You need to get them in the spring before they hatch. I use a systemic which the iris plant takes up. If there is enough in the plant, the borer will not live long. If you miss an area or do not put enough down (or are late in application) then the buggers have a good chance to kick ass. Even though I seem to be reporting lots of damage from them, I feel that I am having a very minor out break and that my issue is a spotty application (especially based on the concentrations and abrupt change over to rhizomes with no problems).
