and Minnesota have excellent labs to do this. Before submitting anything to either of them, call first as to what type of samples should be submitted. Both have a nominal charge for their analysis. See: https://pdc.umn.edu/ https://pddc.wisc.edu/clinic-overview/ 4). There is not much you can presently do to make your lilacs attain a normal appearance. Your efforts must be more proactive, thinking ahead to the 2025 season to prevent a recurrence of this blight. Besides cleaning up and removing all leaf debris at this time (late August 2024), you could cut out a few stems to open things up. Do this cutting just above ground level. The objective is to improve air movement and circulation throughout the bush. This will help in decreasing the spread of the disease. 5). The sites previously mentioned will describe further proactive approaches. In short, they are: a). Remove and destroy infected plant parts, including fallen leaves and pruned branches, to reduce further spread of the bacteria or fungus. Lilacs are tough; they should withstand this removal. b). Prune the lilacs to improve air circulation and remove diseased branches. Make cuts well below the visible symptoms and disinfect (solution of one-part commercial bleach to nine parts water) pruning tools between cuts. c). Avoid overhead watering to minimize leaf wetness and reduce the spread of bacteria. Water at the base of the plants. d). Going into the fall, keep your lilacs well-watered and be sure to do a thorough cleanup of all plant debris. Good Luck. Please get back to me if you have further related questions. Thanks for consulting us.

responder: The Question Asker Replied August 30, 2024, 11:54 AM EDT
response: Thank you.  That is more information than I expected - and it will take most of the weekend to read and digest it.  Thank you again.     I may be back to you after the weekend.     Jerry  On 08/28/2024 8:48 PM CDT Ask Extension wrote:

responder: An Ask Extension Expert Replied August 30, 2024, 1:26 PM EDT
response: Glad to be of assistance.  Thanks for using our forum.

responder: The Question Asker Replied September 07, 2024, 3:38 PM EDT
response: Hello Ask Extension -     I appreciated your response to my recent lilac question that I took the opportunity to ask another question.  IN the meantime, I am arranging to get access to my shop vac to be used o vacuum up the lilac leaves which literally cover the ground under the plants.  We will see how that goes in the future.     However, yesterday, I had my granddaughter cut several branches off of a Lemony Lace Elderberry bush which is across the driveway and a bit further away from the nearest diseased lilac.  However, I had notices that the leaves on several of the branches of the  LL elderberry had virtually died up and down their stem. The dying leaves were nearest to the house wall, and the balance of the bush doesn't seem to be harmed thus far.       I will attach pictures of the branch that was cut off and another of the plant more generally. What is the problem here and is it perhaps related to the lilac issue.  The elderberry bush is three or four years old.     I would appreciate your guidance.  Thank you.     Jerry Leimer     On 08/28/2024 2:40 PM CDT Ask Extension wrote:  Dear Jerry, Thank you for using Ask Extension. A request for support has been created and a representative will follow-up with you as soon as possible. Questions are usually answered within two business days. You can view this question's progress online. YOUR QUESTION #0153260: Lilac Disease   I have several mature lilacs on our property. Many of them are losing leaves and perhaps worse. I have attached pictures for your review. These plants are on the north side of the house. I also have lilacs on the west side of the property away from the house, and some of those buses are also suffering similarly. Several years ago I had a similar situation and I could not find specific treatment. I then sprayed the affected single bush with a dilute copper sulfate solution, and I thought that stopped the problem. Apparently, that didn’t work or I didn’t treat it sufficiently. I also have what I call a French lilac immediately adjacent to the originally diseased plant, and the French lilac does not appear to be affected. Can you please provide guidance as to how to treat the plants? Thank you.    Ask Extension offers one-to-one expert answers from Cooperative Extension/University staff and volunteers within participating Land-Grant institutions across the United States. If you wish to provide additional comments or information regarding the issue, please login to your account for a complete archive of your prior questions and answers.  This message for informational purposes only. It is not intended to be a substitute for personalized professional advice. For specific local information, contact your local county Cooperative Extension office or other qualified professionals. eXtension Foundation does not recommend or endorse any specific tests, professional services, products, procedures, opinions, or other information that may be mentioned. Reliance on any information provided by eXtension Foundation, employees, suppliers, member universities, or other third parties through eXtension is solely at the user's own risk. All eXtension content and communication is subject to the Terms of Use which may be revised at any time.

responder: An Ask Extension Expert Replied September 12, 2024, 8:23 PM EDT
response: Thanks for your recent response. Yes, Pseudomonas syringae can also infect elderberries though not as severely as lilacs. Also, elderberries are susceptible to the same fungal pathogens that affect lilacs. All the steps, precautions, and remedial procedures I described for lilacs, are also applicable to elderberries. Think positively that the 2025 season will be an improvement from 2024. Good luck!! Thank you for your continued use of our forum.