University of Maryland Extension

Iris Borer - Flowers

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damaged iris foliage

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. The damaged leaves appear water-soaked and ragged. The larvae reach the rhizome around early July where they feed. By the time they are mature they are flesh-pink colored, with brown heads and 1 and ½ to 2 inches long. After eating out the interior of the rhizome, the larva pupates in the soil. The adults (moths) emerge and are present from August through early October, flying only at night. The female moths lay their eggs at the base of old iris leaves and debris, especially at the base of old iris plants. There is one generation of this insect each year.

damage to iris stems
Stem damage caused by iris borer

damaged rhizome
Iris borer larva and feeding damage

damage to stem and rhizome
Iris borer damage to stem and rhizome


Remove old iris leaves and stalks in the late fall to eliminate the overwintering eggs. Monitor the iris plants in the spring for mining damage caused by the young larvae. These may be killed in the leaves by squishing between your fingers. Clean up infested iris beds after flowering, by digging up the plants. Remove any rotted or damaged portions and kill any larvae that are found.


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