Our plant pathologist says it's hard to tell if the symptoms are viral, but that viral infections on peony don't usually cause the plant to die out. (That said, it can be contagious, and it can't be cured.) The third photo definitely looks more like a nutritional issue (like a deficiency, maybe in iron, manganese, or magnesium), but the other two images are harder to diagnose. We can't rule out a minor nutrient issue. A laboratory soil test is the only way to accurately measure the current nutrient content (save for nitrogen levels, which isn't tested for since it fluctuates naturally too much) to determine if supplementation with fertilizer would be beneficial.

Virus symptoms often worsen and become more prominent over time, so you could wait and monitor the plant this season to see if the yellowing develops a distinct pattern or becomes more extensive, or if it fades away. Sometimes viral symptoms do fade on their own, like during certain weather conditions (say, summer heat), but if a plant were infected, they would probably regain some symptomatic foliage at some point the following year. Short of laboratory testing kits for certain viruses, which can be expensive, there really isn't a way to be sure unless the symptoms become much more distinctive. (Even then, it's hard to know which exact virus is responsible, not that it would really matter at that point.)

Miri

These symptoms might be viral, but it's hard to say with certainty. Viral infections tend to develop worsening symptoms as the disease progresses, though on occasion (like with some viral diseases of Spicebush) the symptoms actually recede over time, perhaps due to heat or changing environmental conditions. Therefore, time may tell if the plant's appearance worsens or remains stable. Due to attending a conference, our plant pathologist is unavailable for consultation for a couple days, so we can seek his feedback, but it might be a few days until we can respond with his assessment.

Miri

Thank you for your patience. Our plant pathologist was able to look at the new photo and, in combination with the older photos for context, is more convinced that this suggests a viral infection. We can't be certain -- only a positive virus lab test would be confirmation -- but it is suspicious, and he notes that peonies are not-infrequently infected with viruses.

Miri

Thank you so much. I got my soil tests back for the peony planted area, and it says it's low in phosphorus, so I will be amending with 0-46-0 as recommended by the Del extension office soil testing facility. I suppose it sounds like I may still want to consider pulling this one for viral infection though, given the pathologist's assessment of the likelihood that the symptoms are viral? Really appreciate the guidance I've gotten and am glad to have your team to query.

You're welcome.
Yes, viral infections, if present, are incurable and have the potential to worsen over time, which is why plant removal is one of the recommended actions when a plant has a suspected virus. As we mentioned earlier, time may tell if the plant's appearance worsens or remains stable in this case, so you can keep it for a while longer if you want to see what happens, but that may risk spreading a virus into other nearby peonies.

Miri