Crop Watch: look out for pollen beetle in oilseed rape

As more oilseed rape starts to flower across the country, FWi’s agronomists have urged growers to closely monitor crops for signs of pollen beetle.

Pollen beetle numbers are increasing in the warmer spring weather to around 3-5 per plant, but have not yet reached threshold levels,” James Boswell from HL Hutchinson in Kent said.

“Backward pest-affected fields will need very close monitoring as they will be vulnerable for much longer.”

In Gloucestershire, Neil Donkin said forward oilseed rape crops were starting to flower, but most were still at, or approaching green bud stage. “Do keep monitoring crops as they are at a vulnerable stage.”

Treatment thresholds

Like other agronomists, he urged growers to only apply insecticides when treatment thresholds were reached.

UAP’s Will Foss suggested that where oilseed rape crops were starting to flower, this insecticide should be Mavrik [tau-fluvalinate] (or Biscaya [thiacloprid] where pollen beetle resistance was confirmed) to reduce the risk to any bees foraging in the flowering crop.

“Remember Mavrik is not compatible with boron.”

Crops were still a little way off flowering in East Lothian, AICC agronomist and farmer, Andrew Riddell said. “We have had cold northerly airflows for much of the past month resulting in very little crop growth.”

Forward rape was close to the green bud stage, but many pigeon-affected crops had green area indexes of less than 1.2, he said. “We still have the final split of nitrogen to be applied [to forward crops], waiting until it’s almost too high for the spinner before application.”

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