Diablo Ninebark...Mold? Mildew?

gazania_gwAugust 25, 2007

This photo is of my Diablo that is less than it should be. When I tagged the shrub 4 years ago at the nursery it was full, and very healthy. It was delivered to me a week later along with a couple trees and several other shrubs I tagged the same day. When I planted the Diablo, I noticed one small branch had several leaves that had turned nearly white. It has declined a little more each year till now it is pretty sad looking. Whole branches have died back as the mold/mildew progresses. It is planted in a south east corner where the house wall meets an east facing porch. It gets about 6 hours of sun daily and air flow seems pretty good there, but this problem seems to be getting worse every day. Ninebarks are reputed to be nearly trouble free, so I am surprised by the problems with this one. I have another Diablo planted along the south side of the house that this year for the first in it's 7 years has a very few such moldy looking leaves in the interior of the shrub where sun and air would be at a minimum, but is otherwise a beautiful specimen. Anyone else experienced problems like this with their Diablo?

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After posting the above, I did a web search on the subject and came up with the following paragraph in a Nursery and Landscape Report out of Ontario. When I did a search last summer, I came up with very little, but now there seems to be a lot of talk on Ninebark and powdery mildew. Too bad. Sounds like a lot of effort must be put into controlling it.

Look for thick, white, powdery fungal growth on the newest leaves of Physocarpus opulifolius (especially Diablo). This is powdery mildew (likely Sphaerotheca sp.) that has been reported widely on our ornamental ninebark. This fungus sporulates quite profusely on Physocarpus and is difficult to control with fungicides once heavy sporulation is evident. Remove and destroy infested tips and continue to do so throughout the growing season while protecting new shoots with fungicides (where necessary).

Here is a link that might be useful: The report

    Bookmark   August 25, 2007 at 2:53PM
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I know that with perennials, drought-stressed plants are much more likely to develop powdery mildew, and I wonder if this is true of ninebarks as well. It seems counter-intuitive that dry conditions lead to more mildew, but it's apparently true.

    Bookmark   August 26, 2007 at 3:50PM
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"It seems counter-intuitive that dry conditions lead to more mildew, but it's apparently true"

Powdery Mildew does not really need moisture on the leaves to get estabished, it prefers dry leaves. The rain/irrigation wash the spores off the leaves...but high humidity it LOVES!!!!

    Bookmark   August 28, 2007 at 9:48PM
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No mold or mildew, but I am concerned my diablo may be sick.

I cut away a large dead branch a week ago. Now today I noticed a couple more dead.

I hope this isn't signs of a dying bush? It's 3 years old and has been doing fine. Bloomed beautifully last spring.


    Bookmark   September 1, 2007 at 10:06PM
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