At our local meetings of the iris society they mention that you should use bleach without the additive that makes it "splashless" when you soak your rhizomes.
Good luck. I had a lot of trouble in one area of my iris bed last season due to heavy rains. I amended the soil in the bed, trying to improve the drainage. Ironically, rhizomes of the same varieties flourished on a neglected, rocky hillside with poor clay soil, where they had pretty much been tossed.
