What's eating my iris laevigata?

Iris laevigata (Japanese rabbit-ear iris) is a true aquatic marginal susceptible to iris sawfly in the UK and iris borer in North America. Slugs damage new spring growth at the water's edge. Remove sawfly larvae by hand, destroy borer-infested rhizomes, and use iron-phosphate bait for slug control.

Larvae notch leaf edges in a characteristic top-down manner, rapidly consuming large sections of foliage in late spring and summer. Hand-pick larvae; check plants daily at the peak larval period. Drop larvae in soapy water. No chemical spray usually required.

Larvae tunnel into rhizomes, causing ragged streaks on leaves and rotting, hollowed rhizomes that may cause entire fans to collapse. Remove and destroy infested rhizomes. Clear dead foliage every autumn to destroy overwintering eggs. Nematode drenches targeting borer larvae can be applied in spring.

Emerging shoots at the water margin are rasped at night, leaving irregular holes or completely severed young spikes in spring. Iron-phosphate slug pellets are safe near pond margins and wildlife. Hand-pick at dusk. Avoid metaldehyde-based baits near water (UK banned metaldehyde outdoors since 2022).