An increasingly common pest of waterside irises, causing damage through defoliation.
Hosts
Iris pseudacorus, I. spuria, I. versicolor, I. laevigata and I. ensata.
Other irises growing away from water are not attacked.
Symptoms
Greyish brown caterpillar-like larvae, up to 25mm long, defoliate irises growing near ponds, lakes and canals. Initially the larvae eat V-shaped notches in the leaf margins but later most of the upper leaf blade is eaten down to the central portion.
Biology
The adult sawfly has a black body with two pairs of dark grey wings. The females lay eggs on iris leaves in late April-May. The larvae are present in June-July and go into the soil when fully fed. Iris sawfly is widely distributed in England and Wales, but it does not attack irises that grow in dry soils.
Control
Although young sawfly larvae are susceptible to insecticides it is not possible to use them because of the danger to fish, frogs, toads and other pond wildlife. Sawfly larvae can be removed by hand, but if this is not feasible, the damage has to be tolerated. The irises will survive, although the foliage will have a ragged appearance from midsummer onwards.