Research unveils IPM-based control methods for Thrips palmi on cucumbers

Future outbreaks of the quarantine pest Thrips palmi on cucumbers could be controlled using integrated pest management - rather than pesticides that would render the crop unsaleable - following research instigated by the Cucumber Growers' Association (CGA).

"Defra's Plant Health & Seeds Inspectorate (PHSI) is revising its contingency plans for the pest, and inspectors will be trained in using the IPM techniques in the event of an outbreak," said Keith Walters, head of Central Science Laboratory's Environmental Biology Group, at last month's CGA technical conference in Peterborough.

He added: "As far as I know, this is the first example of a grower association taking a lead in working with Defra and the PHSI to develop such a strategy. It is very welcome as it means we can ensure we undertake research that results in practical measures that can be used on crops."

As T. palmi is a quarantine pest, outbreaks need to be completely eradicated from a glasshouse, rather than simply being restricted to numbers that don't cause economic damage to the crop.

CGA secretary Rob Jacobson said that the last outbreak in a cucumber crop, in 2002, was eradicated using intensive pesticide treatments that caused more damage to the crop than the pest had. He said: "That's why we decided we needed to work with the PHSI to develop an alternative strategy based on IPM."

T. palmi is difficult to control using pesticides because of its small size, rapid life-cycle and the fact that it hides itself within buds and other plant crevices. On cucumbers it causes scarring on fruits, making them unmarketable, and can defoliate or weaken plants as well as spread diseases.

The control strategy combines existing biological control agents and short-persistence insecticides.

Should the pest arrive on imported plants, short-persistence insecticides like abamectin, spinosad or thiacloprid would be used first, two to three days after planting, followed by species of Amblyseius predatory mites two days later. The rove beetle Atheta coriaria or Hypoaspis mites, released into the rootzone two to three weeks after planting, can control larvae that fall there to pupate.

Once the pest population has been suppressed, applications of the bioinsecticide Mycotal, or possibly thiacloprid through the irrigation system, can clean up what is left. Eradication from the growing slabs can be achieved at this stage using sticky barriers, or repeated aerial insecticide treatments to reduce the numbers of new pupae.

Further releases of Hypoaspis or Atheta could also be made while the nematode Steinernema carpocapsae could be used in soil-based organic crops.

"We have not been able to test the protocol in a greenhouse because it is a quarantine pest. We will only be able to test it on a real outbreak - when it has to work," said Walters.

However, laboratory experiments have shown Amblyseius can control T. palmi numbers as effectively as a single spray of spinosad.

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