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17,000ha of winter OSR lost to flea beetle damage

Around 17,000 hectares of winter oilseed rape crops have been lost due to damage from cabbage stem flea beetle (CSFB), according to an assessment commissioned by HGCA.
Flea beetle has caused heavy losses in southern and eastern England
Flea beetle has caused heavy losses in southern and eastern England

In the first autumn without neonicotinoid seed treatments, flea beetle damage has contributed to estimated losses of 3.2 per cent of the winter OSR crop across England and Scotland. But this masks significant regional variation with some growers experiencing ‘significant control issues’ particularly in southern and eastern England.

 

This was particularly the case in Hampshire, where 46 per cent of winter OSR was reported as having damage levels at or above treatment thresholds, Bedfordshire (43 per cent) and Hertfordshire (43 per cent).

 

Of the overall area lost, half of the estimated area had been re-drilled and half currently left bare.

 

The assessment, carried out by ADAS, covered the period September 22 to 29 but the regional picture of growth stages and treatment thresholds meant further crop losses could not be ruled out, HGCA said.

 

The NFU has repeatedly warned that the EU suspension of neonicotinoid seed treatments has exposed the industry to potentially serious losses from flea beetle.

 

It has cited a number of examples where individual farmers have suffered heavy losses and warned that the ban could be counterproductive if it results in less OSR, a vital crop for bees, being grown in future.

 

Speaking at the Conservative Party Conference this week, NFU vice president Guy Smith said: “It is quite clear the Commission had no idea what would happen to the ability of farmers to produce OSR if they banned neonics and that is now being writ large over thousands of acres in eastern England.”

 

HGCA research manager Caroline Nicholls said HGCA commissioned the assessment in response to anecdotal reports of CSFB damage over the early autumn.

Main findings

Estimates were based on 32,000ha of winter OSR walked by members of the ADAS network, equivalent to 6 per cent of the national area. No data was included from Wales which accounts for 1 per cent of the Britain’s winter OSR area.

 

The key findings include:

 

  • It was estimated that 55.4 per cent of the winter OSR area had either grown past the susceptible growth stages (34.9 per cent) where adult CSFB causes the most damage or was currently unaffected by CSFB (20.5 per cent).
  • Further crop losses could be anticipated as the report also estimated that 41.4 per cent of currently affected winter OSR was still at a growth stage considered vulnerable to CSFB damage.
  • Of these crops, 7.5 per cent were considered to have already sustained damage above the control thresholds.
  • In most counties, the view was that the earlier the crop was drilled the less susceptible it was to CSFB.
  • 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 decreased.
  • It is too early to assess the impact of CSFB damage on yield.

Pyrethroid resistance

It was estimated that, nationally 59 per cent of the winter OSR crop had been treated with at least one pyrethroid spray. But where there was severe damage, such as in the South East and Eastern counties, repeat spray applications were more common.

 

HGCA suggested another cause of variation in CSFB damage could be due to resistance to pyrethroid insecticides in CSFB.

 

In September, HGCA confirmed that resistance to pyrethroids in CSFB was widespread, based on positive test results from all six counties tested.

 

Defra recently agreed to an Emergency Authorisation, until January 23, of InSyst (acetamiprid) for use in winter OSR against CSFB.

 

HGCA said this would give growers ‘crucial spraying flexibility and will play an important part in the management of pyrethroid resistance’.

 

However, only one autumn foliar application of any neonicotinoid insecticide is permitted.


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