Almost half the country is nearing the start of the pollen beetle season and oilseed rape growers are being urged to check their regional forecast.

Over the last week, a further 30 of the met stations on the migration start map have turned red.

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Bayer’s Agri Services manager Nathan Whitehouse advises: “If your nearest met station has turned red, it’s time to start keeping a daily watch on the ‘new migration’ and ‘percent migration’ maps.

“We’re at the point where it will only take a couple of proper spring days with temperatures warming to 15C to get the pollen beetle season under way in earnest.”

Pollen beetle attacks can lead to lower yields, as they feed from green- to yellow-bud stage prior to flowering.

However, HGCA is reminding growers of last year’s changes to the spraying thresholds, which are now based on plant populations. This is to avoid unnecessary treatments and help with pyrethroid resistance management.

Caroline Nicholls, HGCA research and knowledge transfer manager, explains: “Based on experience in recent years, pollen beetles have rarely been numerous enough to warrant treatment.

“By using thresholds to prevent ‘insurance’ sprays and following resistance management advice, such as not spraying after flowering starts, we should be in a good position to get on top of the resistance threat, which is now widespread throughout the UK, without compromising control.”

She says that plants in low plant population crops produce more branches and flowers and can tolerate a higher number of pollen beetles. Grower can estimate the number of plants/sq m by counting the number within a square foot and multiplying by 11.

The current thresholds are as follows:

• If there are fewer than 30 plants/sq m, the threshold is 25 pollen beetles/plant
• If there are 30-50 plants/sq m, the threshold is 18 pollen beetles/plant
• If there are 50-70 plants/sq m, the threshold is 11 pollen beetles/plant
• If there are more than 70 plants/sq m, the threshold is seven pollen beetles/plant

See the current forecast to check whether the migration has started in your region.