It's hard to treat something if you don't know what it is. If the plant is stressed from whatever this is, digging it and messing around with ajax is only going to add more stress to the plant, any bleach based treatment is useful only if you're combating a bacterial rot issue.. This doesn't look like any bacterial kind of thing to me. If this is a rare and hard to find cultivar, it's worth trying a few of the suggested treatments like removing the needles which will add acid to the soil as they decompose. In the bed where my soil was too acid, many of the irses just didn't thrive, and just died out, I never saw anything like this from that condition. I did have a few varieties that did well in the acid soil though most did not. I called it the bed of death. Now that I've added a bit of garden lime to the soil and got the PH up, it's doing well. If the plant is one that you can replace easily, you might consider tossing it and getting a new one. I wouldn't plant another iris in that spot for a long time. Is there a lab somewhere nearby that you could send a sample to and have it analyzed? Could this be a result of the very high temperatures in your area? If you remove the affected leaves do the new ones still have this condition? There's just so many things it could be, yet not like anything I have seen before. Good luck with solving your mystery.
