Fly pest threatens 'catastrophic losses'

Soft Fruit Day hears entomologist call for action to tackle potential crop losses threatened by spotted-wing Drosophila.

The recently arrived soft and stone fruit pest the spotted-wing Drosophila (SWD) "will cause serious, perhaps catastrophic losses if measures are not put in place", East Malling Research (EMR) entomologist Professor Jerry Cross warned at last week's Soft Fruit Day at the Kent research station.

Having researched the industry response to the pest in continental Europe and North America, where SWD is already established, Cross said: "Monitoring is very important because infested fruit mustn't be sent to market - it will affect your neighbours and your industry."

The fly was first recorded in the UK at EMR in August this year. "It's not easy to identify, especially the females, and you can't identify the larvae until they mature," said Cross. "The life cycle takes just 20-30 days so you get multiple generations each season. And the temperature and humidity in our polytunnels are ideal for them, perhaps more so than in southern Europe."

He admitted that putting out traps "is very labour-intensive, but European growers think it's worth it", and explained: "We have devised a simple monitoring trap that keeps the flies away from the bait of fermenting yeast and sugar solution."

When the pest is discovered, he said: "You need to prevent them laying - they will have to be sprayed every five-to-seven days. However, we only have chlorpyrifos, pyrethroids, Spinosad and neonicotinoids, which are harmful to predators so will disrupt integrated pest management programmes.

"Also, there are no approved pesticides for blueberry and cherry in the UK, though the Horticultural Development Company is trying to address that with the Chemicals Regulation Directorate."

But he warned of a high risk of resistance. "We need to maximise use of non-pesticide methods." Dealing with infested and vulnerable plant material is essential but "difficult and costly". He suggested: "Closed composting is probably best."

Cultural control can keep pest populations to a minimum

"As the Horticultural Development Company recommends, a good degree of cultural control, in particular removing leftover fruit, is essential to keep spotted-wing drosophila populations low, but in severe cases Spinosad and natural pyrethrums are available to organic growers. We will be making sure that our growers know about the risk and will be monitoring the situation over the coming year."

Ben Raskin, Head of Horticulture, Soil Association.


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