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.
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 a group of insects in the suborder (Symphyta) of the Hymenoptera (bees, ants and wasps). There are about 500 species of
Adult rose slugworm 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 abundant. 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.
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. Affected areas dry up and become white or pale brown; this type of damage is known as window paining.
Rose slugworm can usually be accepted as part of the biodiversity roses support as the damage to a few leaves will not affect the vigour of plants.
Check roses frequently from June onwards so action can be taken before a damaging population has developed. When choosing management options you can minimise harm to non-target animals by starting with the methods in the non-pesticide control section and avoiding pesticides. Within pesticides the shorter persistence products (that are usually certified for organic growing) are likely to be less damaging to non-target wildlife than those with longer persistence and/or systemic action. Pesticide treatments are likely to kill natural enemies and are only likely to be successful if the entire plant can be reached.
- Where possible tolerate populations of rose slugworm, plants usually recover from defoliation with no effect on flowering
- Encourage predators and other natural enemies of sawfly in the garden, such as birds and ground beetles.
- Check plants regularly from June for the presence of larvae and remove by hand where practical
The RHS believes that avoiding pests, diseases and weeds by good practice in cultivation methods, cultivar selection, garden hygiene and encouraging or introducing natural enemies, should be the first line of control. If chemical controls are used, they should be used only in a minimal and highly targeted manner.
- If numbers of larvae are too high for hand picking, control may be achieved by spraying with pesticides. Spraying at dusk is likely to be more effective
- Organic contact insecticides containing natural pyrethrum (e.g. Bug Clear Ultra 2, Neudorff Bug Free Bug and Larvae Killer). Several applications of this short persistence products may be necessary to give good control
- More persistent contact-action insecticides include the synthetic pyrethroids lambda-cyhalothrin (e.g. Westland Resolva Bug Killer), deltamethrin (e.g. Provanto Ultimate Fruit & Vegetable Bug Killer, Provanto Sprayday Greenfly Killer) and cypermethrin (e.g. Py Bug Killer)
- A systemic containing the active ingredient Flupyradifurone (Provanto Smart Bug Killer) is available for use on ornamentals and selected edibles
- The systemic neonicotinoid insecticide acetamiprid (e.g. Bug Clear Ultra) is also available
Plants in flower should not be sprayed due to the danger to bees and other pollinating insects.
Inclusion of a pesticide product does not indicate a recommendation or endorsement by RHS Gardening Advice. It is a list of products currently available to the home gardener.
Pesticides for gardeners (pdf document outlining pesticides available to home gardeners)
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