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Pollen beetle - to spray or not to spray

Innovation Centres
30.03.2017
North
East
West

Variety – Various

Growth Stage – Green/Yellow bud

Date – 30/03/17

Pollen Beetle found at Rougham and Newark. Below threshold levels at Newark, but Rougham had some plants with ~20 beetles - a high pressure in the East. Warwick innovation site had no pollen beetle visible.

Pollen beetle are a common pest of oilseed rape in the UK.  The beetles have a metallic appearance which can appear a greenish-black and clubbed antennae (AHDB, 2016). They attack in the spring and crops are most susceptible to damage during the green to yellow bud stage. Damage can result in bud abortion and reduced pod set, inevitably having an adverse effect on yield. Once the crop is fully in flower they become a beneficiary, thus application timing is vital.

The earlier flowering plants will attract beetles to the fields and feed on the remaining buds on the less advanced plants. To reduce risk, choose varieties with short and even flowering periods. The beetles are most likely to attack during periods of warmer, dry weather (above 15°C).

New thresholds have now been introduced and are supported by AHDB. These are determined by the number of plants per square metre. Crops with a lower plant density are able to compensate better as they produce more branches, thus the application threshold is much higher.

Thresholds:

– If there are fewer than 30 plants/m2 the threshold is 25 pollen beetles per plant
– If there are 30–50 plants/m2 the threshold is 18 pollen beetles per plant
– If there are 50–70 plants/m2 the threshold is 11 pollen beetles per plant
– If there are more than 70 plants/m2 the threshold is 7 pollen beetles per plant

Pollen beetle resistance to pyrethroid insecticides is now widespread throughout the UK. Consider PLENUM as an alternative to pyrethroids. To limit the spread of resistance and any impacts on non-target pollinators, only look to control pollen beetle during the green/yellow bud stages.