The leaves on my lilac are covered with a white substance. Is this a serious problem?


The leaves on my lilac are covered with a white substance. Is this a serious problem?


The white substance is likely powdery mildew.  Powdery mildew is a fungal disease.  It appears as a white, dusty growth on plant foliage.  In the home landscape, powdery mildew is commonly found on lilac, phlox, monarda, zinnia, and turfgrass.  Amongst lilacs, the common lilac (Syringa vulgaris) is highly susceptible to powdery mildew, while the Preston lilacs (Syringa x prestoniae) and dwarf Korean lilac (Syringa meyeri) are resistant. 

Powdery mildew is favored by high humidity, cool nights, and warm days.  Plants growing in partial to heavy shade are most susceptible to powdery mildew. 

Powdery mildew does not cause serious harm to lilacs.  The damage is mainly aesthetic.  Spraying with a fungicide is not warranted.  When planting lilacs, select a site that receives at least 6 hours of direct sun each day.  Powdery mildew will not be a serious problem in sunny areas.  Judicious pruning of nearby trees (to increase the amount of sunlight) should help reduce the severity of powdery mildew on lilacs growing in shady locations.  Another option would be to transplant the lilacs to a sunny site. 

Learn more about lilacs in this article: Growing Lilacs in the Home Garden


Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Horticulture and Home Pest News, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on . The information contained within may not be the most current and accurate depending on when it is accessed.