HGCA report outlines extent of cabbage stem flea beetle damage to oilseed rape crops

Adult cabbage stem flea beetle. Pic by Dewar Crop Protection.

Adult cabbage stem flea beetle. Pic by Dewar Crop Protection. - Credit: Dewar Crop Protection.

Norfolk's farms are believed to have escaped the worst damage from pests which have caused estimated losses of 2.7pc of the winter oilseed rape (WOSR) area in England.

The extent of cabbage stem flea beetle (CSFB) damage across England and Scotland following the ban of neonicotinoid seed dressings has been highlighted in a 'snapshot assessment' report commissioned by the HGCA (Home Grown Cereals Authority).

Based on the period 22–29 September, the estimated 2.7pc loss is equivalent to 18,000ha across the country, but there were significant regional variations.

The worst affected areas were in Hampshire, Bedfordshire and Hertfordshire, where more than 40pc of the WOSR was reported as having damage levels at or above treatment thresholds.

But in Norfolk, the report says no OSR crops had more than 25pc leaf damage, and the survey found no crop lost or redrilled. 70pc of the county's crop was now considered 'beyond risk stage'. The picture was worse in Suffolk, where 5pc crop was estimated to be lost and 5pc needing to redrilled.

Tim Issac, east regional manager for the HGCA, said: 'I'm very conscious about making generic statements, because this ranges from farms that are completely unaffected to those who have had a complete disaster.

'We're saying that the national loss is 2.7pc and that is there in black and white in the report, so in national terms it is significant.

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'If you live in one of the counties that was comparably less affected, like Norfolk, then in general terms it may not seem too serious – but if you are one of the farms that has been affected it will be devastating.'

Mr Isaac said the regional variation could be attributed to several possible factors, but drilling time was an important one.

Across the majority of counties, the view was that the earlier WOSR was drilled, the less susceptible it was to CSFB.

It was reported that crops drilled in mid-August tended to have developed beyond the susceptible growth stage by the time the adult beetle migration started. Some of the later September drilled crops were also mostly unaffected, possibly because the number of adult beetles migrating had died.

Another cause of variation in CSFB damage could be due to resistance to pyrethroid insecticides. On a national scale, it was estimated that 58pc of the WOSR crop had been treated with at least one pyrethroid spray. In Suffolk, the report says there were typically three applications used so far, compared to one in Norfolk.

The report's estimates were based on 32,000ha of WOSR walked by members of the ADAS environmental consultancy network, which comprised 23 county-level agronomists covering 30 counties. The area walked was equivalent to 5pc of the national area, and was scaled up to give a national picture.

Mr Isaac said: 'We cannot scrutinise the data down to farm level, but there will probably have been people in Norfolk who will have had to re-drill whole fields.'

Have you lost oilseed rape crops due to flea beetle damage? Contact chris.hill@archant.co.uk.