What's eating my iris pseudacorus?

Iris pseudacorus (yellow flag iris) is a robust native pond marginal attacked mainly by iris sawfly larvae in the UK and iris borer in North America. Deer and rabbits browse foliage where plants grow at accessible pond margins. Slugs attack emerging shoots. Hand-removal of sawfly larvae is usually sufficient control.

Grey-blue larvae work down the leaf, notching edges in a distinctive staircase pattern; heavy infestations leave little more than leaf midribs. Hand-pick larvae and destroy. Daily inspection in May–June is usually sufficient. No pesticide spray is needed for typical garden infestations.

Borer caterpillars tunnel leaves and rhizomes, causing wet rotting streaks on foliage and hollowed, foul-smelling rhizomes. Remove and destroy borer-infested rhizomes. Clear all dead foliage in autumn. Apply predatory nematodes (Steinernema carpocapsae) as a spring soil drench near rhizomes.

Deer browse emergent leaves and flower stems at accessible pond margins, especially in spring when new growth is tender. Fence the pond margin or apply deer repellent to foliage. I. pseudacorus spreads vigorously, so severe browsing rarely kills established clumps.

Rasped holes in emerging spring shoots at the water margin; worse in wet years when slug populations peak. Iron-phosphate pellets at the pond margin. Hand-pick at night. Ducks in the pond will naturally reduce slug pressure.