Have you noticed your iris leaves getting brown at the top? It’s not so much the heat. It could be overcrowding, but it’s also a fungal problem.  If the whole plant is brown, dig it up and burn it or get it into a trash bag. Then spray the area with any of the fungicides (I don't know of any organic fungicides). Ambitious and ready to divide your irises? Make a solution of one part chlorine bleach to 10 parts water. That’s enough to kill the fungus. Soak the rhizomes (the underground stem) for ten minutes. Do not use bleach water on the soil — too much salt in it.

When your soil is cleaned up and loosened, replant your iris. The roots go 2 – 3” below the soil surface. You can put a little soil over the rhizome to prevent sun scorch or leave it exposed.

If the streak on the iris blade goes all the way to the rhizome, check inside the rhizome for mush or larvae. Clean it up or trash it. Cut back all iris leaves below the dried up part and spray with any of the fungicides. Repeat before or after rain or watering. The moisture enables the fungus to grow and you want to prevent its growth.

Most articles by professional growers recommend pulling off discolored or damaged leaves and throwing out seriously unhealthy plants. This prevents the disease from spreading.