They are common anywhere east of the Mississippi I am told. I have found that if you cut off all the leaves to leave just 2 or 3 inch stubs and burn (or send to the landfill) the cut leaves each fall, it helps a lot, as that will get rid of a lot of the eggs, which are laid on the leaves and nearby debris in late summer or early fall. Then I rake up any debris and remulch for the winter with some clean mulch. In early spring about the time crocuses are blossoming, after raking away and discarding the mulch, spray (or dust)the short foliage with insecticide. Cygon used to be recommended, but has been discontinued. I have been using malathion in recent years. You are supposed to spray them every 10-14 days till about late June, although I usually only get around to it once or twice, which seems to suffice. Once the borers are down into the stems and rhizomes, spraying won't do any good. I have also been using a systemic rose fertilizer on mine. I don't know if it is helping, but I haven't had much trouble with borers since trying these measures. Otherwise, the borers will chew up your bed till all you get are little scrawny leaves, but no blossoms. Before I realized my problem was from borers, I had decided to dig up and move my irises to a fresh area, thinking the soil was depleted. All I found were little one-inch pieces of rhizomes, not even enough to dig up! Since the borers are actually larvae of moths, keep removing the leaves every fall and spraying at least in early spring as a preventive measure, as the borers will keep attacking year after year from outside of your garden. Some literature suggests squishing the borers inside the iris leaves, but I have never been able to figure out where they were. Take heart, they are controlable, just a nuisance to deal with. Don't give up on such a lovely flower! Northwoodswis

I have iris borers every year. I did a search to see what growers reommended. The consensus was Cygon or Malathion. I did read on one site (Trails End I think) that some growers are experimenting with dormant oil. I had wondered myself if this would work. I'm going to give it a try this spring. Can't hurt. Marg

Thanks v. much for your replies. I'm not even sure if the borer is winter hardy here. I'm nearly sure I had them last summer but I did order new irises from out east so they may have been a one-summer event.

I will cut and burn all the foliage (yikes I have a lot of irises...) this spring, and try two sprays of Malathion. As mentioned we can't get cygon anymore.