Suffolk oilseed rape growers ‘worst hit’ by ban on neonicotinoids, says survey

Cabbage stem flea beetle feeding on oilseed rape.
Picture: Dewar Crop Protection

Cabbage stem flea beetle feeding on oilseed rape. Picture: Dewar Crop Protection - Credit: Archant

The full cost to farmers of the neonicotinoid ban in 2016 was £18.4m and resulted in almost 28,800ha of lost crop – with Suffolk the county worst affected – according to a study funded by Rural Business Research and the Institute of Agri-Food Research.

Nationally, around 5% of the winter oilseed rape area was lost to cabbage stem flea beetle (CSFB) last year, up from the 3% loss suggested by a similar survey in 2015, with the figure as high as 16% in Suffolk.

The latest survey also suggests an increase in the use of alternative pesticides as farmers tried to control CSFB, with growers in the Derogation Area who had access to neonicotinoid treated seed using 75% less chemicals to control CSFB than those who used non-neonicotinoid treated seed.

The total estimated impact includes the cost of buying and applying additional chemicals, redrilling and the total loss of some crops.

Paul Bilsborrow, co-author of the report,said that even where the problem of CSFB did not result in crop failure and re-drilling it was still likely to have had an impact on yield.

Across the country, 72% of farms used insecticides to treat CSFB, the most common being pyrethroids and pyridine azomethine. 136,600 litres of chemicals were used nationally to combat CSFB, adding up to a total 17,500kg of active substance.

The chemicals alone cost £4.3m and the cost of applying the insecticides was estimated at a further £8.5m. Where crops were lost and not re-drilled the bill nationally was £2.9m and the cost of re-drilling crops destroyed by CSFB totalled £2.6m across the country.

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The study compared insecticide use and crop damage on farms both inside and outside of the Derogation Area, although the authors acknowledge that sample numbers were small.

The farms within the Derogation Area (DA) that used treated seed used four times less pesticide than those inside the DA without treated seed. The rate of pesticide use with neonicotinoid treated seed was just 0.01kg per ha of active substance, compared to 0.04kg per ha on crops with non-neonicotinoid treated seed.

Charles Scott, the report’s other co-author, said: “The area of WOSR in the UK fell for the fourth consecutive year in 2016, from a peak of 756,000ha in 2012 to just 597,000 ha in 2016.

“Amongst participants in the study, CSFB was among a range of factors cited for farmer’s reducing their OSR area, including rotational position and price pressures.”

Where higher levels of insecticide were applied, levels of CSFB damage were lower, says Dr Bilsborrow. Lincolnshire had one of the highest rates of application, accounting for 24% of insecticide use nationally, but suffered one of the lowest proportions of crop losses from CSFB, at just 3%.

“Chemicals are clearly a vital weapon in the battle against CSFB but our study also shows farmers are utilising a range of cultural strategies to combat the pest. Nationally 42% of OSR growers changed drilling dates and within the DA 61% of farmers opted to drill earlier, a further 11% increased seed rates and 19% increased spray applications.”

Of the farms that were surveyed 26% reported damage greater than in the previous year and only 13% reported less. “The ban is obviously having a major impact on the viability of OSR in England,” added Mr Scott. “Without access to treated seed in the high risk areas, especially in Eastern England for 2017, it’s possible that CSFB damage will be even greater this year.”