Scottish winter oilseed rape cultivation 2015-2016: impact of the second year of neonicotinoid seed treatment restrictions

Executive summary

This is the second of two consecutive surveys, conducted to inform the Scottish Government, about the impact of the current neonicotinoid restrictions on Scottish winter oilseed rape ( WOSR) cultivation. Data were collected from a representative sample of Scottish growers collectively accounting for 18 per cent of the 2016 WOSR crop area.

2016 was a difficult year for Scottish WOSR cultivation. There was a 14 per cent decrease in Scottish crop area and a 20 per cent reduction in yield; both of which were primarily attributed to adverse weather conditions. However, autumn insect pest populations, which were formerly controlled by neonicotinoid seed treatments, were also significantly lower than in the previous year. As a consequence, insect damage levels, primarily from Cabbage Stem Flea Beetle ( CSFB) grazing, were significantly reduced and, unlike autumn 2014, no CSFB-related crop loss was reported. The proportion of crops with symptoms of Turnips Yellow Virus ( TuYV), which is transmitted by aphids, also continued to be low in 2016.

In response to reduced pest and damage levels, significantly fewer insecticidal sprays were applied by Scottish growers in autumn 2015 than in the previous year; and the number of foliar applications was similar to pre‑restriction levels. As in the previous survey, the insecticides used were almost exclusively pyrethroid compounds, targeted at CSFB control, and few growers reported issues with the efficacy of their pest control strategies.

Despite it being a sub-optimal year for Scottish WOSR production, this survey corroborates the findings of the previous survey. The neonicotinoid restrictions have introduced additional challenges for some Scottish WOSR growers. Despite low damage levels, more than a third of growers still felt that the lack of an insecticidal seed treatment had led to greater crop damage, and a small proportion of growers stated that the restrictions will reduce the likelihood of their growing WOSR in future. However, other growers appear to be relatively unaffected and it is clear that the impact of the restrictions is less severe in Scotland than in other regions of the UK.

This reduced comparative impact is influenced by lower pest pressure and resistance levels to the approved foliar insecticides available; both of which may change in future. However, in the interim, it appears that Scottish growers can, on the whole, continue to successfully cultivate WOSR during the moratorium on neonicotinoid use. At a UK level, new research and guidance about alternative control strategies is being formulated. This will determine which actions are best adopted in future integrated pest management ( IPM) strategies for oilseed rape.

No follow up surveys on Scottish WOSR crop cultivation are scheduled. However, this position will be reassessed if evidence suggests further monitoring is necessary.

Introduction

This is the second of two surveys conducted by Science and Advice for Scottish Agriculture ( SASA). These surveys are designed to inform the Scottish Government about the impact of the EU restrictions of neonicotinoid use on Scottish winter oilseed rape ( WOSR) cultivation.

In December 2013, the European Commission amended the approval conditions for three neonicotinoid insecticides; clothianidin, imidacloprid and thiamethoxam ⁽¹⁾ . These restrictions were imposed in response to a series of scientific reviews by the European Food Safety Authority ( EFSA), which concluded that there was insufficient information to fully describe the risk to pollinators resulting from exposure to these compounds ^(2)(3)(4) . The EFSA reviews are being updated to reflect new scientific information, and this work is scheduled to be finalised in autumn 2017. This will inform the European Commission position on the future approval of these compounds.

In the UK, the main impact of these restrictions is the loss of insecticidal seed treatments for oilseed rape. In Scotland, oilseed rape crops currently consist mainly of winter sown varieties, with spring crops accounting for around two per cent of crop area ⁽⁵⁾⁽⁶⁾ . WOSR is Scotland's principal break crop in arable rotations, providing an alternative cropping system to help suppress the build-up of weeds, disease and insect pests associated with cereals and potatoes. It is also an important component of Scotland's agricultural economy. The Scottish oilseed rape crop had a market value of £37.1 million in 2015 ⁽⁷⁾ .

As discussed in the first report in this series, WOSR is host to a wide range of insect pests and this is reflected in greater foliar insecticide input than other combinable crops ⁽⁸⁾⁽⁹⁾ . In addition to sprays, use of insecticidal seed treatments, to protect crops from insect damage during emergence and establishment, has previously been an integral component of oilseed rape production. Neonicotinoid seed treatments have been approved on UK WOSR crops since 2000 and around 80 per cent of Scottish crops were grown from treated seed before the onset of the current restrictions ⁽⁹⁾ . Prior to the advent of neonicotinoid seed treatments, Scottish crops were treated with lindane (Gamma- HCH), an organochlorine insecticide which lost approval in 2001 ⁽⁹⁾ .

In Scotland, the main autumn insect pests of WOSR are cabbage stem flea beetle ( CSFB, Psylliodes chrysocephala), the peach potato aphid ( Myzus persicae) which transmits turnips yellow virus ( TuYV) and, to a lesser extent, Phyllotreta spp. flea beetles ( Phyllotreta cruciferae and Phyllotreta nigripes). In the absence of an insecticidal seed treatment, control of these pests is reliant on foliar insecticide application. The other main autumn pest is the rape winter stem weevil ( Ceutorhynchus picitarsis), which invades the crop later in the season, after the period in which neonicotinoid seed treatments provide protection from phytophagous insects.

There are operational limitations associated with foliar use of insecticides ⁽⁸⁾ , and control options are also limited by the development of resistance by the target pests to many of the approved insecticides ^(10)(11) . These issues have been recognised by the UK regulatory authority and emergency and extension of use authorisations have been made to allow some alternative foliar insecticides to be available for autumn use. In addition, an emergency authorisation was granted to allow the use of two neonicotinoid seed treatments (thiamethoxam and clothianidin) on a limited area of oilseed rape in autumn 2015. This authorisation was approved for those areas at highest risk of crop loss (ca. 30,000 ha, five per cent of England's oilseed rape crop) ⁽¹²⁾ . No emergency authorisation application was made for use of neonicotinoid seed treatments in Scotland.

During the first year of the restrictions, SASA conducted a survey to gather information about the initial impact on Scottish WOSR cultivation ^f8) . The results indicated that the absence of neonicotinoid seed treatments made the control of autumn insect pests more challenging for some growers but the overall impact of the restrictions was less severe in Scotland than was reported in Southern and Eastern England. A second season of data collection was undertaken to assess the impact of the restrictions under different, potentially more challenging, conditions. This report describes the results of this second survey.