About 6,000 hectares of winter oilseed rape (WOSR) was lost as a result of adult cabbage stem flea beetle activity across the UK in autumn 2015, according to a survey by AHDB Cereals and Oilseeds.
In the second planting season without access to neonicotinoid pesticides for most growers, the estimated losses amounted to about 1 per cent of the WOSR crop, down from 2.7 per cent in 2014, albeit with a different methodology deployed by AHDB.
But despite the reduced threat from the pest in the current crop, the case to retain neonicotinoids to protect crops remains undiminished, according to NFU and AHDB.
A total of 62,000ha, 11 per cent of the UK WOSR crop, was assessed twice by 56 AICC agronomists across 42 counties in England, Wales and Scotland, with damage estimates calculated by ADAS.
By the second assessment, after 75 per cent of crops had reached the three-four leaf growth stage:
As in 2014, crops that were drilled earlier tended to move through the vulnerable periods more quickly.
About 3.1 per cent of the WOSR area, 18,000ha, was lost due to other causes, particularly slug damage.
The NFU secured a derogation from Defra allowing limited use of neonicotinoid seed treatments in autumn 2015 on about 30,000ha across four counties in England - Suffolk, Cambridgeshire, Bedfordshire and Hertfordshire.
NFU vice president Guy Smith, insisted the survey results did not remove the need for continued access to the chemicals, which he described as ‘insurance’ for farmers.
“There is clearly an element of insurance as when the farmer puts the seed in the ground he doesn’t know whether or not he is going to have a patchy germination window.
“In difficult seasons when the crop struggles grow away in the month after sowing, as was the case in 2014 in the M11 corridor, neonicotinoids become absolutely essential.
“There is an element of flea beetle pressure as well and you never know whether you are going to get those conditions.
"This year on the whole establishment conditions were pretty good and neonicotinoids were not that important.”
He said he would expect to need neonicotinoids on his Essex farm, on heavy land, ‘one year in two or three’.
He said neonicotinoids were also useful in addressing other OSR disease problems like turnip yellow virus, while in their absence farmers were increasingly using pyethroids, which was ‘encouraging resistance’ in the long-term.
“I can understand why it is difficult for non-farmers to understand why we need access to neonicotinoids in years when hindsight shows it is not necessary. But it is more complicated than that and the analysis of why we need them is correct.”
Bill Parker, AHDB’s director of research and knowledge exchange – crops, said flea beetle activity ‘will vary a lot from season which will alter the need for control’.
He said: “In 2015 activity was down on what we saw in 2014, though still significant in some areas.
“Essentially we need to maintain as wide a range of options as possible for flea beetle control, largely because pyrethroid resistance in cabbage stem flea beetle is a developing problem and we need a range of products to try and manage resistance.
“If pyrethroid resistance becomes widespread then in the absence of neonics, as things currently stand, there is very little in the way of alternatives, certainly not enough to have a meaningful resistance management strategy."
Mr Smith said the NFU was considering submitting an application for a derogation for 2016 and would need to do so by April.
But he said the NFU would like to see provisional results of ongoing work by the Centre for Ecology and Hydrology on the impacts of neonicotinoids on honeybees before deciding its next steps.
Responding on Twitter, Friends of the Earth campaigner Dave Timms said: "OSR yield up, CSFB losses down, evidence of threat to bees etc from neonics stronger than ever. Yet NFU still defends them!"