cause.. too much water..

Hey Grizfan
I'm assuming from your name that you're from the Missoula area?
I think you've had even more moisture this spring than we have (Helena/Bozeman area). And I'm having the same problem...
Although, I'm having a great bloom year too! Iris that have never bloomed for me are blooming their hearts out. I'm losing half clumps and entire clumps to rot. I don't think it's all the moisture per say, but our irradic temperatures to go along with that moisture. I don't know about you, but we had a semi hard frost the beginning of this month. That can really stress the iris!
I'm probably not doing the brightest thing in the world, but I'm waiting and seeing what my clumps will do. Often times I'll have little ones sprout from a clump that I thought had totally rotted. I've tried lifting the entire clump, seperating it, soaking it in a mild sollution of bleach water, cutting out all rotted areas if there's solid rhyzome, letting them dry in a cool (out of direct light) area, then replanting only to have them begin to grow leaves and then begin to rot again. You may have better luck than I have with that method...
I'm sure you'll get some detailed answers here as the people who've been here awhile really know their stuff.
Good Luck!
Heidi