Bought a hydrangea very cheap this summer ... Cheap because is has rust spots and was past bloom. I wonder if I plant it now, would it likely be effective if it treat the disease in spring.

Same story with some peonies. They bloom pretty well by get bad black spots later in the season. I wonder if I transplant now, again, should I treat in spring? Should I have concern that they will survive due to the disease? Give.

Should I cut most or all the plant off of either of these when I transplant them?