Certified GKH Gardening Expert
The best recourse is hand pulling along with some preemergent herbicides. But the bed needs to be weed free before using those. For grassy weeds, there are products that will kill grass but not ornamentals. But none of the products will eradicate all weeds.
You can lightly mulch your iris beds, but be careful not to get too close to the rhizomes or rot could set in.
If you get real desperate, you can always start a new iris bed, or remove all irises from existing bed, spray with a non-selective herbicide, wait recommended number of days to plant, then move all your irises back.
If you are very careful, you can "paint" an herbicide containing glyphosate on the weeds with a paintbrush.
Here is an extension publication that lists all the possibilities: