I agree, too. Your iris actually go dormant for a time, a few weeks after they've finished blooming. That would be an excellent time to just dig up the whole area, pick out the monkey grass, and plant your iris back where they were. Try not to let the iris roots dry out as you are weeding. Maybe do a small section at a time, so the iris plants aren't out of the ground for too long. Or keep an old, wet towel near where you're working, and wrap the iris roots in that while they're waiting to go back where they belong.