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Extension > Garden > Diagnose a problem > What insect is this? > Garden Pests > Caterpillars, maggots, grubs, and similar immature insects - Larger than 3/4 inch long > Iris borer

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Iris borer

Macronoctua onusta

Iris borer

Jeff Hahn, University of Minnesota

Iris borer

Mary Lou Marchand

Size: Up to 2 inches long

Where/When: Tunnels inside iris leaves, eventually moving down into the rhizome. Active from April through early August.

Significance: Damage to the rhizome is often considerable, although the iris is not immediately killed. Feeding damage can allow the entry of a bacterial soft rot. Rhizomes infected by soft rot are slimy, soft and foul-smelling and can kill iris.

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