Since the withdrawal of neonicotinoid seed treatments in 2013, cabbage stem flea beetle (CSFB), as many farmers know to their cost, can wipe out entire crops, and widespread resistance to pyrethroid insecticides has not helped in controlling the pest.
Although CSFB damage in crops across the country in 2020 and 2021 was less than in previous years, adult CSFB numbers in both seasons were much the same as before in some areas, says ADAS’ Dr Sacha White, who is leading the project looking at reducing the impact of the pest.
“The lower damage levels were probably due to better conditions at establishment and to the industry adopting better pest management, for example adjusting their sowing dates,” says Dr White.
The three-year project, which began in July 2020, has two key areas of work.
The first is to study the pest’s biology and how its life cycle is affected by seasonal variations in climate and habitat.
“It focuses on work that will help improve monitoring the pest, predicting the risk of damage and targeting management strategies,” adds Dr White.
The second area is investigating control methods which can be used on farms.
Several non-chemical control strategies have shown potential, says Dr White.
These include adjusting sowing dates, changing sowing rate, managing stubbles and using trap crops.
“Reliable data on the value of these methods is limited,” he says.
“Our work is exploring a range of controls to identify the effectiveness and reliability of each of them and trying to see where strategies could be combined to improve overall control.”
Getting to grips with the first area involves using traps from Yorkshire to Devon to monitor the migration of adult flea beetles and pinpoint factors driving it.
“The data is being analysed alongside variables such as weather data.
We hope this will allow us to predict the start, size and length of adult migration more accurately.
“We’re monitoring adult feeding damage at sites across the country and comparing this with trapping data to see whether that data can be used to predict damage.”
Laboratory experiments are being conducted to find crop stages which may be preferred by migrating adults.
“This should help optimise the use of volunteer rape as a trap crop by pinpointing the growth stage most attractive to the beetle,” says Dr White.
Assessment of the impact of temperature on egg and larval development in controlled environment experiments is also underway.
“This should allow larval risk to be better predicted and treatments to be better timed.”
Pot experiments are also being used to assess the effect of larvae numbers, the date larvae invade and the condition of the crop at the time of invasion.
This should allow the impact of larvae on crop yield to be determined and mitigation strategies be better deployed.
On-farm, a range of non-pesticide control strategies are being investigated in plot-scale to field-scale trials.
These include sowing date, companion crops, stubble and establishment methods, the use of organic amendments and growth regulators, variety, seed rate and crop nutrition.
To date there have been few surprises, says Dr White.
One particular trial highlighted the importance of sowing date.
“It showed crops emerging during peak beetle migration are at high risk.
That usually peaks in early to mid-September.
Sowing between the third week of August and mid-September risks high damage.
Sowing earlier will likely result in less adult damage.
Sowing later probably reduces larval pressure and possibly leads to lower adult damage as well.”
The trials have also found that companion crops such as buckwheat, berseem clover and fenugreek, using organic amendments such as manure, and leaving stubbles untouched all have potential to reduce CSFB damage.