Iris borer larvae initially feed at the tops of plants, chewing holes in leaves and giving leaves a ragged appearance.
They eventually create dark-streaked areas that appear watery. Larvae migrate down the plant, and then mature larvae bore into leaves a few inches above the growing medium surface. Mature larvae then feed within the rhizome, creating large tunnels. The tunneling causes plants to wilt severely and eventually rot.
The adult iris borer is a nocturnal moth with dark purple front wings and yellow-brown hind wings. Females lay eggs in plant debris. Iris borer overwinters in the egg stage.
Remove debris from adjacent areas. Clip and remove dead iris leaves and stems to eliminate any overwintering eggs. Contact insecticides need to be applied before the larvae enter leaves. Frequent applications may be necessary in the spring.
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The MSU IPM Program maintains this site as an access point to pest management information at MSU. The IPM Program is administered within the Department of Entomology, fueled by research from the AgBioResearch, delivered to citizens through MSU Extension, and proud to be a part of Project GREEEN.