My mother, when she transplants hers, dips them in a solution of 10 cups of water to 1 cup of bleach and then dries them thoroughly in air before planting them again. The bleach/water mixture kills any spores or bugs that are on the rhizome/bulb of the iris. I am transplanting mine in the fall, hoping for cooler weather, when hubby will have time to help me till up a big space where they can take over the entire area.