Hi Patti, thanks for the question.

The rhizomes (underground stems) and the "clasping auricles" (see links below) suggest that this is the infamous quack grass which is very difficult to eliminate from the landscape.  Sethoxydim is active ingredient in post-emergent weedkillers that specifically targets grasses. Iris is listed as tolerant of some of these products. It is safe for irises when used as directed. Apply it directly to the quackgrass, avoiding contact with your irises.

Glyphosate, a non-selective herbicide that can, kill most quackgrass rhizomes; however, it can also harm irises if it comes into contact with them. Painting the herbicide onto the grass leaves rather than spraying will help prevent contact with the irises. 

Be sure to read and follow the label.  The label is the law.

Quackgrass | Cornell Weed Identification

C 867-8_4.PDF (uga.edu)

Weed Control in Iris | UGA Cooperative Extension

I hope this is helpful.