A recent survey carried out by ADAMA has shown that two-thirds of OSR growers in the UK aren’t happy with the level of insect control being achieved on farm – highlighting the importance of safeguarding the natural predatory effect of beneficial organisms. Charlotte Cunningham reports.

Results from the survey indicated that 66% of OSR growers are dissatisfied with the level of protection delivered by their current insecticide programmes, with 46% also claiming they are unable to maintain an acceptable level of control with the range of products available.

Growers are therefore advised to adopt an integrated approach to insect control, with the protection of beneficial organisms a key tactic according to Melanie Wardle, insecticide product manager for ADAMA.

“As winter OSR crops begin to flower and warmer spring weather approaches, growers and agronomists should be on the lookout for cabbage seed weevil activity,” Melanie explains, “Especially as our survey highlighted that growers perceive these insects to be one of the dominant threats at this time of year.”

Seed weevils have the potential to cause significant yield losses in OSR, not only as a result of the direct damage caused by laying their eggs in developing pods, but also by subsequent populations of brassica pod midges which use the holes left by the hatched weevil larvae to access rapeseed pods and lay their own eggs, she adds.

Known hotspots

“Growers in known hotspots such as Yorkshire and Lincolnshire must be particularly vigilant and should safeguard the natural predatory effect of beneficial organisms in order to optimise control.

“One way of achieving this, when insect populations have reached threshold, is to use a pesticide which has a lower residual impact on advantageous predators – a strategy which 54% of survey respondents are already adopting.

“If a pyrethroid-based insecticide is deemed the most appropriate mode of action, care should be taken to select one which has a reduced impact on populations of useful organisms. Mavrik (240 g/litre tau-fluvalinate) will provide fast acting contact control of cabbage seed weevils and has been proven to have a lower residual impact on beneficial insects compared to other pyrethroids. Switching to tau-fluvalinate can therefore maximise the valuable predatory role of these organisms as part of an integrated pest management programme.”

The survey also showed that more than a quarter (27.5%) of the 171 farmers and agronomists questioned are actively monitoring for populations of beneficial organisms in OSR and that 88% of growers are encouraging populations of beneficials by using field margins to provide a favourable habitat (53%) and modifying their spray timings to avoid critical times in their lifecycle (68%).