Thank you for your question.

I need some more information from you.  

1).  Please describe the extent of blooming that you saw this spring in the lilac?  Normal amount?  Any discoloration in the blossoms?

2).  When was the last time you did any pruning of the lilac?

3).  How old is the bush?

4).  To the best of your recollection, have you observed this leaf discoloration in past seasons?

We'll look forward to your response.  Many thanks.

1. The blooming was a normal amount with no discoloration on the blossoms
2. I pruned off a bunch of dead branches last year and a few little ones this spring.
3. I have no idea how old the tree is. I moved into the house in 2019. It seems like it has been here awhile.
4. I believe I noticed it last year, but I thought it was because of the drought. Once it rained, it seemed like the leaves perked back up.

Thanks for your question and response.

There are two common lilac diseases in Minnesota. I suspect that your bush is afflicted by one of them:

1). Bacterial Blight: This is 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 absolutely 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

I believe that this is the case for your lilacs. However for the sake of thoroughness, I’ll describe a second condition so that you can make a comparison.

2). Fungal Leaf Spot: This could be caused by either Cercospora or Septoria fungi. 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

As I said, I believe that your lilacs are experiencing bacterial blight. Besides cleaning up and removing all leaf debris, your lilac seems rather close to your house and has a “crowded” appearance. At this time (early July 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.

Good luck. Please get back to us with any further, related questions. Thanks for using our forum.



Glad to be of assistance.  Good luck with your lilacs!!