Iris sawfly

The greyish-brown caterpillar like larval stage of iris sawfly can completely defoliate flag iris and other waterside iris in summer.

Iris sawfly ( Rhadinoceraea micans ) on yellow flag iris ( Iris pseudacorus )

Iris sawfly (Rhadinoceraea micans) on yellow flag iris (Iris pseudacorus)

Quick facts

Common name Iris sawfly
Latin name Rhadinoceraea micans
Plants affected Flag iris (Iris pseudacorus) and other waterside irises
Main symptoms The foliage is eaten by greyish brown caterpillar-like larvae
Caused by Larvae of a sawfly
Timing April-July

What is iris sawfly?

Iris sawfly has greyish-brown caterpillar-like larva that reach 25 mm in length and eat the foliage of flag iris (Iris pseudacorus) and other waterside irises, including Iris spuria, I. versicolor, I. laevigata and I. ensata. The adults are similar in appearance to some other species of sawfly and have black heads and bodies up to 8mm long with smoky grey wings.

Symptoms

Iris sawfly larvae can feed in groups so damage can occur very quickly and defoliation can be extensive. Keep vigilant for early signs;

  • Greyish-brown caterpillar-like larvae with whitish spots brown heads and up to 25 mm long
  • Initially V-shaped notches from the leaf margins but later devour the foliage from the leaf tips downwards
  • Plants can be completely defoliated, affecting their appearance and vigour

Control

Non chemical

Regularly inspect plants during the growing season and where possible remove larvae from the leaves.

Chemical

Insecticides cannot be used against this insect because of the danger to fish, frogs, toads and other aquatic life in water bodies where irises grow.

Biology

Iris sawfly adults are active in late April-May and soon lay eggs on the foliage of host plants. The greyish-brown caterpillar like larvae, speckled with small white spots and up to 25mm long, are present in June-July. The larvae initially eat V-shaped notches from the leaf margins but later devour the foliage from the leaf tips downwards.

There is one generation a year and larvae overwinter in the soil before pupating in the following spring.


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