A dry summer, followed by a warm September, will give OSR growers a clearer indication of potential risks from cabbage stem flea beetle this autumn. But open autumn conditions and milder temperatures through winter will influence larvae numbers, and potential impacts on yields.
The dynamics of the cabbage stem flea beetle (CSFB) populations are certainly changing with climatic conditions, with hugely increased pest pressure impacting on yields over recent seasons, reports ADAS research entomologist, Dr Sacha White.
Historically studies had shown little difference in larvae numbers in plants between late autumn and spring. More recently, however, larvae populations have continued to increase through the new year, to be significantly higher in the spring; in some trials last year larvae numbers more than doubled between autumn and spring assessments, for example.
Speaking at a recent iOSR growers meeting, Dr White said: “Despite a perfect storm of conditions which led to very high populations over the past season, however, it does not necessarily follow it will be another epidemic year.”
As with most insect populations, the numbers will be primarily dictated by prevailing weather conditions, which can give growers vital early warning to tailor their decisions.
Dr White said growers would need to adopt a whole range of tools and novel management techniques, which he believes can make CSFB a manageable pest.
This season, Norfolk iOSR grower Chris Eglington is evaluating the potential of a brassica-based green headland, established in an adjacent field before the oilseed rape crop, might serve to trap and hold CSFB away from the intended crop.
In what is believed to be the UK’s first sowing of a crop using a drone, he established the Operation Pollinator seed mix, including fodder radish, direct into a standing pea crop. The aim is to ensure sufficient moisture and microclimate under the peas for the brassica to establish before the OSR.
The intention is that CSFB will be attracted to the mix for their summer diapause period, and will then stay to lay their eggs around the brassicas. The green headland will be left in place until a wheat crop will be drilled through it in late September – which will destroy any CSFB larvae in the mix.
Furthermore, Mr Eglington aims to leave OSR stubbles and encourage volunteers to chit, to attract CSFB away from his sown crop, where the rotation permits.
Leaving green OSR stubbles has shown to be effective in reducing larvae numbers in the new crop in the majority of ADAS-monitored studies, reported Dr White. Trials have shown up to 74% less damage and 67% less larvae in crops where a substantial area of volunteers have been left nearby.
Initial indications are that results are greatest with later established OSR, where the volunteers possibly have longer to establish and act as a reservoir to dilute pest pressure on the establishing crop, he says.
James Fountain, who farms near Whittlesey, Cambridgeshire, said while OSR looked good with plenty of pods at harvest, the effects of CSFB damage did have an impact on crop evenness and maturity.
This season, he has switched from conventional to a hybrid variety, in an initiative to get the crop up and growing away from CSFB and pest damage more consistently, and particularly for spring vigour. For the first time, he is trying a block with cyantraniliprole insecticide seed treatment this autumn.
He is also looking to evaluate different drilling dates, with one block going in after hybrid barley there is a chance for some of the OSR to be established earlier, conditions permitting. OSR going in later, after wheat, will also have been preceded by potatoes, which has previously benefited from the residual fertility, he added.
Dr White said spring vigour of hybrid varieties, along with spring nutrition timing, could have an impact on the plant’s ability to grow away from CSFB damage, along with where larvae are moving in the plant; larvae may be picking up a spring growth response in the plant to trigger a movement into the stems. The use of spring PGRs to adapt crop architecture may also have a role in influencing larvae feeding activity.
Mr Fountain used PGR in the spring for the first time last year, with the aim to shorten tall crops, but also to help create branching and a bigger leaf area for light utilisation.
“Possibly with a hybrid variety sown earlier, hopefully into good conditions, we might have an opportunity to look at managing a crop in the autumn with PGR effects there too,” he added.
Dr White highlighted ADAS monitored trials had shown later sowing, with crops emerging after peak CSFB egg laying, tended to result in fewer larvae in petioles andstems. “Sowing date appears to be hugely influential,” he advised. “There is a huge data set that indicates later sowing will minimise egg laying and resulting larvae numbers.
“But it has to recognise the risks of getting a crop successfully established, along with the workload on farms in the autumn. A range of sowing dates, along with other integrated measures, could effectively help to spread risks.”
THIS season iOSR growers across the country will be undertaking a series of field scale trials to investigate use of spring PGR treatments - to enhance canopy structure and tailor flowering duration – along with Amistar applications to optimise green leaf performance.
The trials will also utilise potential for satellite imagery assessment of field trials, to give real time information that can be integrated into digital ag decision making.
Syngenta iOSR field technical manager, Georgina Wood, said: “New farm technologies enable faster and accurate assessment of crop performance before and after treatments on a field scale.
“With the scale of detail we can begin to pinpoint precisely which crops will benefit from treatments and timings, to give a valuable picture of future potential and advice.”
Crops in the iOSR trials will also be entered into YEN monitoring results, to give a benchmark of physical and financial performance.