Looks more like powdery mildew, a fungus and a rather common fungus that can affect many different plants and often turns leaves gray, usually unsightly.  Some  plants get  it every  year and it becomes worse in humid weather,  especially  in crowded  plant  situations that restrict airflow.  Read more here;
https://www.canr.msu.edu/news/scouting_in_herbaceous_perennials_powdery_mildew

Understand that fungicides do not cure.  They do stop progression but do not cure.  To be effective, plants have to be sprayed before any sign of the disease,  or very  early when first seen to stop progression.  Not a thing you can do for it right now. Many plants are afflicted by various funguses and leaf spot funguses but the good news is that most come up just fine the following spring with no sign of any  disease.