Diamondback moth resistant to pyrethroids

Further evidence of pyrethroid resistance in Diamondback moths (DBM) has been uncovered by a new study.

Three DBM samples, from Lincolnshire, Suffolk and Scotland, tested by researchers at Rothamsted Research were all found resistant to this class of insecticides.

Now AHDB Horticulture has organised a workshop in January to give the industry an opportunity to discuss the implications of the findings on future pest management.

Rothamsted’s Dr Steve Foster, who led the research, said: “Pyrethroids are normally the first choice of insecticides against moth pests but these tests indicate that resistance is present in the DBM population over a wide geographical spread”.

“If growers continued to use pyrethroids, this could be doubly damaging – not only would it not have an effect on DBM, it would be killing beneficial insects which attack DBM.”

DBM causes cosmetic and feeding damage in Brassica crops that can result in up to 100 per cent crop loss.

Pyrethroid resistance was initially confirmed in one DBM sample from Lincolnshire in August. AHDB worked together with industry to produce an emergency 120-day authorisation for Benevia 10OD for use as an insecticide on a range of Brassica crops for DBM control.

In the latest project, Dr Foster and Dr Martin Williamson tested three additional DBM caterpillar samples for resistance to a range of insecticides. January’s workshop will see Dr Foster present his findings and give Brassica growers, agrochemical companies and researchers the opportunity to discuss the situation in 2016 and develop strategies to manage similar outbreaks in the future.

Dr Foster said: “I will be presenting data on which insecticides worked for DBM control and which didn’t, so growers and agronomists know what to use and importantly, what not to use against this pest in the UK”.

“For instance, the Benevia approval meant growers had a product available that would work well alongside products containing spinosad as an active ingredient. Spinosad has a different mode of action to pyrethroids, so is good for resistance management,” said Steve.

“It is important to remember Benevia does not currently have full label recommendation from the Chemical Regulation Directorate, this is an area I will be working on with AHDB,” he added.

The Diamondback moth workshop will be held at PGRO, Peterborough, on 24 January 2017. Event and booking information is available on the AHDB Horticulture website, horticulture.ahdb.org.uk/events