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Powdery Mildew on Lilacs

The white haze on Lilac leaves is powdery mildew

By: Sandy Feather ©2013
Penn State Extension


Q. We moved into our house three years ago. The property has a row of lilacs across the back that I just love. But every summer, the leaves get this white film on them and they start to look pretty bad. Is this some kind of blight, and can I do anything about it?

A. Common lilac (Syringa vulgaris) is very susceptible to a fungal disease called powdery mildew. It generally appears mid-to-late summer as white, powdery patches on the leaves of susceptible plants. Infected leaves may be stunted, turn yellow, curl and drop prematurely. The good news is that powdery mildew is more of an aesthetic problem than anything truly damaging to your lilacs. 


powdery mildew
Powdery Mildew on a Dahlia

Powdery mildew is favored by high humidity at night because it creates a favorable environment for spore formation, and low humidity during the day, which allows those spores to be blown from host to host. Temperatures between 70 and 80 degrees are ideal for disease development.

 


Cultural Controls

Cultural controls include making sure lilacs are exposed to full sun and good air circulation. If the shrubs are planted too close together, you might consider removing every other one to allow good air circulation. Pruning the largest, oldest stems out at ground level reduces the overall size of lilacs and pushes a flush of young stems to sucker up from roots that will flower better and flower at a more appropriate height for cutting. Thin the young stems to the sturdiest, most vigorous ones and make sure they are spaced to allow air circulation in the center of the shrub. Rake up and destroy fallen leaves in fall to reduce the amount of spores overwintering near susceptible plants.


Watering Can Help!

There is evidence that powdery mildew is more common on drought-stressed lilacs, so providing supplemental water when the weather is hot and dry can be helpful. Fertilize very moderately, only based on soil test results. Fertilization pushes succulent growth that is more susceptible to infection.


Apply Fungicides?

Fungicide applications are rarely warranted since the disease is not life threatening.


Resistant Varieties of Lilac

Should you choose to plant lilacs in the future, consider planting resistant species such as dwarf Korean lilac (Syringa meyeri), Manchurian lilac (Syringa pubescens subsp. patula ‘Miss Kim’), and littleleaf lilac (Syringa pubescens subsp. microphylla).

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