As pollen beetles move off the winter crop at the end of flowering, they will be making a beeline for spring oilseed rape crops, where green-yellow bud is the key risk timing. One pollen beetle per plant can often cause enough damage to reduce yield. Check spring rape crops regularly until the onset of flowering and apply an insecticide if more than one beetle per plant is found throughout the crop.
Resistance in pollen beetles to pyrethroid insecticides is present in Scotland. The advice to growers is that pyrethroid insecticide use for pollen beetle control should only be used if the treatment threshold of one beetle per plant at green-yellow bud has been exceeded. Do not apply a pyrethroid insecticide to flowering oilseed rape for pollen beetle control – it is not needed as the beetles can get to the pollen without damaging the crop. If control is really necessary, only use one pyrethroid insecticide treatment per crop which will control any pyrethroid-resistant beetles.
If there is any suspicion that you may have pyrethroid insecticide-resistant beetles because of poor control, contact your agronomist who can arrange for beetles from that crop to be tested to help with a national profile of how widespread resistance of pyrethroids may be.
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