Management of cabbage stem flea beetle in oilseed rape using short term companion crops

Cabbage stem flea beetle (Pyslliodes chrysocephala) was a relatively minor pest of oilseed rape, causing inconspicuous “shot-holes” in the cotyledons. Plants were protected through the establishment phase by the use on neonicotinoid seed treatments, and crop losses were rare. However, since the removal of these products, CSFB has become a major threat to the oilseed crop in many parts of Europe. In some areas, complete losses have occurred, and in others reduced plant populations and poorly grown plants have occurred.

At NIAB, we have investigated the principle of using companion crops sown with oilseed rape as a means of reducing CSFB damage. Experiments on farm have been carried out in autumn 2015, 2016, and 2017 in the UK. In addition, we have used a crowd sourcing tool to investigate grower practice on farms in the UK and requested information on the level of damage observed in order to identify any grower practices which tended to reduce damage from the pest.

The overall objective of the work was to establish practical management approaches which could easily be adopted on farm to mitigate against the loss of insecticide products, and to maintain oilseed rape productivity.

Using a “companion” species sown with oilseed rape has proved to be an effective means of reducing crop damage. In particular, white mustard appears to attract the beetle preferentially, and allow the oilseed rape to establish successfully (see Table). At one experimental site, white mustard was the only companion which allowed oilseed rape to survive at all (see picture)

Table 1. Table 1. Level of flea beetle damage in oilseed rape established in the east of England with different companion species (1 = no damage, 5 = all plants damaged) Companion Flea beetle damage (1-5) 26th September None 3.7 Fenugreek 2.7 Pak choi 3.3 White mustard 2.0 Buckwheat 3.0

Image 1. Oilseed rape plants surviving under white mustard, autumn 2016. Mustard has been removed in the foreground to show rape plants

The technique is suitable for high risk situations, and the companion should be removed after a few weeks, using either a non-selective herbicide if the oilseed rape variety is herbicide resistant, or a conventional selective herbicide in the autumn. Relying on frost to kill the companions is not recommended for much of northern Europe as temperatures may not be low enough.

Growers should consider constructing their own white mustard and oilseed rape mixture or buying “co-packs” which may be marketed commercially. Small test areas are advised initially so the technique can be explored in different farm situations. Other companion crop species have not proved effective for flea beetle control but may provide other benefits eg. legume companions to provide nitrogen. “Crowd sourcing” data revealed the best approach for reducing pest damage was early drilling, around the first half of August in the UK. Ploughing was generally the optimum cultivation technique, as the better seed beds that this gave allowed for rapid germination and emergence, enabling plants to withstand flea beetle damage.