The Diamondback moth (DBM) that has been wreaking havoc across UK brassica crops has been confirmed as resistant to pyrethroid pesticides.
Growers who continue to use pyrethroids are risking harm to beneficial insects that attack DBM, as well as failing to tackle the pest itself, researchers warned.
The new study by Rothamsted Research found three DBM samples, from Lincolnshire, Suffolk and Scotland, were resistant to this group of chemicals, which are commonly used to control moths.
In response, AHDB Horticulture has organised a workshop in January to help growers discuss the findings and future pest management.
Rothamsted’s Dr Steve Foster 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 then helped to secure an emergency 120-day authorisation for Benevia 10OD for use on a range of brassica crops for DBM control.
Speaking about the content for the workshop, 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.”
Foster said growers should remember that Benevia does not have full label recommendation from the Chemical Regulation Directorate, and said he is working on securing this alongside AHDB.
The DBM workshop will be held at PGRO, Peterborough, on 24 January 2017.