The Food & Environment Research Agency (FERA) has discovered outbreaks in Northamptonshire and Cheshire and more than 15,000 infected poinsettia were recently returned to the Netherlands.
Certis account manager Martin Donnelly said: "They are the bane of many poinsettia growers' lives and these outbreaks are showing unusually early tobacco whitefly activity - posing even more of a concern."
According to FERA plant health policy's Richard McIntosh, there have been problems with herbs imported from Israel and a large consignment of Dipladenia plants from Spain was recently destroyed. But he said the unusually early findings were not necessarily a sign of a worsening problem.
"There are certainly issues because the trade seems to be starting earlier than usual, so there may be a belief or an appearance that problems are worse," said McIntosh. "Also, our inspectors are keeping a close eye because it is a priority for them to pick it up as early as possible."
FERA is currently undertaking an evaluation of the UK's protected zone status for Bemisia tabaci and McIntosh said this would be completed soon. ADAS consultant Andrew Hewson agreed, adding that pest activity had been early given the cold winter.
He explained: "The pests seem to have adapted, but maybe the fact that we have more nurseries under protection is a factor." He added that late frosts are the biggest problem for growers keen to get material into garden centres.
"While the damage is largely superficial and the plants will recover over the summer, it has hit soft, spring growth at a crucial time and rendered some stock unsaleable for now, which exacerbates the problem of stock shortages this spring," Hewson warned.
"The other point is winter root damage and the full effects of this are sometimes not seen until early summer, which means some stock despatched to garden centres in the spring and in good faith by nurseries has to be taken off sale."
Bemisia tabaci is a notifiable pest. If its presence is suspected, FERA inspectors must be informed immediately.