Analysis: Farmers say flea beetle damage worse than AHDB figures suggest

Autumn flea beetle damage to oilseed rape crops appears to be less severe this season – although if you look at the wider picture there is a strong argument that it is actually getting worse.

An AHDB survey of cabbage flea beetle damage showed 1% of the crop was lost to the pest last autumn, compared with 2.7% the previous season. But that’s not the full picture.

With the rapeseed area down 14% this season – and 5% of that reduced crop area protected by neonicotinoid seed treatments – the pest problems might be getting worse, rather than better.

Problem spreading

The four “hotspot” flea beetle counties of Suffolk, Cambridge­shire, Bedfordshire and Hertfordshire were able to use neonicotinoids this season to cover 30,000ha, but the problem is spreading wider into Buckinghamshire, Yorkshire, Lincolnshire and Northamptonshire.

The emergency use of neonicotinoid seed dressing in these hotspots gave many growers the assurance to stay with OSR, although many cut their areas sharply.

Growers moved to counter the flea beetle threat by earlier drilling, choosing varieties with vigorous early growth and moving to wider rotation, but there is still plenty of damage.

See also: Weather conditions see flea beetle activity surge in oilseed rape

The weather was a blessing last autumn as a mix of rain and sun saw crops out of the ground and growing rapidly before the flea beetle migration began in mid-September.

In autumn 2014, we had a dry autumn – which meant slow growth and a short, intense migration period and bad flea beetle damage. So who is to say autumn 2016 will not be dry again?

Many agronomists were a little surprised at the high level of damage this autumn, given the early drilling and good growing weather, so this pest problem is not about to disappear overnight.

The area of rapeseed is down for the fourth season in a row – to about 565,000ha – partially due to flea beetle damage putting a question mark over the future of this valuable break crop.

There is likely to be a strong call for another emergency use of neonicotinoids this autumn, while the regulators will no doubt be keen to have a tighter targeting of its use.

European scientists are currently reviewing the three neonicotinoid chemicals used in seed dressings – thiamethoxam, imidacloprid and clothianidin – which were banned in December 2013, but are not expected to report back until January 2017.

Bee health

Environmental groups argue that there is overwhelming evidence linking neonicotinoids to a decline in bee health, which was the primary factor behind the ban in the first place.

A full-scale return of neonicotinoids is unlikely to happen this summer, and there must be growing doubts whether these insecticides will ever fully return.

Growers are doing their best at limiting damage by all the agronomic means at their disposal, but what is needed is a renewed effort to decide on any harmful effects of neonicotinoids and whether there are any alternatives.

Efforts to bring in a non-neonicotinoid alternative failed to convince regulators last year, but this is an urgent problem and an answer is needed quickly – or the area of rapeseed will fall again.

Growing rapeseed in the beetle hotspot

Hertfordshire grower Andrew Watts has halved his oilseed rape area this season, after losing one-fifth of his crop last year within the hotspot area for flea beetles.

Last summer, he drilled his rapeseed a few days earlier and applied some seed-bed nitrogen fertiliser to get the oilseed rape off to a good start, as establishment is often key to a successful crop.

“Crops are much better placed this season. There is some shot holing on leaves, but the situation is certainly much better that last season,” said the former chairman of the NFU’s combinable crops board.

Growing the crop is now a big risk for Mr Watts – as well as losing 20% of his crop in autumn 2014, the rest of the crop was down 1t/ha in yield by harvest in 2015.

Many of his neighbours have cut back on rapeseed, and growing the crop now comes with a big risk, even though Mr Watts is growing the break crop in a relatively wide rotation of one in five.

“It is vital that we have a reliable method of controlling flea beetle. If not neonicotinoids, then we need another solution,” he said.

Neonicotinoid ban damages OSR yields

The loss of neonicotinoids is having a crippling effect on oilseed rape crops in areas plagued by flea beetle, says Suffolk farm manager Steven Offord.

Average yields at Mr Offord’s Clopton Green Farm, near Rattlesden, were down from 5t/ha in 2014 to 4.75t/ha last year.

Mr Offord believes the AHDB figures of 1% fail to tell the whole story about what is really happening in the field.

This year, he is growing two conventional varieties treated with a neonic insecticide seed treatment, alongside an untreated hybrid variety.

“To begin with, there was a bit of a lull with flea beetle. But the crop came up and they came with a vengeance,” he said.

“We have got flea beetle larvae everywhere in the plant. My gut feeling is that we will find larvae even in neonicotinoid-treated rape.”

Mr Offord is concerned about what a future without neonics might hold.

“The truth is, if we are spraying with pyrethroids, we are going to end up with a massive resistance population. It’s going to have a worse effect as the years go by.”

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