Lilacs turning brown and falling off - Ask Extension
My lilacs leaves have turned brown, curled up and are falling off. I know we've had a lot of rain. Could this be the cause? Thanks
Knowledgebase
Lilacs turning brown and falling off #879086
Asked July 28, 2024, 10:00 AM EDT
My lilacs leaves have turned brown, curled up and are falling off. I know we've had a lot of rain. Could this be the cause? Thanks
Goodhue County Minnesota
Expert Response
Thank you for writing.
Many of you are experiencing lilac blight where the leaves of your lilacs are going brown, almost as if they are charred. My lilacs have this condition as well. It could be aggravated by the rain and heat this summer.
This is a combination of my advice, advice from various University websites and from Hort Professor Emeritus Dr. Stephen Hedman
Lilac blight is extremely common in the Metro area. Some comments:
1). It could be caused by a bacterium Pseudomonas syringae which has leaf darkening, leaf wilting, and leaf dropping. This is largely a cosmetic condition and unless it occurs for several years has no adverse effects. It is associated with wet conditions, as during this summer. This is NOT a fungus; fungicides are of no use. It can be transmitted from one season to the next via leaf debris. Thus, to prevent transmission thorough fall cleanup is essential. See here for information https://extension.umn.edu/plant-diseases/leaf-spot-diseases-trees-and-shrubs#bacterial-leaf-spots-and-blight-1156513andhttps://yardandgarden.extension.iastate.edu/encyclopedia/lilac-bacterial-blight#:~:text=Symptoms%20of%20lilac%20bacterial%20blight,Eventually%2C%20leaves%20may%20be%20killed.
and https://extension.oregonstate.edu/news/how-recognize-treat-avoid-lilac-bacterial-blight
2). It could be caused by Cercospora or Septoria fungi. The symptoms are small, brown to black spots appearing on lilac leaves that are surrounded by a yellow halo. The leaves will become distorted and drop prematurely.
See: https://extension.missouri.edu/media/wysiwyg/Extensiondata/Pro/PlantDiagnosticClini
c/Docs/leaf-spot-on-lilac.pdfandhttps://yardandgarden.extension.iastate.edu/article/2021/08/summer-foliar-lilac-diseases
3). It is not important which type of blight it is; it should not kill 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.
If you must know what disease you have, you can send a sample to: https://pdc.umn.edu/
4). There is not much you can do to make your lilacs look normal. Thinking ahead to the 2025 season to prevent a recurrence of this blight. Besides cleaning up and removing all leaf debris.
5) Many lilacs have not had proper pruning for several years and need some rejuvenation pruning.
a) Remove dead wood and volunteer trees and bushes.
b) Cut off 1/3 of the largest stems (approximately up to a third of the plant) 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.
c) Repeat b for two years. Allow the smaller shoots to grow up, essentially creating an all new lilac.https://holdenfg.org/blog/rejuvenation-pruning-of-lilac-bushes/
6). Send all plant debris to the city lawn waste pickup. Do not compost them!
Many of you are experiencing lilac blight where the leaves of your lilacs are going brown, almost as if they are charred. My lilacs have this condition as well. It could be aggravated by the rain and heat this summer.
This is a combination of my advice, advice from various University websites and from Hort Professor Emeritus Dr. Stephen Hedman
Lilac blight is extremely common in the Metro area. Some comments:
1). It could be caused by a bacterium Pseudomonas syringae which has leaf darkening, leaf wilting, and leaf dropping. This is largely a cosmetic condition and unless it occurs for several years has no adverse effects. It is associated with wet conditions, as during this summer. This is NOT a fungus; fungicides are of no use. It can be transmitted from one season to the next via leaf debris. Thus, to prevent transmission thorough fall cleanup is essential. See here for information https://extension.umn.edu/plant-diseases/leaf-spot-diseases-trees-and-shrubs#bacterial-leaf-spots-and-blight-1156513andhttps://yardandgarden.extension.iastate.edu/encyclopedia/lilac-bacterial-blight#:~:text=Symptoms%20of%20lilac%20bacterial%20blight,Eventually%2C%20leaves%20may%20be%20killed.
and https://extension.oregonstate.edu/news/how-recognize-treat-avoid-lilac-bacterial-blight
2). It could be caused by Cercospora or Septoria fungi. The symptoms are small, brown to black spots appearing on lilac leaves that are surrounded by a yellow halo. The leaves will become distorted and drop prematurely.
See: https://extension.missouri.edu/media/wysiwyg/Extensiondata/Pro/PlantDiagnosticClini
c/Docs/leaf-spot-on-lilac.pdfandhttps://yardandgarden.extension.iastate.edu/article/2021/08/summer-foliar-lilac-diseases
3). It is not important which type of blight it is; it should not kill 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.
If you must know what disease you have, you can send a sample to: https://pdc.umn.edu/
4). There is not much you can do to make your lilacs look normal. Thinking ahead to the 2025 season to prevent a recurrence of this blight. Besides cleaning up and removing all leaf debris.
5) Many lilacs have not had proper pruning for several years and need some rejuvenation pruning.
a) Remove dead wood and volunteer trees and bushes.
b) Cut off 1/3 of the largest stems (approximately up to a third of the plant) 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.
c) Repeat b for two years. Allow the smaller shoots to grow up, essentially creating an all new lilac.https://holdenfg.org/blog/rejuvenation-pruning-of-lilac-bushes/
6). Send all plant debris to the city lawn waste pickup. Do not compost them!
Thank you so much. Our lilacs flank both sides of our back yard and give us total privacy, but not so much now. You have been very helpful
