Pear and cherry slugworm

The grazing activities slug-like larvae of the pear and cherry slugworm sawfly can cause some leaves on pears, cherries, hawthorn, plum, Cotoneaster, Chaenomeles and Sorbus to dry up and turn brown.

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Pear and cherry slugworm (Caliroa cerasi) on pear

Quick facts

Common name: Pear and cherry slugworm
Scientific name: Caliroa cerasi
Plants affected: Pears, cherries, hawthorn, plum, cotoneaster, chaenomeles and sorbus
Main symptoms: The upper surface of leaves is grazed away and the grazed areas dry up and turn brown
Most active: June to October

What is pear and cherry slugworm?

Pear and cherry slugworms are the larvae of a sawfly. Sawflies are a group of insects suborder (Symphyta) of the Hymenoptera (bees, ants and wasps). There are about 500 species of sawfly in Britain. They have caterpillar like larvae that feed on plant material and are named after the saw like egg laying organ used by females to lay eggs in plant material. Adults can come in a range of colours many are black, green orange or striped yellow and black. Most are small (< 1cm) but some species such as the Birch sawfly (Cimbex femoratus) can be over 2 cm long. Several species can be found in gardens and are part of the biodiversity a healthy garden will support. More information can be found at The Sawflies of Britain and Ireland webpages

Adult pear and cherry slugworm have black bodies about 4-6mm long and two pairs of transparent wings. Eggs are laid on the foliage and they hatch into larvae that are black with a slimy slug-like appearance. The larvae grow to a length of about 10mm and are somewhat club-shaped with the head end being wider than the rear. When fully fed the larvae enter 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 obvious. 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

The larvae feed by grazing away the upper surfaces of the leaves and the remaining portions of the grazed areas  dry up and turn brown.

Control

This insect can usually be tolerated. Occasionally large numbers can affect the appearance of the trees but the long term heath and on fruit trees the crop, is usually unaffected. 

Check susceptible plants frequently from spring onwards so action can be taken before a damaging infestation has developed. When choosing control options you can minimise harm to non-target animals by starting with the methods in the non-pesticide control section. If this is not sufficient to reduce the damage to acceptable levels then you may choose to use pesticides. Within this group the shorter persistence pesticides (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.

Non-pesticide control

  • Where possible tolerate populations of slugworm sawfly, sawflies can be part of the biodiversity a healthy garden supports. This species rarely affects cropping 
  • Encourage predators and other natural enemies of sawfly in the garden, such as birds and ground beetles.
  • Check plants regularly from April for the presence of larvae and remove by hand where practical
Pesticide control

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.
  • Pear and cherry slugworm does not usually require control.  numbers of larvae are too high for hand picking, control may be achieved by spraying with pesticides. Spraying at dusk is likely to give the best results
  • Organic contact insecticides containing natural pyrethrinrum (e.g. Bug Clear Gun for Fruit & Veg, 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
Follow label instructions when using pesticides. On edible plants make sure the food plant is listed on the label and follow instructions on maximum number applications, spray interval and harvest interval. 

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.

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Pesticides for gardeners (pdf document outlining pesticides available to home gardeners)

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