Bore control can be quite a task, sometimes, and, can be quite expensive, too ! I have used Beneficial nematodes before, and couldn't afford it !
! We did use them again, this season, as we found a place that is more economical:
https://biologicco.com/product...
A lot depends on "how many iris you grow", "how much time you have to invest", and, "how much money you want to spend", and , of course, if you are trying to be "organic". I have used both the nematodes, and bacillius thuricide (BT), in the beds bordering the veggie gardens and under the fruit trees (I will say that I have found "borers" in both these situations), and "chemical" control in the other beds (*Bayer long season grub Control...in the liquid form). The "regular "iris get two applications per season, and the rebloomers get one application. (in the last 4-5 years, I *think* I remember finding several cases of "borer sign", but no borers) The best thing that you can do for borers, IMHO, it to maintain clean beds, and, if possible in your area, to "burn over" the beds in the late fall.