The white areas are more prone to sun damage and don't last as long as the green areas. Nothing is wrong, just normal die back, a little quicker when it doesn't have it's chlorophyll protection. I see the same thing on my hostas that have white areas and get too much sun.

Mike

Thanks for your response Mike. It seems quite probable that that is the explanation but I am concerned they have not bloomed this year. They usually bloom in early to mid-June but nothing so far. All my other Irises (bearded tall, bearded dwarf, Siberian) have flowered and died, so is it possible that there is something else stressing the plants?

I am in zone 6 ish in central New Jersey and my pallida variegata blooms but only now and then. When I lived in West Va, zone 7, it increased and bloomed like you wouldn't believe but not here.
I think it may need less sun that the other irises but am not sure.
Marian

Hi Marian: Very iteresting information. Mine have bloomed every year but the first, but this has been a very different year for us. We are in a snow belt and usually very cold. But we had a very dry post December year. Parts of my property which are usually under water in the spring were dry this year. Then we had a very cold spring and now it's extremely hot and dry. So perhaps it's too much stress for them. They are in a full sun area next to a stone walkway, so they really get lots of heat. They look quite healthy though, so I'll just keep watching them carefully. Such beautiful blooms, though!! Thanks for the info.