According to the Penn State Extension Office: "Do not plant infected rhizomes. Destroy infected plants." It would be best to reach out to your local cooperataive extension office or a local nursery who have experience with Iris diseases and a treatment regimen. We do carry a product called OHP Strike Plus 50 WDG Fungicide that's labeled to treat for Botrytis as well as Cleary 3336F Fungicide.
We apologize, but OHP Strike Plus 50 WDG Fungicide is not available in any other sizes. Please be advised that this product has been discontinued. We would recommend getting an identification of the disease you need to treat so that you can be sure you are choosing the correct product for your needs.