Iris borers are considered as one of the most damaging pests of irises. Only larval stages of iris borer cause damage to iris plants. Generally, newly hatched larvae find and bore into the newly sprouted iris foliage. While feeding inside the leaves, larvae tunnel through leaf tissue and move downwards to the rhizome. Once inside the rhizome, larvae feed internally on rhizome tissues. These injured rhizomes are generally infected by pathogenic bacteria, Erwinia carotovora that causes a disease called bacterial soft rot. These infected rhizomes become soft, slimy, smelly and eventually iris plants die.
Iris borers develop through four life stages including eggs, larvae, pupae and adults (moths). Female moths lay over 100 eggs in a cluster on the old iris leaves/ plant debris in late August through early September. Eggs survive severe winters in the plant debris and hatch into small larvae early in the spring. These larvae then move into newly sprouted iris foliage and bore into the young iris leaves. While feeding inside the leaves, larvae tunnel through leaf tissue and move downwards to the rhizome. Once inside the rhizome, larvae feed internally on rhizome tissue and become mature. Matured larvae then exit damaged rhizomes and move into the soil for pupation. Adult moths emerge from pupae in the fall. After mating, females lay eggs as overwintering stage and life cycle continues.