Rotting Rhizomes; how to treat soil before re-planting new

I have two small Iris areas separated by a wide stone walk. the beds are on a hill in terraced beds, so there is usually good drainage. Nevertheless, I had one side of the walk which did beautifully & one side where more than half the rhizomes were rotted. Some appeared to have holes in them, so could that be iris borer? What other factors besides drainage could be causing this? Also, what do I need to do to prepare the soil to keep out borers, etc., if they are the cause? In my other house, I had older Irises which were totally reliable. Now that I'm trying to start new ones, I realize how complex they are. Many thanks, Cubbydoodle

check for borers and if you have them run do not walk and get Merit.

D

I know Merit is supposed to be used very early, but can it be used now also? Yesterday I found a small "unmerited" patch that has some borer babies in it. Do you know if soaking in bleach will kill the borer babies if I dig up all the rhizomes that may be infected, soak and replant?

Yes, you can, make sure you cut the rot off first, give a bleach and water bath, then let it dry out for a few days, then replant.