I had a nightmare with this last year and dug up every plant. All my beds were infested. I tried the bleach water, and all the plants I used bleach with recovered very slowly or did not thrive.
I tried plain water instead. Submerge the rhizome in a bucket of water for 30 min. The borers will leave the root looking for air. Drain the bucket onto hard pavement, a deck etc - then you can easily smash any still alive.
The iris wont suffer from the plain water and you need them to be clean of dirt anyway to look for holes. Discard or cut away parts of the rhizome with borer holes. They will just get infected with rot later on and you'll just be sad again.
Here's the bright side. I had huge clumps that only had a few tiny pieces unchewed. I replanted them with a heavy duty fertilizer 10-54-10. They are big and thriving this year. Some even bloomed this spring, other surely will next year.
This year I applied nematodes and there was only one small part of a bed where the plants looked funky. When I dug up the plants I couldn't find any worms, so maybe they got killed in progress. Some of those are sending up small increases and will probably make it. The nematodes seem good. I will keep using them for sure. And they don't harm the land.
MamaFan said: Yep. I've got em.
And it's not great.
I've thrown a lot away in dividing. I've got the healthy-seeming ones soaked in a bleach solution, as was mentioned. I've got more to check.
... Do what I gotta do.
And, that means a lot of extra dividing that I hadn't planned on doing. But, I'm on it.
I'm applying nematodes this year as well.
Fingers crossed.
