Fortunately, we do not have Iris borers in the western United States. However, the Iris borer can pose a very difficult problem in the Midwest and along the east coast. They hatch in the spring and chew into the leaves, leaving chew marks on the margins of the leaves. They then bore down through the leaf, leaving long wet looking streaks on the leaves. Once they get into the rhizomes, they gorge themselves. What they don't eat then can rot.
First, always maintain a clean garden. If you see the borers in the leaves, simply squash them. We recommend using the insecticide Cygon 2-E. Spray in two week intervals from about the time the tulips bloom through mid-summer. A 10% solution of Murphy's Oil Soap (one part soap for every nine parts water) can be used as an organic alternative to Cygon.