disclaimer: this is a recommendation for research only
...... make your own decision to use based on your findings.
while manual efforts to control grass growing in small (er) iris plantings are definitely an option, That method becomes impossible for those of us who have extensive iris collections or commercial sized plantings and need to save time and effort.
I recommend that those forum members who DO have large iris collections do research on a product called Sethoxydim. This is a selective herbicide that is the active ingredient in a number of consumer level products. This is an effective remedy for controlling grassy weeds in a number of ornamental species plant bed issues, not just irises.
I use a professional level product containing this ingredient and i've achieved good control over grassy weed invasions in my iris field. I use this as a last resort, tho and only in areas that are heavily infested. I follow the label guidelines strictly and some iris varieties may exhibit some temporary yellowing and stunting of the foliage after application of the product, but that has been rarely observed by myself.
Use of a adjuvant (spreader/sticker) overcomes the wet foliage issue and improves the product performance.
I've used products containing Sethoxydim since it was approved in 1995 with good results
