Last week’s warm weather saw cabbage stem flea beetle (CSFB) attacking recently emerged oilseed rape crops with high levels in some areas but the decision about whether to spray with pyrethroids is a difficult one.
NFU senior plant health advisor Emma Hamer, who farms near Banbury, Oxfordshire, says last year she intended to avoid spraying but ended up doing so because the risk was too high but this year she has avoided spraying so far. “We had rain one night and when I looked at it the next day it seemed to be growing away from it.”
She says making the decision to spray or not is not easy. “There is conflicting advice. Do you hold your nerve and not spray against it but agronomists do not want to see crop failure.”
Ben Burrows, independent agronomist at Crop Management Partners, covering Berkshire, Oxfordshire, Wiltshire and Hampshire says he was optimistic 2-3 weeks ago about oilseed rape crops growing away from CSFB. “We were hopeful the moisture would be sufficient to get crops going quickly but the weather changed and it became warm and dry again, ideal for the flea beetle and crops slowed down.”
He says he has seen a lot of CSFB in the last week (ending September 14) but some crops are untouched. “In some cases this is sheer luck, in others there is something helping. The ones doing ok tend to have been direct drilled where there has been less soil disturbance or where digestate or sewage cake has been applied – perhaps it is masking the smell of the oilseed rape?”
Where CSFB is a problem, some growers are testing whether it is resistant to pyrethroids before deciding to spray, says Mr Burrows. “On others, we are making one application with no more after that.”
With growers aware that there could be a problem with CSFB, strategies such as growing less oilseed rape, not using a pre-em and using home-saved seed are being used to mitigate the risk, says Mr Burrows.
Significant numbers of growers and agronomists took to Twitter to vent their frustration over CSFB numbers and share pictures of oilseed rape crops damaged by the beetle. One described CSFB pressure as ‘unreal’.