Oilseed rape growers in East Anglia have been urged to join this winter's research efforts to find non-chemical ways to control a destructive crop pest.
The Innovative Farmers field lab has been extended for a second year amid growing concern over the damage caused by cabbage stem flea beetles.
The pest was previously controlled using neonicotinoid seed treatments, now banned due to concerns over their impact on bee health, and there is widespread resistance to the foliar pyrethroid sprays used as an alternative.
The farmer-led research project involves defoliating crops - using sheep, mowing or topping - before the end of January to tackle the beetles during their larval stage.
In the first year, farmers who defoliated crops in winter 2018-19 saw an average larval reduction of 39pc in spring - but for many this was followed by an overall reduction in crop yield at harvest.
However, initial plot trials with agricultural consultancy ADAS showed small increases with December and January defoliations, suggesting timing is key to give the crop enough time to bounce back.
Another farmer reported a reduction in yield was down to allowing sheep to graze for too long, and where grazing was restricted and done earlier the crop responded better but still saw the crucial reduction in larvae.
Norfolk triallist Chris Eglington, who farms at Letton, near Shipdham, said: "The grazed plot produced a much lower yield than had been expected compared with the rest of the field, but I'm keen to try defoliation again.
"I have already grazed another plot of oilseed rape in early November to see if earlier grazing will have a positive effect on yield. One bonus of the grazing is that it acted as an excellent charlock control so I'm interested to see if I can get a similar effect again next year and getting data from your own farm rather than others is invaluable."
With funding from Cereals and Oilseeds branch of the AHDB (Agriculture and Horticulture Development Board) and chemical firm BASF, the second year of the not-for-profit project will test the timing theory in real farm settings, as well as assessing any variation in results due to weather.
Dr Sacha White, senior research entomologist at ADAS, is looking for farmers able to attempt defoliation in December or January.
He said: "The yield results from year one of the research were disappointing but we believe this is down to timing as the crops didn't have time to recover, rather than being down to the method itself.
"It could also be in part due to the weather as the mild winter conditions may not have killed off larvae and poor spring conditions may have limited crop recovery.
"This year, many early sown crops have survived adult flea beetle feeding but are likely to have high larval loads and so defoliation may be ideal for these crops. With farmers dealing with devastation caused by this pest and no effective control available, it is crucial that we explore the factors that can impact on potential solutions and that the research takes place on real farms with real farmers."
Anyone growing winter oilseed rape can get involved in the field lab and will be able to choose the defoliation method that best suits their farm.
- To get involved or find out more contact Sacha.White@adas.co.uk or visit the Innovative Farmers website.
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