I would agree on suggestion to lift the iris and see what's going on there. Most likely it's just not draining well. Or rather, not draining to its liking. 1) Cut the flower stem. At this point since not a single one opens it's rather like a festering wound for iris. If it feels better later it will give you a new bloom stem. I have counted at least 6 new growth spots. Some are very fresh . So you have 5 more stems left for this year if plants recovers. 2) After examining roots on rot you can return plant back, but consider adding some spent soil inter it or mix in a bit of sand/silt if it needs drainage.I happened to have a variety or irises in my garden and so far only some of the Japanese irises need watering. All Siberica and Germanica grow in soil that is very high on sand particles and seems to be doing great when baked. I watered them only once this year during a bit of a hot spell earlier in May.Here's what soil looks like: As you can see, it's really poor and dry. But that's what they need. Pretty much same conditions as lavenders like. On your photo soil looks pretty dark, which means either that area gets watered a lot or it has too much organic matter for iris specifically. So moving and dividing sounds more and more reliable solution. I've divided some of mine this year down to 3-4 centimeter. You may try do do few similar rhizome cuts to try different parts of your garden.If the soil is right, you should be getting about this much growth : (these were potted around February inside on a window after being divided and put in a ground around end of March )If you have iris in that spot because companion plants cover it when it's out of season, may i recommend different companions? Maybe lupines. They fill up nicely and about time when irises are about to go away. Hope your iris survives!