He said the cold-hardy New Zealand mealybug kills meconopsis and primula roots and could have come in on a tree fern log. Cox added that Australia and New Zealand have "stringent regulations on imports, so why do we import plants from New Zealand?
"I can't understand if we understand if we know all these pests and diseases are in Australia and New Zealand, why don't we apply the same rules to importation, for bare root at the very least, or better still not import from Australia and New Zealand. The mealybug could kill all the meconopsis in Scotland."
He said there had been an outbreak in the last six months in Scotland, which could eat the roots of cordyline, dendrobium, dianthus, erica, eucryphia, gentiana, ozothamus, rhododendron and rhopalostylis, among others. Grasses, tomatoes and heather can also be affected.
Defra's UK Plant Risk Register states: "Polyphagous root-feeding mealybug endemic in New Zealand and now present in Scotland and northern England. Though most hosts suffer minor impacts, large populations can build up on some hosts such as Meconopsis and cause damage. Stakeholder groups may wish to continue monitoring developments, including any spread to the wider environment, i.e. heather."
Symptoms are underperforming plants with 2-3 mm insects covered in a golden yellow wax attached to the roots.
The non-native golden root mealybug, Chryseococcus arecae was first recorded outside Australasia in the UK in Dunblane, Perthshire in September 2012, than at a garden in Ross-shire in 2013. The mealybug is a native of New Zealand that unlike other root mealybug species found in Britain can be found on the roots of outdoor plants all year round.
The RHS said there are no pesticide controls for root mealybugs in open ground and infested plants should be burnt.