Hello Connie,

Sorry about your peonies!  I do not believe they have a disease, but rather a condition known as chlorosis.  Chlorosis is a condition where the plant is not able to take up enough chlorophyll.  This can be caused by poor drainage, compacted or damaged roots, high alkalinity or nutrient deficiency.   If your soil is too rich it may affect the plants ability to absorb certain nutrients.  

If it is a nutrient deficiency, the most common would be low iron, manganese or zinc.  In which case, spraying or feeding the plant with these minerals would improve the situation.  However, the only way to know for sure is to get a soil test, which is offered by MSU. I have attached a link that provides the information to get you started with the process.  Once you know the results, you can be more accurate with your plan of attack!  

https://homesoiltest.msu.edu/get-started

All the best, 

Kathleen