Cabbage stem flea beetle live incidence and severity monitoring 2015

Abstract

Autumn 2015 marks the second season for which neonicotinoid seed treatments have not been available for use on the vast majority of oilseed rape crops in the UK. In order to further understand the impacts of the second year of the neonicotinoid restrictions on the levels of cabbage stem flea beetle (CSFB) damage to oilseed rape crops, a live monitoring survey of adult CSFB damage was conducted in counties across England, Scotland and Wales. Data for the survey was collected using a network of 56 Association of Independent Crop Consultants (AICC) agronomists, and each agronomist was provided with a questionnaire based on the CSFB treatment thresholds set out in AHDB Cereals & Oilseeds Information Sheet 43. 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) and again when at the three–four leaf growth stages (Assessment 2). A total of 62,000 ha of oilseed rape was assessed in this survey, which equates to about 11% of the total UK winter oilseed rape area. Only crops which had not been seed-treated with neonicotinoids were assessed. No statistics were calculated, instead this report presents the straight survey results. CSFB damage was present on 65% of crops at Assessment 1 and 69% of crops at Assessment 2. However, at Assessment 1, just 8% of crops had levels of damage in excess of 50% leaf area lost, whilst by Assessment 2 this had reduced to 4%.

CSFB damage was more widely dispersed around the country than in 2014, with the highest levels of damage (crops with severe damage – leaf loss in excess of 75%) reported in Leicestershire, Northamptonshire, Essex, Bedfordshire, Cambridgeshire, and Yorkshire at Assessment 1 and with a hotspot of severe damage also appearing in Buckinghamshire at Assessment 2.

In the most severe cases of damage, there were a number of crop losses recorded. At Assessment 1 there were 0.8% of the crops in the assessment area lost, equivalent to 5,000 ha of the total oilseed rape area, and at Assessment 2 the level of losses rose to 1.0%, equivalent to 6,000 ha of the total winter oilseed rape area. The main areas of crop losses reported in the survey (in order of greatest losses first) were Buckinghamshire, Cambridgeshire, Essex, East Yorkshire, Suffolk, Lincolnshire, Northamptonshire, North Yorkshire, Hampshire and Bedfordshire. There were still a number of crops present at the time of assessment 2 where a decision had yet to be made as to whether they remained viable or not.

CSFB was not the only cause of crop losses this season, with an additional 1.9% of the area, equivalent to 11,000 ha at the national level, reported as lost at Assessment 1 rising to 3.1% reported as lost at Assessment 2, equivalent to 18,000 ha at the national level, due to other reasons, predominantly slug grazing.