Was the infection powdery mildew or one of the leaf spot / blight diseases common to peony foliage? (Refer to the linked pages for images and more info. It is possible for them to get overlapping infections.) While some fungicide sprays can suppress these diseases to help prevent infection, they are not guaranteed to work, and such treatments often need to be repeated well into the growing season. For diseases that are largely cosmetic and not necessarily life-threatening to the plant, such treatments might not be worth the expense and effort, especially in years when rainfall interrupts the treatment schedule and allows infection to take place. Fungicides cannot cure any existing infections, though, so if applied too late, too sporadically, or if they just happen to not work well in a given year, they will be unable to reverse any existing damage.

We usually do not recommend fungicide use since it's not always reliable and its use might risk pollinator health or harming other organisms. If you try one, make sure the product label lists the targeted disease (powdery mildew, "blight," "leaf spot," or something more specific like Cladosporium) and follow its directions for use carefully.

Miri

Hello Yvette,

Thank you for the photos. The first picture shows classic leaf blotch symptoms and the second shows viral symptoms (the yellow rings are very characteristic). Not all plant viruses cause serious plant damage or death, but they are not curable. Do not use pruning tools on that plant without disinfecting them before using them on other plants, or contaminated sap might transmit the virus to them as well.

If leaf blotch and/or powdery mildew becomes excessive, you can trim the foliage off and dispose of it. Regrowth might emerge clean, at least for a while. If trying a fungicide, you might still be able to apply protective sprays (several will likely be needed) starting now (or soon) if you wanted.

Fertilizer is not a substitute for a plant having enough foliage (the nutrients would largely wind-up being used in the leaves anyway). Fertilizer is a bit like a multivitamin for plants, in the sense that it's not food (sunlight is their "food") but rather supplements nutrients not provided by the soil. Generally, established perennials do not need any fertilizer, or at least not regularly, and plants that are infected or battling a pest outbreak should not be fertilized until the problem is resolved (otherwise it might make the issue worse).

Miri