I have a white powdery substance on my peony leaves. What to I do to rid them...

Asked June 29, 2015, 5:56 PM EDT

I have a white powdery substance on my peony leaves. What to I do to rid them of this? I was told last year to use Captan.

Burlington County New Jersey

1 Response

That is powdery mildew. This has become a bigger problem on peonies the past few years--possibly a new varient of the old powdery mildew--even on plants that had no problems for many years.

You can spray with a fungicide labeled for powdery mildew. Fungicides are preventative--not curative. They will halt further infection, but cannot restore infected leaves to health.

To handle this next year, cut down all infected foliage this fall as soon as frost turns it brown (or before if the mildew has killed it.) Get rid of this infectious material. New spring, keep an eagle eye on your peonies, and as soon as you see one infected leaf, pull it off and spray all the rest of the foliage with a fungicide. If you have a good sense of when the infection will start each spring, you can just spray before any symptoms show up.

Here is our website info on powdery mildew: http://extension.umd.edu/hgic/powdery-mildew-annuals-bulbs-groundcover-perennials-and-vines

ECN