Why Are My Rose Leaves Being Skeletonised?

Rose leaves reduced to a pale, translucent skeleton of veins — with all the green leaf tissue between them eaten away — are the work of rose slugworm, the larva of a sawfly called Endelomyia aethiops. Despite the name, this pest is not a slug at all. It is a wasp-like fly whose pale, yellowish-green larvae feed on the surface of the leaf, grazing away the upper tissue without penetrating right through. The result is a characteristic windowed or skeletonised pattern that turns brown and papery as the damaged area dies.

Identifying the larvae

The larvae are small — about 10–12 mm when fully grown — pale greenish-yellow and slightly shiny, resembling a tiny slug in texture. They feed on the upper surface of the leaf, working in a characteristic pattern that leaves the veins intact. You will find them on the upper side of the leaf in the early stages, moving to the undersides as they mature. The adult sawfly is small and inconspicuous, resembling a wasp without the narrow waist, and lays eggs into the leaf tissue in late spring.

Impact on plant health

A single generation of rose slugworm on an otherwise healthy plant rarely causes lasting harm. The skeletonised leaves are unsightly and reduce the plant's photosynthetic capacity temporarily, but new leaves replace them. However, when two or three generations occur in sequence — or when the infestation is heavy — significant defoliation can follow, weakening the plant heading into autumn and reducing flower production. Young roses and plants already stressed by drought or disease are more vulnerable than established, well-fed specimens.

Hand-picking

As with most small caterpillar-like pests, hand-picking is the most targeted and environmentally friendly approach. Inspect the plants every few days from late May onward, checking both leaf surfaces and picking off larvae into soapy water. Squashing groups of young larvae on the leaf is also effective. The larvae do not move quickly and are easy to find once you know what you are looking for. Daily checks for a week at peak time will dramatically reduce the population without affecting beneficial insects.

Water jets and soap sprays

A firm jet of water washes larvae off the leaves and disrupts feeding. Larvae knocked to the ground do not usually climb back up. Insecticidal soap sprayed directly onto the larvae kills them on contact by interfering with their cell membranes. Coverage of the upper leaf surface, where the larvae feed, is important. Apply soap spray in the morning when larvae are active. Repeat after rain or every 5–7 days while larvae are present.

Pesticide options

For severe infestations, pyrethrin-based sprays provide effective knockdown of larvae. These degrade quickly and have lower persistence in the environment compared to synthetic pyrethroids. Apply in the evening to reduce risk to foraging insects. Contact insecticides work well against rose slugworm larvae because they feed on the open leaf surface where the spray lands. Systemic products are unnecessary for this pest and should be avoided to protect pollinators and natural enemies.