It is just iris leaf spot. Very ugly, but doesn't cause serious damage and May go away the next year, or not. I have heard from horticulture sources that there is one specific funguside that actually works in advance (Chlorothalonil which is in Daconil; others say any will work if multiple treatments used; irisgal says it just depends on the year. It certainly helps to clean up all the crud between plants and cut the bad leaves off.

Thanks. Mine have been doing this for 2-3 years now but I haven't been able treat it because of having a baby then my health. Then once I could things I was told to use by local nurseries in case it was borers were either all banned or not safe with kids and pets around. My dog was dumb enough to eat slug bait, etc so I always had to be really careful what I used. (Since passed. She was nearly 16.) I suspect overcrowding is at fault as well.

I cut the bad leaves off every year as well.

This is the unsightly time of year for iris foliage. The outer leaves of each fan are slowly yellowing and dying. Part of the process.

I think this year my iris were entirely leaf spot free!! I've never seen rhyme or reason to this.