Well -- when we found a borer infestation (many years ago in Chicago) -- we dug up every Iris and soaked them in bleach water. Then we pared away any damaged flesh of the rhizome -- and replanted them. If I were doing it now, I would sprinkle Comet cleanser on the raw rhizome tissue before replanting.
There may be an easier way to do this -- if so, I hope someone else speaks up. How many Irises are in that bed?
