Reader Question: Powdery Mildew on Lilac

Today’s Reader Question comes from Tommy in Halifax County, Virginia:

I live in an older home and there are lilacs growing on the property. Last year, their leaves turned almost white with some type of disease. Can you tell me what this was and if there is anything I can do to prevent it?

powdery mildew on lilac

Photo courtesy of

Tommy, it sounds like your lilacs (Syringa spp.) have a classic case of powdery mildew. Powdery mildew is a type of fungus that infects the leaves of many plants including dogwood, Monarda (bee balm), garden phlox and lilacs. It’s interesting to note that the parasitic fungi that infects one genus of plant will not necessarily infect other genera. Conditions that are favorable for powdery mildew growth include high humidity at night, low humidity during the day and temperatures of 70 to 80 degrees. That describes most springs in the Mid-Atlantic gardening region.

So what can you do to discourage powdery mildew on lilac?

  1. If you have the luxury of planting a lilac, pick a mildew resistant variety. ‘Miss Kim’ comes to mind immediately but I’m sure that there are other cultivars available.
  2. If you are going to be planting lilac, be sure to site them in an area with plenty of air circulation. If you have an area that always seems to be windy, this would be an ideal location for a new lilac.
  3. Lilacs will benefit from a sunny location to help the foliage dry before evening.
  4. In your case Tommy, one of the best things that you can do to prevent powdery mildew is thin the plant. By doing this, you’ll be helping the foliage to dry if you receive rainfall late in the evening or overnight.
  5. Speaking of rainfall and watering, don’t water in the evening. This watering rule pretty much applies to all plants, but it’s especially important with lilacs.


The last resort is to spray a fungicide. I don’t like chemicals in general so I don’t recommend going this route. Powdery mildew will rarely cause severe damage or kill the plant. Do everything that you can to promote healthy growth: add compost and mulch the plant to establish a deep root system. Enjoy the wonderfully fragrant blooms of the lilac and don’t worry so much about the powdery mildew. If you plant them in a mixed border, you’ll have other things blooming to distract your eye from the mildew.

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March 29, 2012Permalink 1 Comment