From my iris days, it was always recommended to carry a container of 10 to 20% bleach solution to dip any trimming tool into before using the tool on another plant to prevent spreading diseases. Burn any discarded diseased plant. Avoid planting another plant in the same hole or area where a diseased plant was removed due to the soil being likely to harbor the disease. Sanitation was very important with iris and roses but peonies were never mentioned.
