A Norfolk farm experiment has shown that grazing sheep on arable fields can help kill off a destructive beetle pest – but unfortunately they also ruined the crop in the process.
Chris Eglington, who farms at Letton, near Shipdham, is one of the triallists in the Innovative Farmers field lab project, exploring non-chemical ways to reduce the damage caused by cabbage stem flea beetles to oilseed rape.
The pest was previously controlled using neonicotinoid seed treatments, chemicals now banned due to concerns over their impact on bee health.
Mr Eglington’s experiment involved using sheep to defoliate a 1.4-hectare plot of oilseed rape during a seven-day period in early November, with the idea that removing the leafy food source during the larval stage would reduce the numbers of adult beetles able to attack the plants when they re-grew – hopefully with a positive eventual effect on the yield.
The strategy did succeed in significantly reducing the numbers of beetle larvae, as well as destroying troublesome charlock weeds.
However, the wet winter weather conditions affected the plants’ ability to bounce back and the grazed area is only now coming into flower, three weeks behind the rest of Mr Eglington’s oilseed rape – meaning 35pc of the trial crop “won’t make it to harvest”.
Nevertheless, he said valuable lessons had been learned from this second year of this trial.
“I think the problem we have had this year is that we grazed it really hard and it was awful weather so the plants never got going,” he said.
“After the first year I thought the only reason we had not got a good re-growth was because we grazed in January and not earlier. That trial plot was a tonne per hectare down on the rest of the field, which is considerable.
“This year we did graze it earlier, wanting to rake advantage of the chance to get rid of charlock, but this season was completely different to last year’s in that it was so wet and miserable.
READ MORE: Huge £120m tomato greenhouses will make East Anglia a beacon for low-carbon farming“One of the things I have done wrong is to graze it too hard. It was wet all the time the sheep were on there, and I think we should have taken them off earlier. If we had a lovely dry, mild autumn I think the crop would have got going, it may not have been that much further behind and we would have had the advantage of getting rid of the flea beetle, so it may well have seen a yield increase – but we have just not had the season for it.”
Mr Eglington said the experiment achieved its goal of reducing the numbers of beetle larvae, with researchers from agricultural consultancy and project partner ADAS finding an average of 13 and seven larvae per plant on the two grazed areas, compared to a “quite frightening” 55 per plant in the main field.
“Getting rid of the charlock was also a plus, but whether it outweighs the minuses, I don’t know,” he added. “At the moment, my feeling is that the best way to get rid of cabbage stem flea beetle is to drill as early as you possibly can to give the crop the chance to get going early enough so when the flea beetle attack it, it is big and strong enough to survive – and then you will have a decent crop going into the winter.”
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