Lilac Question-White powdery substance. - Ask Extension
We have a client who has four lilac bushes on his patio that have a white powdery substance on them. He would like to know what it is and if he needs...
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Lilac Question-White powdery substance. #591519
Asked August 23, 2019, 1:15 PM EDT
We have a client who has four lilac bushes on his patio that have a white powdery substance on them. He would like to know what it is and if he needs to treat it. If so, with what?
Thank you,
Melissa Franklin
MSU Extension-Van Buren
Van Buren County Michigan
Expert Response
Your lilac has a common fungal disease called powdery mildew. Typically, the fungus appears as a white to grayish powder on the upper surface of the leaf. Powdery mildew is pretty much harmless to lilacs, especially when it appears at the
end of the season, which is usually the case. It doesn’t weaken the
shrubs in any substantial way nor does it keep the plants from blooming
normally the following year.
You don’t really have to treat powdery mildew on lilac, given its minimal effect on its host. At most, you could try to prevent it with the following actions:
Choose a less susceptible variety. Powdery mildew is pretty much limited to the common lilac, also called French lilac (Syringa vulgaris). Most other commonly grown lilacs, such as S. meyeri, S. patula and S. x prestoniae, are rarely affected or, if they do catch it, the damage is extremely limited and scarcely noticeable. But not all common lilacs are sensitive to powdery mildew
Give the shrub the best possible conditions, including full sun with plenty of space, good air circulation and well-drained soil, if possible slightly alkaline.
Prune the shrub to improve air circulation.
Water the soil at the base of the lilac during drought, because powdery mildew tends to settle on plants stressed by a lack of water.
Spray the foliage weekly with plain water during
hot, humid weather (when the disease usually starts), as this tends to
wash the spores off the leaves before they start to germinate. Do this
in the morning so that the foliage has time to dry out before dark,
otherwise it can leave the shrub susceptible to other diseases.
Avoid fertilizing lilacs, especially with lawn
fertilizers, as nitrogen, especially, tends to stimulate fast but
disease-sensitive growth. In any case, the lilacs are very comfortable
with very ordinary soil fertility: they’re just not heavy feeders.
Sanitation and good cultural practices are important components of
managing powdery mildew, especially late in the season. Rake up and
discard infected leaves to reduce the amount of inoculum overwintering
on leaf litter. Although rain inhibits spore germination, high humidity
and dew tend to make the disease more severe. Watering should be done
early in the day so plants can dry before nightfall. Plants that are
overcrowded or in shaded areas may be more prone to mildew. Rain
inhibits spore germination, but high humidity and dew may make the
disease more severe.
See the information in the link below.
