Powdery Mildew on Peonies Can Ruin Blooms – Here's How to Identify This Common Disease and Stop It Fast

Are your peony leaves turning white? It's likely due to powdery mildew. Powdery mildew can affect many plants, including peonies. It's a very common fungal disease that doesn't usually kill plants, but can weaken them and diminish blooming.

Powdery mildew can also make your plants more susceptible to pests or other common peony diseases. It can disfigure peonies' beautiful blooms, which are a highlight of the late spring to early summer garden.

Learning the causes of powdery mildew on peonies and how to prevent this common problem is your best defense. I'll walk you through how to keep peonies healthy and fight off fungal diseases before they get out of control.

How to Identify Powdery Mildew on Peonies

So what does a peony with powdery mildew look like? You can identify powdery mildew on peonies by the white spots that appear on your plants. It almost looks like your peony is dusted in flour.

This white growth that forms on peony plant leaves is powdery mildew. Occasionally, powdery mildew appears on the flowers as well. Any new growth may also appear powdery, exhibiting a stunted or distorted appearance.

In addition to the powdery growth, infected leaves may drop from the plant. Flowers can also become distorted and unattractive if your peony has a severe case of powdery mildew.

What Causes Powdery Mildew on Peonies?

Powdery mildew is a fungal disease in peonies. There are actually many types of powdery mildew, all with varying growth requirements. Powdery mildew fungi can germinate either with or without water. However, humid conditions are quite common for growth.

That's why it's best not to overhead water your peony plants, unless you do it first thing in the morning. This allows foliage to dry in the sun. If you overhead water late in the day, leaves may stay wet all night, which creates a breeding ground from fungi and other issues. However, you can't control water from rainfall so powdery mildew may take hold during wetter growing seasons regardless of how you water peony plants.

Other ideal conditions for powdery mildew are moderate temperatures, shade, and areas with poor airflow, all of which which generally spawn moisture. Lots of heat and sunlight will hinder the development of powdery mildew. Good airflow is also essential for preventing powdery mildew on peonies. Don't overcrowd your plants or else you risk diseases developing and spreading fast.

How to Treat Powdery Mildew on Peonies

Once powdery mildew appears, it can be difficult to treat, depending on the type it is and how severe the problem is. For this reason, prevention is key. Avoiding susceptible types of peonies, locating peonies in full sun, providing suitable air circulation, and practicing proper peony care is usually adequate. Watering in the morning hours may also help.

However, even when taking the most careful precautions, powdery mildew may still strike. Although fungicides, like this copper fungicide from Bonide, can help when applied early in spring as shoots first emerge, heavier infections may require horticultural oil or neem oil.

You can also create a homemade solution for powdery mildew. Mix together a tablespoon (15 mL) each of baking soda, horticultural oil (or canola oil), and liquid dish soap (without bleach) with a gallon (4 L) of water.

Then use a spray bottle, like one of these from Amazon, to apply the solution to your peonies every 10 to 14 days throughout the spring and summer months. Do not spray the solution during hot and sunny days and always test on a small part of the plant first before using it on the whole plant.