Rose leaf-rolling sawfly

What is rose leaf rolling sawfly?

Rose leaf-rolling sawfly is an insect pest of roses. Female sawflies insert eggs into rose leaflets, and while doing so, secrete chemicals that induces the leaf rolling. Caterpillar-like larvae emerge from the eggs and feed within the rolled leaflets.

Attacks are particularly severe if there is warm weather during the egg-laying period in late spring-early summer, as this increases the sawfly’s activity.

Symptoms

You may see the following symptoms:

• Leaf margins curl downwards and inwards along their length until affected leaflets are rolled into tubes. This occurs during late April to early June, and takes place within 24 hours of an egg being inserted into the leaf
• Pale green larvae feed inside the rolled leaves. The remains of rolled leaves stay on the plant throughout summer

Control

Light infestations can usually be tolerated, but where a large proportion of foliage has been affected, the plant may suffer a loss of vigour.

Non chemical control

Pick off affected leaves and dispose of them before the larvae complete their feeding; this is only feasible when comparatively few leaves are affected. The removal of large numbers of leaves would be more harmful to the rose than the pest damage. Cultivation of the soil around roses during the winter may expose overwintering larvae, but may also damage the roots and encourage suckering.

Chemical control

It can be difficult to prevent the females laying eggs and initiating the damage. Pesticides often do not reach the larvae in the rolled leaves.

Deltamethrin (Bayer Sprayday Greenfly Killer) or lambda cyhalothrin (Westland Plant Rescue Fruit & Vegetable Bug Killer) will control the adult sawflies but as these are active over a six to eight week period in late spring-early summer, several applications would be necessary to prevent egg-laying.

The systemic insecticide thiacloprid (Provado Ultimate Bug Killer Ready To Use or Provado Ultimate Bug Killer Concentrate 2) may control the larvae feeding inside the rolled leaves.

Download

Pesticides for gardeners (Adobe Acrobat pdf document outlining pesticides available to gardeners)

Biology

The adult sawfly is 3-4mm (about 1/8in) long, black in colour with two pairs of transparent wings. The females insert eggs into the leaflets during late April to early June and while doing so secrete chemicals that induce the leaf rolling.

The eggs hatch into pale green caterpillars, which grow up to 10mm (about 3/8in) long as they feed inside the rolled leaflets. During late June and July the larvae go down into the soil where they overwinter as non-feeding larvae before pupating in the spring. There is one generation per year.