Pear and cherry slugworm

Pear and cherry slugworms are the larvae of a sawfly. Sawflies are in the same group of insects as bees, ants and wasps (the Hymenoptera). The 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 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 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.

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.

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

Non-pesticide control

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

Pesticide control

• Do not treat large trees where it is impractical to achieve good spray coverage. On large trees tolerate the presence of this insect, it will cause no long term damage
• Slugworms feed exposed on the leaf surface and so are readily controlled by most insecticides. If required a single application when larvae are seen should be sufficient
• Monitor plants for early signs of damage because larvae are more susceptible to insecticides
• 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. These products can be used on fruiting trees provided label instructions are followed
• Contact action insecticides that can be used on fruiting cherries and pears in addition to ornamental plants, include the more persistent contact insecticides include the synthetic pyrethroids lambda-cyhalothrin (e.g. Westland Resolva Pest Killer) and deltamethrin (e.g. Provanto Ultimate Fruit & Vegetable Bug Killer)
• The systemic neonicotinoid insecticide acetamiprid (e.g. Bug Clear Ultra) is also available, for use on ornamental plants only
• 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
• The label must be checked before use and manufacturer’s instructions followed especially regarding maximum number of applications and harvest interval
• 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

Download

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

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