I may be wrong but I think most of the energy to the rhizome is supplied by the fans of the iris plant via photosynthesis, rather than by stalk. The stalk incidentally is attached to the "mother" rhizome which will eventually die off after blooming.
The iris borer climbs up in the blades of the fan early Spring, chews its way in and then travels back down to the rhizome. If you did have iris borers, then by the time you cut down the stalks, it won't make any difference. Also, apparently the iris borer is not commonly found west of the Mississippi River.
However, having said all this, I have found critters that look like iris borers eating their way through in rhizomes. But upon closer examination, they appear to be something else. Has anyone else seen this as well?
