Following recent outbreaks of Bemisia Tabaci or tobacco whitefly, horticultural crop protection specialists Certis are advising a preventative strategy to guard against the risk posed to ornamental crops.
Outbreaks have been discovered in Northamptonshire and Cheshire by The Food and Environment Research Agency’s (FERA) Plant Clinic and unless controlled, can result in destruction of the crop.
"Poinsettias are often the major source of tobacco whitefly outbreaks in the UK," explains Certis’ Martin Donnelly but he points out that with a wide host range, including vegetables and salads, as well as ornamental crops, their introduction can occur from a range of imported plants and cuttings.
"Not only do the pests cause direct feeding damage to the crop but the tobacco whitefly also act as a vector to over 110 virus species – including cucurbit yellow stunting disorder virus and tomato yellow leaf curl virus.
"Indirect damage can also be caused by the development of sooty moulds on honeydew excreted by the whitefly on the host plant," adds Martin.
"They are the bane of many poinsettia growers, and these recent outbreaks are showing unusually early tobacco whitefly activity – posing even more of a concern," he warns.
Martin advises growers ensure all new plant material is thoroughly inspected as it arrives at the nursery. "Consider introducing quarantine areas, keeping the recently imported stocks in isolation for close monitoring, to prevent the spread of any potential infestation," he says.
For growers inspecting crops, Martin explains that compared to other whitefly species, the tobacco whitefly adults will appear slightly smaller and will tend to hold their wings slightly apart at an angle to the body when resting – exposing a yellow body.
An integrated and programmed approach to prevention is advised. On protected containerised ornamentals Martin recommends applying Gazelle SG (acetamiprid) or Oberon (spiromesifen) as initial clean up treatments as soon as the plants are brought into the nursery.
"And then around two weeks after the initial clean up, the release of biological control agents can begin with the introduction of an Eretmocerus eremicus and Encarsia mix, at an advised high rate.
"As a parasitic wasp, Encarsia has activity against tobacco whitefly – as well as being widely established in glasshouse whitefly control strategies," he explains.
"Eretmocerus eremicus, another parasitic wasp, fits very well in conjunction with Encarsia. Particularly useful in high temperatures when the establishment of Encarsia can be affected," advises Martin. "Eretmocerus are strong against tobacco whitefly so form an important component within a robust strategy," he adds.
Growers should keep up with the regular release of biologicals at weekly or fortnightly intervals for the next five or six weeks. Then a reduced rate of Encarsia can be used if no whitefly are present within the crop and as temperatures start to fall.
As a further measure, the strategy can be supplemented with the use of yellow sticky traps to monitor whitefly presence.
A further application of Oberon can also be used alongside the biological programme, explains Martin. "Offering effective, long lasting control that’s compatible within an integrated control programme – even once biologicals have become established," he advises.
As a notifiable pest, if their presence is suspected, the FERA plant health and seed inspectors (PHSI) should be informed immediately.
