Theoretically, if I move the orphans I was able to save from my borer plague to a new area and make a cheesecloth or netting tent over them before the borer moths hatch, would it protect them this fall?
I tried the borer squish technique this spring, but when I went down the leaf there was just thick goo and I couldn't see any borers. Eventually, however I did find some still in the leaf. I assume this is what my plague of rot is this year.

I plan to start a new nursery bed with gravel mulch and plant rhizomes of favorite irises as well as rescued orphans to keep them safe for this year while I sort out the big patch. That's why I will try the netting or cheesecloth covering, so any flying moths won't lay eggs on them. How tiny would the holes need to be? Do you think ordinary netting from the fabric store would work?

Well, I suppose a "tent" would keep things out....but if you "Transplant" a borer...or eggs...into the bed, along with the irises . And , IMHO, that would be a real easy thing to do, as the eggs,...as well as small adults...are pretty easy to overlook ! Maybe , ...if you are "anti chemical"...you could invest in some nematodes, to treat the "new" bed ? And, if you aren't "anti-chemical"....just treat with IT, and do the existing beds, as well

Aren't nematodes prohibitively expensive? And what is IT?

"IT" would be the "chemical", and expensive is a "relative term". I used the "scanmask" sprayable, from here:
https://biologicco.com/product...

and . IF they last as long as they say (before retreatment is needed...18 months) it will actually be cheaper than the *Bayer grub control and the other stuff I use, now . Some folks have real good luck with nematodes, but, it remains to be seen whether they will work out for me.

Thanks for that link, Arlyn. I don't have iris borers, but I do have thrips aplenty.

How many of you in borer territory use merit and how many are able to control the pest without chemicals?

I use Bayer's grub control in the spring after the new leaves start to grow.

This is offered only from my personal experiences. I am sure sure there are plenty of "borer experiences" out there. This is not an endorsement or recommendation of any commercial product. At one time Ortho offered a product known as a "systemic insect killer". That was several years ago; and I think the EPA has (had) ruled against it. It is no longer available that I am aware because of safety concerns. Long story short; Bonide had a product last year which was available. Now Bayer has the granular form available which I have (and still do) use. This has been mentioned in Tom's post above. It sure helps me.

Borer control is an ongoing fight for iris growers in the eastern U. S. & Canada. The last time I checked borers are not found in the western states. No matter what is used I highly advise reading the directions for use; especially the fine print which I can barely read. Safety in using insecticides is critical. Here is something I wrote back a few years ago. It might be useful to someone out there. https://garden.org/ideas/view/...

Some product pictures that I (previously) or still use.

Ughh! Those borer images! Ughh!

(Am I a bad person to be happy that I don't have them here?)

Marilyn, You are fortunate not to have them. I am "bad" when I find one.

Just to add to the disgust for those enjoying borer pics:

What was found when rhizome dug

The critter removed, but before meeting his/her fate. (No pics of the 'after' results.)

After cleaning, letting area scab over and planting. It grew well the next season.

All of this is too much work if you have lots of them, so prevention is best.

I am strongly leaning toward resuming use of bayer merit next spring on anything that may be left after this year. I am seeing notched and badly rotted leaves and have been cutting out each rhizome connected to it. Curiously, I am not finding any borer tunnels in the rhizomes. Nor am I seeing any of the sawdust like frass on the ground. Maybe it is too early for that because of our late spring?

I think most are probably still in the leaves ,

Is there any advantage to just cutting off the rotted leaves and leaving the rhizome if it hasn't tunneled yet?

Good way to go, just take off the bad foliage and trash it. Check the rhizome where the leaves came off and cut back any soft areas allowing the cut to sun/air dry. No need to even take the clump out of the ground. Sometimes foliage or stalks get mushy and rhizome is not affected. Many can be saved.

Will the rhizome sprout new foliage if you leave it?

Yes

Thanks to everyone for all this info

I have used the Bonide product in the picture and also the Bayer Two-in-One granules for several years now. This year I did not have many borers except where the drench or granules did not land. The trouble with those products is that they only last for about 6-8 weeks so you must reapply.
The moths are not high flyers so tend to swing off of bushes or nearby foliage (in my case, my clematis) to get to the irises to lay eggs.
And YES, they are so gross and very hard to squish!!