Cabbage Stem Flea Beetle Live Incidence and Severity Monitoring Autumn 2016 and Spring 2017

Abstract

Autumn 2016 was the third year where neonicotinoid seed treatments were not available for use on oilseed rape crops (although in 2015 there was a derogation allowing use on high risk crops in part of the Eastern region). In order to understand the levels of cabbage stem flea beetle (CSFB; Psylliodes chrysocephala) damage in oilseed rape crops, a live monitoring survey of adult CSFB damage was conducted in 34 counties across England and Scotland, no data were provided for Wales as the winter oilseed rape area was very low. This is the third such survey, with previous surveys conducted in autumn 2014 and autumn 2015. Data for the survey were collected using a network of Association of Independent Crop Consultants (AICC) agronomists, and each agronomist was provided with a questionnaire template based on the CSFB treatment thresholds set out by AHDB Cereals & Oilseeds in Information Sheet 55. Agronomists were asked to report oilseed rape crop damage and loss as a result of CSFB once 75% of their crops had reached the cotyledon- two leaf growth stage (assessment 1),again when 75% were at the three-four leaf growth stages (assessment 2) and in the spring to account for over winter losses (assessment 3). A total of 48,700 ha of oilseed rape was assessed in this survey, which equates to about 8% of the forecast UK winter oilseed rape area for 2016/17. At assessment 1 there were 29% of assessed crops that had damage levels that exceeded the spray threshold (25% of leaf lost), whilst at assessment 2 there were 6% of assessed crops that had damage levels exceeding the spray threshold (50% leaf lost). At the end of assessment 3, it was estimated that 1.2% of assessed crops did not survive the winter due to CSFB damage, with an additional 2.6% of assessed crops not surviving the winter due to other causes such as dry soils and slugs.

Autumn 2016 had below average rainfall in most regions with parts of the Eastern region in particular suffering from high soil moisture deficits. The dry soils meant that where oilseed rape crops were planted, a proportion (approximately 2-3%) failed to germinate, and those that did were often slow to grow and therefore were susceptible to grazing from CSFB and slugs. It is estimated that by the end of the assessment period 3 (end of March) 4,200 ha of winter oilseed rape crops in the assessment area had failed due to CSFB (9% of the assessed planted area) with a further 4,400 ha lost due to other causes (slugs, dry soils during establishment, pigeons and waterlogging). Of the crops that were lost, 57% of these crops failed prior to assessment 1, with an additional 21% failing before assessment 2 with the remainder failing over winter prior to assessment 3. When weighted and scaled up to the national area it is estimated that 5.4% (equivalent to an estimated 31,000 ha) of the crop area was lost to CSFB damage, with a further 9.4% of the area lost to other causes including slugs and dry soils. In 2016, the main areas of crop loss (counties which lost >15% of assessed crops due to CSFB damage) were in Bedfordshire/Hertfordshire, Buckinghamshire, Northamptonshire and Cambridgeshire.