Brown leaves on lilac bushes - Ask Extension
My 12 foot tall hedge of lilacs has brown leaves all over and they are falling off. I have heard varying responses - that it is a bacteria, a fungus ...
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Brown leaves on lilac bushes #881215
Asked August 12, 2024, 5:00 PM EDT
My 12 foot tall hedge of lilacs has brown leaves all over and they are falling off. I have heard varying responses - that it is a bacteria, a fungus or just too much rain. Solutions I have heard - cut down to the ground, cut down at least 2/3, thin out the bushes, just wait and see if it recovers next year.
What is your advice?
Thanks!
Hennepin County Minnesota
Expert Response
Many area lilacs have been suffering this year. And everything you've heard is true!
It could be bacterial, it could be fungal, and too much rain is certainly a factor:
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
https://yardandgarden.extension.iastate.edu/article/2021/08/summer-foliar-lilac-diseases
Cutting to the ground is a bit extreme, but lilacs are tough plants and usually survive such "rejuvenation pruning". A better approach, especially for an older, overgrown plant, is to take out 1/3 each year for the next three years, called "renewal pruning". Start with the oldest branches first and do it in the spring:
https://www.extension.iastate.edu/news/2006/jan/072602.htm
For now, thinning out the shrub and cleaning up fallen leaves slows any disease progression. And wait and see.
https://extension.umn.edu/plant-diseases/leaf-spot-diseases-trees-and-shrubs
It could be bacterial, it could be fungal, and too much rain is certainly a factor:
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
https://yardandgarden.extension.iastate.edu/article/2021/08/summer-foliar-lilac-diseases
Cutting to the ground is a bit extreme, but lilacs are tough plants and usually survive such "rejuvenation pruning". A better approach, especially for an older, overgrown plant, is to take out 1/3 each year for the next three years, called "renewal pruning". Start with the oldest branches first and do it in the spring:
https://www.extension.iastate.edu/news/2006/jan/072602.htm
For now, thinning out the shrub and cleaning up fallen leaves slows any disease progression. And wait and see.
https://extension.umn.edu/plant-diseases/leaf-spot-diseases-trees-and-shrubs
