Dates: April 2008 - March 2012

Funding: DEFRA Horticulture

Countries: UK

Collaborators: East Malling Research

NRI Project Leader: David Hall

Background

Cacopsylla pyricola summer form © University of Greenwich

Over 173,000 t of pears worth £225 m are currently consumed in the UK. However, domestic production is only 23,000 t worth £30 m and produced from 1540 ha. Over 87% is imported from such countries as Belgium and The Netherlands. The low level of production in the UK is due to low yields from old rootstock and damage caused by pear sucker. This has resulted in a lack of confidence to invest in new, intensive and high-yielding pear orchards. The main species of pear sucker in the UK is Cacopsylla pyricola. The nymphs suck sap from the leaves and fruits, excreting honeydew which turns black with sooty mould and ruins the crop. Attacks weaken the trees with severe reduction in fruit buds the year following attack. Pear sucker nymphs are also vectors of the pear decline phytoplasma. The pest is favoured by warm dry conditions, but not drought stress. Rainfall, especially heavy, causes high mortality with young nymphs being particularly vulnerable. If the UK becomes warmer due to climate change this will favour pear growing but will also exacerbate the problem of pear sucker. Control of pear sucker is currently very difficult. The pest is resistant to a range of insecticides. The most effective, Amitraz, is now not available, and other insecticides are of limited efficacy. Alternative control measures such as sprays of sulphur and wetting agents are used but it is uncertain how effective they are. Anthocorid bugs are voracious predators of all life stages of pear sucker, but they generally do not overwinter in pear orchards and only migrate into orchards 3-4 weeks after blossom by which time the pear sucker is well-established.

Objectives

Cacopsylla pyricola five nymphal stages © University of Greenwich

The overall aim of the project is to develop improved Integrated Pest Management methods for pear sucker. The following approaches will be investigated.
1. Sex pheromone monitoring. Females of C. pyricola and other species of psyllid have been shown to produce a sex pheromone that attracts males. American and Israeli researchers are working on identification of this, and if a synthetic pheromone becomes available it will be evaluated for monitoring pear sucker in the UK.
2. Conservation biocontrol. The effects of various types of hedgerow, border vegetation and ground herbage in the orchard alleys on encouraging early and extensive immigration of anthocorid predators will be studied.
3. Synthetic synomones to attract anthocorids. The is evidence that the anthocorid predators are attracted by compounds produced by pear trees when attacked by pear sucker. These will be identified and the synthetic compounds evaluated for their ability to encourage early and extensive immigration of the predators.
4. Selective physical controls. The effectiveness of various treatments such as sulphur, wetting agents and kaolin will be studied for their effectiveness against pear sucker and any effects on natural enemies.

If successful, the project will result in an integrated programme giving improved control of pear sucker with reduction in the use of insecticides. This should lead to increase in confidence in pear growing in the UK with greater domestic production and reduction in imports.

Industry partners are H Chapman Ltd, D G Long, J L Baxter & Son, Robert Mitchell Partnership, H Rudge, G H Dean Ltd, WorldWideFruit, English Apples & Pears Ltd, Agrisense BCS Ltd, FAST Ltd, UAP Ltd, H L Hutchinson and J Sainsbury plc. Joint funders include the Horticultural Development Council, The East Malling Trust for Horticultural Research and East Malling Ltd.