Once they are in the rhizomes, about all you can do is dig every one, inspect, treat, and re-plant. I use" Bayer Long Season Grub Control", it contains" Merit", a systemic insecticide. With systemic type insecticides, you have to be pro-active, and apply them in early spring when growth starts, so they can be "taken-up" by the plant. I THINK the Grub Control is supposed to be good for 3 months( bottles are at the garage, I'll check later), but I re-apply after the last bloom is gone. Nemotodes will work, if you can catch the borers before they get into the plant. Lucy is right about the soft-rot being the big problem. A careful inspection of the leaves, starting in the early spring, and continuing till Aug., will tell you if you have them, and ,if you get them while they are still small, and in the leaves, you can squish them. I've been using the Merit for 5-6 years now, and only occasionally see where a borer has started to work, but they never get very far, before the insecticide gets them. If you grow iris east of the Rocky Mountains, there's gonna' be borers around, so you have to watch those leaves ,close, for signs.....Arlyn
