In extreme heat like we have had, my iris do the same. Sometimes a whole leaf will turn brown. Just pull it off and discard. It's important to keep dead foliage pulled off bacause the narcissus fly lays her eggs in the foliage which then hatches into the iris borer. Iris borer hatches out and then tunnels into the rhisome and causes disgusting slimy soft rot. If this happens, apply Milky Spore, it destroys the hatching borers.

Nature Lover thank you. Where can I buy Milky Spore?

I order mine from Arbico.com but it is available thru Gardenres supply also. I like Arbico because they also have all kinds of organic natural controls for insect. Being an organic gardener as much as I can, I never use poisons to kill because it also does damage to the soil and streams. Arbico is in Tennessee.