Trials aim to control major pests on cherry

Four ambitious trials are underway at East Malling Research (EMR), aimed at finding ways of controlling cherry's major pests and diseases by non-chemical means.

The importance of this HortLINK project is indicated by the financial support of a consortium of 20 science and industry partners.

The potential value of the project was stressed by one of its industry partners, John Leigh-Pemberton of Torry Hill Farms, at EMR on 24 November. He told EMR Association members at a tree fruit day that cherry production is probably unique in the UK in failing to meet its buoyant demand.

Leigh-Pemberton said UK consumers spend around £105m annually on cherries but only about five per cent are home-grown (the figure for plums is 17 per cent).That percentage equates with some 900 tonnes, but the good news is that it will expand rapidly over the next five years or so.

"I know of several growers who are planning to double their area of cherries over the next five years," he said. "We have some excellent new varieties such as Penny and to a great extent we have solved our weather problems with rain covers and skin elasticisers."

However, the crop is prone to potentially devastating attack by pests and diseases. This problem is not being helped by the erosion of growers' pesticide armoury by EU legislation and the fact that supermarkets and consumers want residue-free produce.

One HortLINK project will therefore be developing alternative sustainable bio-control methods of combating brown rot, aphids, plum fruit moth and light brown apple moth, which has become a significant pest in recent years.

Dr Jerry Cross, who is leading the team working on the project, said brown rot frequently results in total crop loss. The disease is controlled by blossom and pre-harvest fungicide sprays but they are not very satisfactory and the pre-harvest treatment can leave residues.

"The keys to brown rot control are the elimination of overwintering inoculum (mummified fruit) and blossom infection," he said. "We're also looking at the potential of bio-control agents."

Two approaches to aphid control are being investigated. One is to kill females in the autumn before they start laying eggs. At that time they are easier to target with aphicides that pose no residue problem. The other technique is novel in that it will exploit ants' habit of consuming the honeydew produced by aphid colonies.

Cross explained that ants are abundant in undisturbed orchard soils. In return for the honeydew, ants protect the pest against predators and diseases. However, the close contact of the two can be exploited by using ants as vectors of pathogenic fungi that kill the aphids but not the carriers.

The plum fruit moth produces two generations a year, requires multiple sprays to control and commands zero tolerance in plums. To combat it biologically, the project aims to use sex pheromone-based mating disruption using a volatile chemical produced by ripening fruit to attract female moths and autumn control of the pest with sprays of pathogenic nematodes.

There is also zero tolerance to the potentially devastating light brown apple moth. The biological control methods being developed include pheromone-based attract-and-kill techniques and mating disruption, Cross explained.

The science partners making up the project's consortium are EMR, Warwick HRI, the Natural Resources Institute and the University of Kent - along with Sainsbury's, KG Growers, BerryWorld, Summer Fruit Company, Mack Multiples, Torry Hill Farms, GH Dean, FW Mansfield & Son, H Bryant, Agrisense, UAP, Hutchinsons, FAST, Stone Fruit Club, the Horticultural Development Company and East Malling Trust.

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