Pollen beetle migration has started across the UK, but many growers and agronomists are reporting numbers in crops are below threshold levels. Experts are advising growers not to spray unless thresholds are met.

The onset of pollen beetle migration was being reported in a number of areas this week, including Essex, Sussex, the South West and Lincolnshire.

Agrovista technical manager Mark Hemmant says: “Migration has started, but numbers are mostly below threshold at the moment. Crops will need monitoring up until early flowering.”

Bayer CropScience’s most recent pollen beetle bulletin reports good migration conditions across the southern half of England. However, the firm emphasises this does not mean beetles are entering crops, but rather beetles are emerging from hibernation.

DuPont’s live update on pollen beetle build up shows more than 11 beetles found on traps in two locations in Lincoln and another in Kings Lynn (as of March 18)

Lincolnshire-based agronomist Sean Sparling says he has not found pollen beetle numbers even close to thresholds in any of the oilseed rape he walks across Lincolnshire. “Do not spray unless you reach thresholds,” he adds.

According to Syngenta, pollen beetles are on the move just as many oilseed rape crops are growing through stem elongation and starting to bud – the time when they are most susceptible to feeding damage. Pollen beetle activity has been reported in several regions this week, says the company.

Inspect crops

Growers are being urged to inspect crops regularly for signs of beetle migration and to treat when thresholds are reached. New advice from the HGCA advocates control at lower thresholds in thick crops, which could be especially relevant this season after strong autumn growth, says Syngenta oilseed rape manager Gary Jobling.

“Crops with a high plant population have less ability to branch out and compensate for the pollen beetle damage to buds, compared to less dense crops. They are typically the first crops to come into bud, and will therefore be under the most intense feeding pressure as the beetles search for pollen,” he says.

Once plants start to flower, the beetles are attracted to open flowers where the pollen is readily accessible. At that stage they become positive pollinators for the crop, with little or no further significant damage to remaining buds, adds Mr Jobling.

This week’s cooler and windy conditions are likely to be less favourable for migration and some crops will almost certainly be in-flower before control thresholds are reached. However, more backward crops and later flowering varieties will need monitoring, say agronomists.

Source - http://www.farmersguardian.com/