These bearded iris rhizomes have been stored in your refrigerator for TWO YEARS? And they're not all rotted mush already? Are they still firm and heavy, or are they dessicated and lightweight? If they are firm and heavy, I'm very surprised that they kept so well under those conditions. Refrigerator storage is staunchly warned against with bearded rhizomes because of the damp conditions.

In any event, if your rzs are still viable, a 20 min soak in a solution of 1 part bleach to 9 parts water is always a good idea. It won't necessarily prevent rot from occurring, but it will help eliminate chlorine-susceptible pathogens from the rzs before they are planted. Rinse the rzs thoroughly with plain water after the bleach soak.

I would think you are past your safe planting window for bearded irises in zone 6b. The rule of thumb is to plant at least 6 weeks before your first hard frost to give the plants adequate time to root in before winter.

Laurie