University of Maryland Extension

Iris Borer - Flowers

damaged iris foliage

Back to Common Problems - Annuals, Bulbs, Groundcovers, Perennials, and Vines

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 1and 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.

Management: 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.

Photo Gallery:

damage to iris stems

Damage to stems from Iris borer                                  

damaged rhizome

Iris borer larva and feeding damage

damage to stem and rhizome

Iris borer damage to stem and rhizome

Maintained by the IET Department of the College of Agriculture and Natural Resources. © 2017. Web Accessibility