Flea beetles with suspected resistance to pyrethroids needed

Oilseed rape growers and agronomists are being asked to submit live samples of cabbage stem flea beetle (CSFB) to be tested for resistance to insecticides.

Over the past few years, work funded by the Agriculture and Horticulture Development Board (AHDB) has tracked the rise of flea beetle with resistance to pyrethroid insecticides.

The AHDB is asking growers to send flea beetle samples from across the winter oilseed rape production area to Rothamsted Research, to provide an accurate picture of resistance in the UK.

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Steve Foster, who co-ordinates the screening work at Rothamsted Research, said: “We’ve already received many samples from the South East this season, but we need more samples from other parts of the UK too, including Scotland.

“So far, 25 samples have been screened at the equivalent of a full field rate pyrethroid application. Of these samples, many were relatively resistant.”

A recent spike in reports of flea beetle damage to emerging oilseed rape highlighted the problem of resistance to pyrethroid insecticides.

Growing resistance

Data from 2016 shows about 60% of the CSFB population in the UK is pyrethroid resistant and this resistance applies across all pyrethroids.

Continued monitoring of resistance levels will allow the industry to better understand the scale of the problem and find the most appropriate solution.

A 2013 ban on the use of neonicotinoid seed treatments means flea beetle control is reliant on the use of foliar pyrethroid sprays, which are far less effective, to tackle these damaging crop pests.

The unseasonably warm weather has increased flea beetle infestations and left many struggling to establish oilseed rape crops.

Risk-based approach

The AHDB says any decision to apply pyrethroid insecticides must be based on risk. 

Failure to do this will place additional selection pressure on resistance mechanisms and could result in further control issues in years to come. 

If a pyrethroid application is deemed necessary, it should be applied at full recommended field rate. 

For details on how to submit samples and guidelines, see the AHDB website.