Leaves ragged with dark spots? Pink caterpillars munching your iris? Find out how to control borer damage and rid yourself of moths.
What is it?
Damage to the leaves and eventually the rhizome caused by the larva of the iris borer, a night-flying moth which is one of the most destructive insect pests to this plant.
What does it look like?
Slits, water-soaked spots and dark streaks in new leaves, or leaves which look ragged and chewed. The foliage becomes wilted and discolored, and the leaf bases become loose and rotted. Eventually the rhizomes become filled with holes and may be soft and rotted. Pink caterpillars from 1 to 2 inches long may be visible feeding inside the rhizome.
How does it manifest?
The adult female moth lays eggs in old stalks and leaves in autumn. Eggs hatch in late April or early May with emerging larva feeding on leaf surfaces initially. Then they bore into the inner tissue of the leaves and eventually mine down into the rhizome. The damaged rhizome becomes susceptible to bacterial soft rot. The larvae exit the rhizome and pupate in the soil, emerging as adult moths in the fall.
What can you do about it?
To eliminate borer eggs, clean up and destroy plant debris in the fall or by early April. From the time iris growth begins until mid-June, spray infested plants weekly with an insecticide containing lindane. In May and June leaves can be squeezed in the area of the feeding damage to kill the borers inside. Heavily infested plants must be destroyed. However, borers can be killed in lightly infested plants by poking a wire into the holes.