Rose slug sawfly or slugworm

The grazing activities of the slug-like larvae of the rose slugworm sawfly can cause leaves on roses to turn brown and dry up.

Rose slug sawfly ( Endelomyia aethiops ) on rose

Rose slug sawfly (Endelomyia aethiops) on rose

Quick facts

Common name Rose slug sawfly or slugworm
Scientific name Endelomyia aethiops
Plants affected Roses
Main symptoms The surface of leaves is grazed away and the grazed areas dry up and turn brown.
Most active June to October

What is rose slugworm?

Rose slugworms are the larvae of a sawfly. Sawflies are in the same group of insects as bees, ants and wasps (the Hymenoptera). They have caterpillar like larvae that feed on plants the adults are winged insects that can appear fly-like. The adult sawflies have black bodies about 4-5mm long and two pairs of dusky transparent wings, they emerge during mid May to mid June.

Eggs are laid on the foliage and they hatch into larvae that are black with a slug-like appearance. They are pale yellowish-green with light brown heads. Their bodies are translucent and the gut contents can often be seen as a dark green line inside the body. The larvae grow to a length of about 10mm and are somewhat club-shaped with the head end being swollen. When fully fed the larvae go into the soil to pupate.

There are two or sometimes three generations a year between June and October. The second generation in July and August can be the most damaging. Larvae that complete their feeding late in the year overwinter in cocoons in the soil before pupating in April to May of the following year.

Symptoms

This sawfly does not cause any distortion of the foliage and the caterpillars feed exposed on the leaf surface. They are normally found on the underside of leaves but will feed on the upper surface if the plant is shaded.

The larvae do not make holes in the leaves but graze away the leaf surface until only the epidermis remains. Damaged areas dry up and become white or pale brown; this type of damage is known as window paining.

Other species of slugworm cause similar damage on pear, cherry, lime, oak and willows, but these insects are not found on roses.

Control

Light infestations can be tolerated as the damage to a few leaves will not affect the vigour of plants.

Non-pesticide control

Regularly check the plant from late May onwards for slugworm larvae and if feasible pick them off by hand.

Pesticide control

  • If infestations are too heavy for hand picking, control may be achieved by spraying with pesticides. Spaying at dusk is likely to give the best results
  • Organic contact insecticides containing natural pyrethrins (e.g. Bug Clear Gun for Fruit & Veg, Ecofective Bug Killer). Several applications of these short persistence products may be necessary to give good control
  • More persistent contact insecticides include the synthetic pyrethroids lambda-cyhalothrin (e.g. Westland Resolva Pest Killer), deltamethrin (e.g. Provanto Ultimate Fruit & Vegetable Bug Killer) and cypermethrin (e.g. Py Bug Killer)
  • The systemic neonicotinoid insecticide acetamiprid (e.g. Bug Clear Ultra) is also available
  • Follow label instructions when using pesticides
  • Plants in flower should not be sprayed due to the danger to pollinating insects
  • Inclusion of a pesticide product does not indicate a recommendation or endorsement by the RHS. It is a list of products currently available to the home gardener

Downloads

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


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