Irish borer

Damage caused by iris borer

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.

Facts (show all)

+Common names

• Iris borer

+Scientific name

• Macronoctua onusta

+Identification

Adults: Adult moths of iris borer are with dark brown forewings and yellowish brown hindwings.

Eggs: Eggs of iris borer are creamy in color and oval in shape.

Larvae/Caterpillars: Mature larvae of iris borer are creamy pink in color and about 2 inches long.

Pupae: Pupae of iris borer are dark brown in color.

+Biology

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.

+ Organic Control of irish borer

• Following beneficial bugs and plant products are used for organic control of irish borers

+Beneficial entomopathogenic nematodes

• Steinernema carpocapsae
• Steinernema feltiae
• Heterorhabditis bacteriophora

Click each of the following beneficial bugs or plant product for more information on their rates and methods of applications for the effective control of the iris borers