Could it be grey mold? Has it been wet and rainy? Google gray mold and see what you can find out.

I thought maybe gray mold/botrytis, but our spring has been pretty dry actually. The peony gets good air circulation, even though I put leaves around the base in the fall (always have), and remove them early in the spring. The growth that is coming out looks great--looks like it should/normally does. I'm just at a loss--literally the whole 2/3rds of the top of the plant seems dead. Any other ideas? Thanks!

Look for holes along the stems. Early for them but sometimes insects will bore into the stems causing damage. It does sound more like a fungus that insect damage. If no holes found send an email to Rick Rogers of Brothers Tree Peonies to see what he suggests.

Here is a link that might be useful: Brothers

Thanks for the suggestions. I wanted to post a followup in case anyone else has this problem. I did contact Rick, and he was really helpful. Sounds as if our freeze-thaw cycle this spring may have killed the buds on the upper part of the plant.

Rick is great with answers. Even better if he does not know he will tell you that he does not know something.

Rick really is helpful. To followup again, I did some hard pruning yesterday and discovered some kind of borers and larvae! Makes me really angry. So, I'll be applying systemic and hope that it comes back. My poor peony--it was so gorgeous.

If nothing else it should send some shoots up from the bottom. Just make certain that they are similar to the tp foliage.