What's eating my iris ensata?

Iris ensata (Japanese water iris) is most commonly attacked by iris borer caterpillars in North America and iris sawfly larvae in the UK. Slugs and snails rasp emerging shoots. Aphids colonize new growth in spring. Remove and destroy borer-infested rhizomes and larvae promptly; slugs are controlled with iron-phosphate bait.

Caterpillars tunnel down from leaf tips into rhizomes, leaving ragged, water-soaked streaks on leaves and rotting, foul-smelling rhizomes that may be eaten out entirely. Cut off and destroy affected leaves in early spring before larvae descend. Dig and destroy infected rhizomes. Clean up all dead foliage in autumn to eliminate overwintering eggs.

Grey-blue larvae notch leaf edges from the top down, stripping large areas of foliage rapidly in late spring and early summer. Hand-pick larvae and drop into soapy water. One or two checks per day during the larval period are usually sufficient. No chemical sprays needed for most garden infestations.

Rasp irregular holes and channels in emerging spring shoots and young leaves, worst in wet seasons in pond-margin conditions. Apply iron-phosphate slug bait around plants (safe near water and wildlife). Lay grit or gravel mulch around crowns. Hand-pick at night.

Clusters on young leaf bases and flower stems cause distorted, sticky growth and can introduce iris mosaic virus. Blast off with water. Encourage ladybirds and lacewings. Insecticidal soap spray on foliage only if pressure is severe.