I also just found this advise in another person's thread and wanted to copy & paste it here so I could find it again - "Tom's advise (If you are not averse to using chemicals, you can treat your iris beds in the early spring with Bayer Grub killer, the stuff that's made for lawns) is great advise.
I've been using the Bayer Grub killer for years now. I make sure I apply it before the temperature reaches 70 degrees. That's when the little buggers hatch.
The best way for me to look for borer damage is to pay CLOSE attention to the "center" leaves on the iris fan."
