A review of AHDB impact assessments following the neonicotinoid seed treatment restrictions in winter oilseed rape (version 2)

Abstract

On 1 December 2013, restrictions on the neonicotinoids, clothianidin, imidacloprid and thiamethoxam on winter oilseed rape were enforced by the European Commission. Oilseed rape is the third most widely grown crop in the UK after wheat and barley. The average annual value of the crop over the past five seasons is £804M. The area of oilseed rape production has fallen in recent years due to lower returns and higher risks such as losses from cabbage stem flea beetle.

Oilseed rape emergence coincides with cabbage stem flea beetle migration. Oilseed rape can suffer severe damage from both adult and larval forms of cabbage stem flea beetle. The pest is distributed widely throughout the UK and in the last two years an estimated 76% (2014) and 70% (2015) of the UK crop was affected by adult cabbage stem flea beetle. Population levels of the pest have been linked to weather conditions occurring at different times of the year.

Cabbage stem flea beetle control is part of an integrated pest management approach, however, there are practical implications associated with non-chemical control options and the pest has developed resistance to the currently available chemical control.

The national area of crop lost to adult cabbage stem flea beetle in autumn 2014 was estimated at 5% (equating to approximately 31,000 ha across England). Approximately 9,000 ha (1.5%) of the national area was also reported to have been replanted after being lost. A loss of 22,000 ha (3.5%) of the crop area in England is valued at approximately £23M. 62% of the national area of crop lost is estimated to have occurred in the East, valued at approximately £13M. In autumn 2015, the estimated crop loss in England was 3%. Any additional crop losses after 1 December, such as from cabbage stem flea beetle larvae, are not reported due to lack of evidence. However, results from Defra-funded research indicate that the mean cabbage stem flea beetle larvae population in England has increased since 2014.

The national average of CSFB damage exceeding control thresholds at the end of September in 2014 (9%) and at emergence (cotyledon to two leaves) in 2015 (22%) is estimated at approximately 15.5%. This likely to be a conservative estimate as the 2014 assessments were made at a snapshot in time at the end of September when 32% of the crop had grown past the susceptible growth stage and was not assessed.

The Eastern region of the country has been identified as an area consistently suffering from adult CSFB and larvae. Bedfordshire, Cambridgeshire, Essex, Hertfordshire and Suffolk are counties consistently being reported to have high levels of adult CSFB or larvae.

Additionally, the 2014 AHDB Winter Planting Survey reported that theoretically approximately 38,000 ha of additional winter oilseed rape may have been planted if neonicotinoids had not been restricted. The largest proportions of this additional area would have been planted in the East and South East of England.