So it was doubly sad to read that other imported tree pests are rampant in the UK. Here's an extract from The Guardian's article....
A young horse chestnut tree in a west London garden was bleeding a rust-coloured liquid down its bark last week. As it dried, it left a black, tar-like stain several feet long. Two streets away, another horse chestnut had prematurely shed its leaves in July. A fungal pathogen known as bleeding canker was killing the first tree from the inside, while the horse chestnut leaf miner moth was destroying the second. Neither tree will survive the winter.
Meanwhile, in Plymouth last week, parts of a mature cypress hedge were turning a lighter olive-grey than similar trees around it. It was a sure but ominous sign that a fungus-like pathogen known as Phytophthora lateralis was attacking its roots and working its way up the inner bark. The disease has left a swath of destruction in the western states of the US and Canada, but its arrival in England for the first time has struck fear in gardeners' hearts.
In scenes reminiscent of foot and mouth disease 10 years ago, the trees were quickly felled, and their roots burnt because the infection can spread through soil.
Plant pathogens are on the rise globally and Britain is susceptible because of our increasingly warm, wet winters and the globalisation of trade, which has enabled us to fuel our love of gardens by importing millions of exotic plants, many of which can arrive diseased.
SPECIES AT RISKHORSE CHESTNUT At risk from both the 'alien' leaf miner moth, which causes them to shed their leaves early, and the fatal bleeding canker disease.
CYPRESS/YEW The deadly Phytophthora lateralis pathogen attacks both the trunk and roots, withering the evergreen host's leaves and resulting in death.
OAK Acute oak decline causes the tree to suffer stem bleeding from cracks in the bark. Has resulted in the deaths of oaks throughout the Midlands and south.
LARCH A fungus-like pathogen, Phytophthora ramorum, causes extensive damage. Recently found on larch and conifer species across the north-west and Scotland.
PLANE Recent cases in north London confirm the arrival of deadly fungus, Ceratocystis platani, which attacks and weakens plane tree trunks and branches.
So take care if you're tempted to import from another country. I don't know if buying from a reputable source can prevent the spread, as stock may be sold unknowing that disease is present until it's too late.