I have a peony with a white coating all over its leaves. It’s as if it were a mold, but it sits out directly in the sun. What is it and what can I do for it?
The Gardener’s Answer
It sounds like your peony has powdery mildew. This fungus is more prevalent when the weather conditions are right. Humid, warm days followed by cool nights are ideal conditions for these spores to spread. Like all other ornamental plants, peonies are more susceptible to powdery mildew if they are watered overhead, over-fertilized, and/or do not have sufficient air circulation.
The good news is this fungus will not harm your peony. Aesthetically, it looks bad, but it will not have any negative effect on the overall health of your plant. These spores can over-winter in the surrounding soil or mulch so it is important to remove all infected foliage. As a preventive measure, a registered fungicide can be applied at the first sign of this fungus. Horticultural and neem oil can be effective in mild cases after the fungus is present. Always follow product application rates when using controls. If your peony is unsightly, it is best to remove and discard all infected foliage. It’s also a good idea to disinfect your cutting tools to prevent disease spread. I hope you got to enjoy the blooms before the fungus appeared!