Thrips treatment trials make progress

Biological and conventional controls are being explored to counter growing infestation problems.

Measures to counter the growing problem of infestation of soft fruit by western flower thrips (WFT) was the subject of two presentations at the recent Soft Fruit Day.

Originally from North America, WFT (Frankliniella occidentalis) has been detected on many food and ornamental crops and has been found to overwinter in strawberry fields, the audience at the East Malling Research Association/Horticultural Development Company (HDC) sessions heard.

"It causes bronzing on strawberries that makes the fruit unmarketable," said ADAS senior entomologist Jude Bennison. She is leading a five-year HDC and HortLINK-supported project to assess a range of biological and conventional controls with the aim of prescribing a full integrated pest management programme.

The mite Amblyseius cucumeris "can be unreliable" as a predator, while WFT is also showing signs of resistance to conventional pesticides, she added.

The flower bug Orius laevigatus also predates on WFT, Bennison explained. "But they are expensive and slow to establish, particularly when there are few flowers because they feed on pollen too. They are also sensitive to chemicals."

For this reason, the trial looked at incubating Orius in Alyssum plants, alongside Amblyseius, in tests that took place at Sunclose Farm in Cambridgeshire.

The combination of the two predators gave good control of thrips, she said. However, the effect of providing Alyssum banker plants had no effect on numbers of either WFT or Orius on strawberry plants.

Another approach to WFT control put forward by Keele University senior lecturer Dr William Kirk was to mimic signal chemicals (semiochemicals) emitted by the males.

His own work had revealed the chemical structure of WFT's aggregation pheromone, a precursor to mating, and this has since been commercialised by Syngenta Bioline.

Meanwhile, Koppert has developed Lurem-TR, which replicates a kairomone or attract chemical from the plant itself.

A HortLINK-supported project is now seeking to develop a pest-specific "sticky" monitoring trap using either or both of these, and to establish damage thresholds, he said. The colour of sticky trap has a bearing on their attractiveness to WFT, he added.

"If you get the right shade of blue, you will trap a lot more than on yellow," he pointed out. "They need a combination of colour and pheromone."

Research direction

Horticultural Development Company communications manager Scott Raffle told soft fruit growers at the Soft Fruit Day: "There's a lot more on this to come. Western flower thrip is such a problem for the industry."

He added: "You can influence what research we do. It's the job of our technical manager Andrew Tinsley to shape the projects you want to fund."

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