It is suspected the whitefly came into the UK on poinsettia cuttings a few months ago. Bemisia tabaci has entered the country on poinsettias in previous years but this year the problem is worse than normal, according to observations by field officers from crop protection company Certis.
Certis technical officer Alan Horgan said: "It's a lot more problematic than it has been for the past couple of years, and we're not sure why. It could be that propagators overseas are using insecticides routinely rather than approaching (plants) with a more careful management programme."
There are two biotypes of Bemisia tabaci and the strain that attacks poinsettias is more insecticide-resistant. British Protected Ornamentals Association technical committee chairman Michael Smith believes one of the reasons the industry is seeing more outbreaks is that "pesticides are not as effective as they used to be, because the pest is building up immunity".
Smith said more research was needed into what was the most effective insecticide programme against Bemisia. ADAS consultant John Buxton agreed: "Unless money is spent on research into resistance and which bio-controls are effective, it will be a problem again."
Tobacco whitefly is a quarantine pest, so under European law any incidences must be immediately notified to a local Defra plant health and seeds inspector. Outbreaks need to be treated within a prescribed time scale and if any flies remain, the crop must be destroyed.Some growers have suggested it should be removed from the list of notifiable pests as it is becoming more widespread. It is no longer a statutory pest in Holland and most other European countries.
ADAS consultant John Buxton said: "But if it was removed from the list, UK tomato and cucumber growers would be extremely upset as it could decimate their crops."
Unfortunately this news comes as poinsettia growers, such as Roundstone Nurseries, were reporting high demand from retailers and getting excellent media coverage.
Peter Hill of Hill Brothers has been filmed for an item on poinsettias by the BBC programme The One Show, which is due to broadcast on 5 December at 7pm. It was organised by the Flowers & Plants Association.