Knowledgebase

Lilac disease #780612

Asked January 22, 2022, 10:03 AM EST

I have 12 lilac bushes. Some of them have that blight /disease I trimmed them back to about 3 feet. I was wondering if I needed to trim them back to the ground. To Try to get back my healthy shrub Thank you very much for helping me out

Carver County Minnesota

Expert Response

Hello Joanna, happy to help.

Leaf blight diseases are best controlled by removing the affected leaves.  Affected leaves that have dropped to the ground can overwinter the fungi.  When the spring rains and winds start up, the spores from these fungi can reattach to the new leaves and start the process all over again in the right conditions.

The best control method is to clear out all the leaves that have dropped from affected shrubs to prevent reinfection.  In your case, if you haven't done that last fall, I recommend doing it as soon as you can get underneath and around the shrubs.  There is no need to prune your shrubs any more than you already have.

If the disease is caused by fungi, the above applies however, there are other possible leaf spot disease organisms such as bacteria that you should be aware of; so if after reading the following link about leaf spot diseases you don't think it's fungi, then I recommend sending newly affected leaves to the U of MN Plant Disease Clinic for a diagnosis.  The previous sentence contains their link where you'll learn about their services, prices, and how to submit a sample.

Good-luck! 
Ellen Campbell Replied January 23, 2022, 9:48 AM EST

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