2023年3月10日 · Iris borer is the most damaging pest of iris (bearded, Japanese, blue flag, and Belamcanda). Eggs hatch in April or early May. The tiny, white larvae (caterpillars) crawl up the leaves, bore into the leaf tissue where they mine the foliage. Eventually, they work their way down to the plant by boring down the stem until they reach the rhizomes.