... browning tips are a signal that an otherwise healthy iris plant is re-allocating resources down to its lower bases and rhizomes. Also the iris is developing new anchor roots that will take over the nutrient and water support for the new fans. Once these are fully developed to start the process, the browning and leaf fading should ease a bit. This is a natural occurrence at this time of the year.
The degree of brown tipping can vary from variety to variety -- I have a healthy clump of "Cool Charlotte -- Blyth '12" that looks like its moisture starved, but such isn't the case. If the brown tips start progressing down the leaf or take on a decided reddish hue with a yellow border, then other issues are at work. But just browning on the tips isn't anything to worry about.
Sun scorch problems will manifest themselves on the sunward side of the leaf fan but the shadowed side will be a regular green.
Also as the iris clump continues to re-direct the starches and sugars down towards the rhizome at this time of the year, outer leaf fans will be sloughed off (turn brown/tan) to prioritize energy towards the center of the fan where the plant metabolic activity is still taking place and active rhizome development is going on.
