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I have an iris garden that I inherited when we bought our house, and have been reading up on caring for them. Can anyone tell me what borers look like and how I will know if I have them? Should I treat for them regardless of whether or not I can see any?
I inherited a vast iris garden when I bought my house, too, and there were no iris borers in sight -- but the plants were terribly overgrown, crammed together and growing on top of each other, and they were all white, which meant that against the white siding they disappeared the moment they bloomed. So last fall I dug most of them out and replaced them with multi-colored irises, which are growing like gangbusters.
So I'd recommend you just wait a month or so, see how your inherited irises look when they grow and bloom. Iris borers will produce stunted, distorted plants, but do differentiate between those and babies from very young small rhisomes. My understanding is that irises afflicted with iris borers are goners, so you may as well wait, see, and then remove any irises that don't please you for whatever reason.
Around here, the borers can come and go. I don't take precautions, and have plenty of iris survive and bloom. I'd go with carrie- just watch how they bloom, then as the foliage dies down in summer, dig up, save the best looking parts, (fan of leaves with a piece of horizontal rhizome and some vertical roots going down) discard yucky parts, replant Toss the littlest parts, the long old rhizome that has no roots going down from it, and any rhizomes that have tunnels eaten into the bottoms. Those are the borer tunnels, you won't see them from the top. Fertilize, 6-10-10 if you can find it, but anyway not too high on the first number.
In case those borers are wire worm, a solution would be to cut some potatoes in half, put a stick large enough to show when the potatoe is buried in the uncut end, and place them a few inches down in various places around the iris beds. Leave them in a few days, then remove them. Wire worm love potatoes, and will bore into them. destroy the potatoes, don't put them in your compost.