Signs of borers: edges of leaves chewed ragged, frass [light color droppings] near the base, fans falling over, hole in base of fans and of course in rhizome.
My treatment: similar to Arlyn's but without the chemicals, dig rhizome, trash any leaves with smelly rot on them, carve out the bad portion of the rhizome, let it dry and skin over, treat with bleach or bleach cleanser to reduce the chance of bacterial rot setting in. The rhizome work can be done in the ground or with rhizome out of the ground. Any roots or rot goes out in trash or on a burn pile.
Irises are hardy; Arlyn has cut some up into small parts and 80% have grown the following season.
The type of soil makes no difference. It is the "crawling" portion of a life cycle of a moth which lays eggs on or near the plant. Poison in or on the plant can kill the critter in the crawling stage. Nematodes can reduce the population as well. A large infestation can kill an entire bed, as noted already in the thread. Removal of dead leaves and other matter around the plants limits the places the eggs can overwinter and is probably the best thing to do.
This critter was removed, rhizome treated and is doing fine at last check several weeks from the "botanical surgery."
And a welcome to the several newcomers to the iris forums!
