Plant sampling conducted by ADAS for HGCA has provided an insight into cabbage stem flea beetle (CSFB) larvae levels in oilseed rape crops.
Eight out of 14 oilseed rape crop sites sampled for cabbage stem lea beetle larvae in February this year were above published spray thresholds. The survey was commissioned by HGCA to investigate CSFB larval populations in seven of the worst-affected counties identified in HGCA’s autumn 2014 snapshot assessment of CSFB losses in the crop.
In Bedfordshire, Cambridgeshire, Hampshire, Hertfordshire, Northamptonshire, Suffolk and Surrey, 25 random plants were taken from two sites during February 17–26, 2015 – one site of which had a ‘high’ and one of which had a ‘low’ adult CSFB pressure.
In total 14 sites were sampled and petioles and stems were dissected at ADAS laboratories to determine average larvae numbers at each site.
The sampling revealed variation in larval counts across counties. Eight of the sites were above the published spray treatment threshold of five larvae per plant – five of these were high-pressure sites.
All sites were found to contain less than an average of 10 larvae per plant, with the exception of the high-pressure site in Cambridgeshire.
At this site, larvae averaged 28 per plant, with one plant containing 59 larvae (57 of which were located in the leaf petioles).
These findings follow the publication of the ‘spring assessment’ results by the Food and Environment Research Agency (Fera).
AHDB research manager Caroline Nicholls says: “The Fera spring assessment results were based on 25 plants taken across 50 sites and found a national average of 1.4 larvae per plant.
"The average in our study was 6.6 larvae per plant but, as we focused on the worst affected counties, this higher figure is not surprising.
“These are interim project results and the WOSR located at the sites will be taken to yield to help improve our understanding of the relationship between CSFB pressures and yield impacts.”
The ADAS-led cabbage stem flea beetle larval survey started in January 2015 and will finish in October 2015.