Sounds like iris leaf spot fungus.

Spraying with a fungicide will innoculate clean leaf areas. Some years my iris have it badly, some not. Very unsightly but not fatal.

Oops, don't think it's called a fungus. Brain dead tonight.

It could be a fungus. I have been battling this on my iris' for a couple of years now. It is very unsightly. However, I have not lost any iris due to it yet. I'm not sure if my sub-zero winters are helping with that or not.

Here is what info I have found to try to get rid of it:
-clear all leaf debris on a regular basis. Especially in the spring and fall.
-clip leaves, removing spotted portion
-keep iris divided to provide good air circulation.
-avoid top watering (obviously rain is unavoidable, and this tends to spread the fungus when the rain splashes on the ground)
-spray a fungicide on all leaf surfaces, read bottle but generally this needs to be reapplied once a week. At least during the wettest times of the season. If you have a lot of ground to cover you might want to consider buying it concentrated and using a wand pump sprayer.
The fungus spreads when it rains or when watering with a sprinkler. I do notice that once we get into the hotter summer months, the spots definitely slow down.

I have a TON of iris, so this has been a tough battle for me. But I think I may have it licked it in my dwarf iris garden. However, I just noticed some spots on some of my tall bearded iris' some distance away.

I have also noticed that it does not effect the siberian iris' in my gardens.

I have what appears to be the same fungus you are talking about. It appears to be contained (now)to one plant. The plant "wine and roses" but the plant is also suffering from short stalks and when removing the stalk to have a 'look see' , I've found whitish looking tiny bugsplus it looks like sticky stuff inside leaf too.
Same thing? Or do I have something entirely different.