Diamondback moth not going away, so understanding controls is key - AHDB

UK brassica growers should expect ongoing problems with diamondback moths, though improved understanding of their susceptibility to chemical control should help to better deal with them in future, delegates at an AHDB Horticulture workshop heard.

Image: Patrick Clement (CC BY 2.0)
Image: Patrick Clement (CC BY 2.0)

Resistance research at Rothamsted Research has established baselines for testing diamondback moth (Plutella xylostella) samples for the first time, as well as confirming the moths' resistance to pyrethroids, the gathering of some 60 growers, agronomists and agro-chemical company representatives heard.

Rothamsted research scientist Dr Steve Foster said: "We tested a range of different chemical insecticides for their effectiveness against the larvae of the moths that we saw last year. Some compounds were effective, but the commonly used pyrethroids were not, due to strong resistance."

He warned: "If large numbers of new moths arrive in the UK in future years – a scenario which is becoming more likely due to climate change – they could carry different forms of resistance, so future outbreaks may respond differently to insecticide sprays."

But this latest research will enable the industry to respond to future outbreaks more quickly, he added. "We will now hopefully be able to identify effective control measures of future outbreaks within weeks, not months."

Diamondback moth caused unprecedented damage to brassica crops last season, but collaboration between AHDB Horticulture, Warwick Crop Centre, Rothamsted Research and Brassica growers has ensured a better understanding of the pest and effective measures against it.

Andrew Rutherford, R&D Committee Chairman of the Brassica Growers Association, said: "Historically, we have considered diamondback moth to be a sporadic pest but we now think it is a problem that is here to stay."

AHDB Horticulture knowledge exchange manager Dr Dawn Teverson added that while growers mainly responded to last year's outbreak with pyrethroid sprays, "we now know that this may, unfortunately, have exacerbated the problem, as not only were the moths resistant but it may have led to a loss of beneficial biological control insects, such as parasitoid wasps, which could have helped manage pest numbers".

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