Yellow peril for farmers

C&I Issue 10, 2014

What could be more quintessentially English than golden yellow fields of oilseed rape? Yet picture the scene if they were suddenly to be stripped bare and simply left to lie fallow. Unthinkable? Yet some farming experts fear this is what could happen following the recent EU-wide ban on neonicotinoid seed treatments linked to sudden losses of honey bees in the US and Europe.

They argue the ban could do more harm than good by removing a valuable source of nectar and pollen for bees in early spring when oil seed rape (OSR) is one of the few plants that flowers abundantly.

Already, according to Bayer Crop Science’s Julian Little, there are reports that planting of OSR seeds is down 10-20% in 2014: a figure confirmed by the UK National Farmers Union (NFU). The news comes alongside reports of a dramatic spike in resistance of a major OSR pest, cabbage stem flea beetle (CSFB), to pyrethroids – the main alternative insecticide to neonicotinoids. A pre-harvest survey by researchers at Rothamsted Research ‘found kdr pyrethroid-resistant beetles in all samples tested so far,’ says Caroline Nichols of crop research organisation HGCA, which funded the research. ‘The data confirm that resistance is widespread.’

According to HGCA data, around 67% of the UK’s OSR acreage is currently affected by the pest. And there are fears that greater use of pyrethroids as a result of the restrictions – ‘already seen this season’, says Little – will only accelerate the resistance problems.

‘What’s worrying is that from only being suspected resistance in CSFB last year this is now so prevalent,’ says the NFU’s Guy Gagen. ‘Farmers won’t stop growing OSR overnight but what we are likely to see is a progressive reduction as farmers are no longer willing to take the risk to grow it.’

Instead of growing OSR, he warns that ‘illogical’ new rules governing CAP rotation due to start 15 January 2015 could actually ‘encourage farmers to grow nothing’. In the UK, OSR seed is sown from 10 August to around 10 September, Gagen explains, while crops are vulnerable to attack from CSFB as soon as they germinate in soil.

But ‘CSFB is just the start of the problems,’ says Linda Field at Rothamsted. ‘Later will come aphids, which carry plant viruses that affect the plant’s growth.’ According to HGCA, 60% of the UK’s OSR acreage is affected by Turnip Yellows virus (TuYV); without insecticides, annual tonnage lost is 206,010t, ca £67m/year.

‘TuYV can devastate a crop of OSR and even in good years will reduce the yield by 15-30%,’ says Little. ‘This is by far the biggest threat to farmers because the aphids are resistant to pyrethroids.’

Syngenta’s pymetrozine foliar spray products are effective against aphids, Gagen notes, but can only be sprayed once, which makes them of little use if aphid attack is prolonged or there is more than one attack; other products are approved but only for use as flowering starts in spring – largely because the manufacturers did not originally foresee a market for them at this time of year. Meanwhile, some farmers are importing seeds from France treated with Mesurol (methiocarb), which persists for only 14 days compared with the six to eight week protection conferred by neonicotinoids.

Longer term, Little says BCS is ‘hopeful of getting an authorisation for use of thiacloprid to control pyrethroid-resistant aphids; this is a third generation neonic [spray] with an intrinsically low bee toxicity profile’.

Strictly speaking, the ‘ban’ on neonicotinoids is a restriction as some neonicotinoid products, for use in sugar beet, for example, are still permissible. It took effect from December 2013 and affects imidacloprid, clothianidin and thiamethoxam used in seed treatments for OSR, maize and sunflowers.

According to Vanessa Amaral-Rogers at BugLife, one of the main groups lobbying for the ban: ‘The theory behind these pesticides being used as a seed treatment is sound. They use a smaller amount of chemical as they should be more targeted. The problem is that because they are systemic, they end up in the nectar and pollen, which then affects pollinators. They are also using it as a prophylactic. We would compare it to taking an antibiotic on the off chance you are going to get ill.’

However, opponents of the ban disagree and point out that neonicotinoids are only one of many factors, including the Varroa mite, viruses, adverse weather and low biodiversity, implicated in honey bee losses. ‘I seriously doubt one can solve the problem by a ban on neonics alone,’ says Field, pointing to healthy bee populations in Australia where neonicotinoids continue to be used without restrictions.

‘Delivery of insecticide through the seed is a good approach,’ Field continues. ‘If sprays are used instead there is greater potential for contamination of non-target species.’

This view is echoed by Little, who warns that ‘pyrethroids kill significantly more insects than a seed treatment, which only kill insects eating the plants. And less insects equals potentially less insect food in the spring for other animals and birds’.

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