my SIL has some peonies with black spots on the leaves, any one know what it could be and could it effect blooming, these 2 plants have failed to produce blooms the past 2 years

Could it be aphids? I really don't have a clue that is just a guess. Hope someone is able to help you. If you can you should post a close up picture so that we can see it good.

My peonies have come & gone already. Did you have a very wet spring. Too much water & humidity can cause a fungal problem. Flowers may still bloom. I have a habit of picking off leaves that have disease as I think of them as cancer that may spread.

Here is a link to a peony publication put out by Kansas State University. There is information in there about diseases and what to do. In fact there is about anything you ever wanted to know about peonies there...

http://www.ksre.ksu.edu/library/hort2/mf1083.pdf

Great article. Thank You!

Your welcome, and good luck. I love peonies.

it is probably a fungal infection known as black spot. Roses get it too, usually when it is very rainy and humid. Go to your local nursery and ask about what to treat them with. Your sister should pull off the affected leaves and get rid of them. I will look to see if i have some of the stuff i treated my roses wsith last year and if i find it will let you know.