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Tactics to tackle beetle pressure in OSR crops

Agronomy Issues
Volunteer control in OSR

A dry summer, followed by a warm September, will give oilseed rape growers a clearer indication of potential risks from Cabbage Stem Flea Beetle this autumn.

It will be open autumn conditions, combined with milder temperatures through winter, however, that will ultimately influence larvae numbers, and the potential impacts on yields.

Flea beetle

The dynamics of the CSFB populations are certainly changing with climatic conditions, with hugely increased pest pressure impacting on yields over recent seasons, reported 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 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.  

“Despite a perfect storm of conditions that led to very high populations over the past season, however, it doesn’t necessarily follow that it will be another epidemic year,” he pointed out.

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 Sacha White ADAS

There’s no one silver bullet for control of CSFB, but a range of tactics can make it a manageable pest, believes Dr Sacha White

Sacha advocated growers will need to adopt a whole range of tools and novel management techniques, which he believes can make CSFB a manageable pest.

Pick’n’mix tools to tackle CSFB

  • Leave stubbles and volunteers
  • Later drilling dates
  • Establishment technique
  • Companion cropping
  • Variety vigour
  • Autumn nutrition
  • Spring fertiliser timing
  • PGR canopy management
  • Encourage beneficial predators
  • Winter defoliation

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 had 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.

Crop Angel drone sowing green headland mix in peas

Chris Eglington’s Crop Angel drone business has fitted a sowing unit capable of spinning on seed at 7 kg/ha into the standing crop, which enabled the sowing of green headland into peas in early July

The aim 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, Chris aims to leave OSR stubbles and encourage volunteers to chit, to attract CSFB away from his sown crop, where the rotation permits.

Chris Eglington iOSR grower

Results of his on-farm grazing trials to remove CSFB larvae will give an indication if the technique could be used again, reports Chris Eglington. Post-harvest results to follow….

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 Sacha 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 believed. 

A secondary benefit is that any larvae that infests volunteers are killed off when it is destroyed and further reduces background numbers.

Further farm trials with iOSR growers could look at sequential passes with cultivator and rolls in OSR stubbles, to trigger successive flushes of volunteers and evaluate what size and timing appears most attractive to CSFB, added Sacha. 

Read more on iOSR growers’ autumn actions to tackle CSFB and other crop agronomy decisions

Along with details of iOSR farm trials for the crop’s agronomy next season


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