Answer: Hi-Yield 38 Plus is a broad spectrum insecticide that will virtually eliminate all insects wherever it is applied. I just read the label and borers are listed, as are herbaceous ornamentals (which would include your iris). You need only 1/4 tsp. per gallon of water. It's pretty powerful stuff and if you only intend to use it in your iris bed, it might take a lifetime to use it up! Perhaps you can return it to the store?
Iris borers are a royal pain, but here are a few things you can do:
Keeping a clean garden is the first step in minimizing borer problems. In the summer and fall, the borer moths lay their eggs on the iris foliage or on the foliage of nearby plants. In the fall, cut back the iris leaves and remove them from your property if possible. This will reduce the number of borers hatching next spring.
In the spring, watch for the signs of borer infestation. A sharp eye for borer entry allows some gardeners to catch the borer in the leaf before it travels to the rhizome (simply pinch them in the leaves). If the borer has chewed its way further down the leaf, it maybe easier to remove a portion of the leaf then search for and destroy the borer.
Imidacloprid is a systemic, persistent pesticide manufactured by Bayer Corp. with low toxicity to mammals. Merit is the brand marketed for home use. To control borers, Merit only has to be applied once in the spring. As with all pesticides, read the directions carefully and follow them. Do not apply near vegetables or plants that will be eaten.
If you cannot locate Merit in your area, Bayer Advanced Lawn Season Long Grub Control Ready to Spread Granuals is an alternative. This product contains Merit and might be easier to find. Make sure that you are buying Season Long Grub Control or a product with Merit because Bayer Advanced Lawn has several grub formulations that do not contain Merit and have other more toxic pesticides.
Hope this helps you control the borers!
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