Symptoms

The common sign is leaf margins curling downwards and inwards until affected leaflets are rolled into tubes. The rolled leaves contain an egg or a caterpillar-like sawfly larva that feeds within the rolled leaflets.

Spot them

The adult sawfly, 3-4mm long, is black in colour with two pairs of transparent wings. The eggs hatch into pale green caterpillars, 10mm or so long, which feed inside the rolled leaflets. In late summer June and July the larvae go down into the soil where they overwinter as non-feeding larvae before pupating in the spring.