Pollen beetle March migration and pest position

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Winter may appear to be reluctant to finish its shift but, through the numerous icy blasts, signs of spring are appearing. One of these signs is the migration of pollen beetle to oilseed rape (OSR) – and an online prediction tool says conditions have been good enough for early migration to occur in some places.

Pollen beetles are interesting bugs: not only are they highly visible but they also don’t often deserve to be awarded ‘pest’ status. In recent years, in fact, pollen beetles have rarely been abundant enough to warrant treatment, even if seen at the damage-susceptible ‘green-yellow bud’ stage.

Pollen beetle resistance to pyrethroid insecticides is now widespread throughout the UK, so it makes sense to understand when an often ‘innocent’ beetle deserves to be elevated to ‘pest’ status.

Findings from an ADAS-led project, funded by AHDB over the last few years, have just been published. The conclusions help confirm where the line between ‘friend’ and ‘foe’ sits.

The main conclusion from the work was consistent with earlier findings – pollen beetle numbers are rarely damaging and current thresholds and monitoring methods provide a good basis for an integrated pest management (IPM) strategy.

By following an IPM strategy, the need for insecticide treatment will be minimised, efficacy protected and costs reduced.

The experiments conducted as part of the research also found OSR was extremely tolerant to pollen beetle damage. For example, the work showed all buds from the primary raceme could be removed with no impact on yield.

The evidence is being used to review the current threshold system but, for 2018, the current system still stands. This threshold system depends on the plant population density. Plants in low plant population crops produce more branches and flowers and pollen beetle is less of an issue – so they can tolerate a higher number of beetles.

The project also found that the Bayer Pollen Beetle Predictor (BPBP) accurately predicted the peaks of pollen beetle migration and that the tool can be used to reduce monitoring effort by around a third (compared with weekly in-field assessments).

An Oecos pollen beetle monitoring trap, baited with an attractive lure, was also found to be more effective at trapping beetles than unbaited yellow sticky traps. Such traps can be used to detect pest movement and abundance, although they have not yet been calibrated to detect threshold numbers in the crop.

As pollen beetle immigration is usually greatest on the north-east side of the field (opposite to the prevailing wind), these areas of the field should be the focus for monitoring traps and crop walking.

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