Gardeners are plagued by so many pests and diseases that the last thing we want is to bring more into Scotland after a holiday in mainland Europe. 
We all know how Dutch Elm Disease dramatically changed the landscape last century: I remember the sadness of felling a fine old tree in my own garden. 
And Ash Dieback’s recent devastation has been just as bad. I’ve witnessed it on my own ground as the disease rampaged through my well-established and sapling ash trees. 
Equally bad fungal disorders can also affect other garden plants. Phytophora ramorum, first found on a viburnum in a Sussex garden centre, can infect many species including camellias, magnolias, witch hazels and blaeberry. Like Ash Dieback it was an accidental import.
International trade has often been responsible. Rather than being finished off by week or month-long journeys across the world, pests and disorders arrive fit and well, courtesy of much speedier container ships.
Pests and diseases can hitchhike in timber products as well as in living trees now that timber is moved quickly around the world in these containers. 
One of the most famous arrivals to our shores was the scourge of earthworms, the New Zealand flatworm. Unlike in its native New Zealand, the worm has no natural predators in Scotland so will clear the garden of earthworms.
Other dreadful pests include the destructive lily beetle, pictured, which arrived in plants a little over a century ago and recently reached Scotland. 
In the last few years the rosemary beetle has arrived. It attacks sage, lavender and other herbs as well as rosemary.
Although a few fungal disorders and strong flying pests can be blown in, humans are and have been responsible for unintentionally importing many of our garden headaches. 
Victorian plant hunters ruthlessly plundered the world’s flora to bring back prize specimens including the infamous Japanese knotweed.
It’s vitally important that we behave responsibly and aren’t tempted to bring home trophies from mainland Europe or even from the south of England. This could help spread pests and diseases which may not yet be obvious.
With our changing climate, pests and diseases that used to be killed off by prolonged hard frosts and snow cover can now become established because of milder winters. And the global trade in plants and plant products increases the opportunities for introductions.
If we buy locally grown plants we can be more confident that our purchase will be safe for our area. But plants from friends or relatives who live further afield could pose problems, however healthy the plant looks and however well meaning the donor.
So vigilance is vital. Try to identify any unfamiliar insects: iSpot and other portals are useful for this. If a plant is suffering from an unfamiliar disease, try to find out what it is. 
A local garden centre may be able to identify the pathogen and when taking a sample for identification, put a freshly cut sample in a clear, sealed plastic bag to keep it as fresh as possible and prevent it from escaping.
The Scottish Government has a Plant Pest and Disease Guide available online and the Plant Health Centre Scotland has news of diseases and pests.


Plant of the week

Oriental Hybrid Lily ‘virtuoso’ bears large trumpet shaped, highly scented flowers in a delicate mix of pale pink and white with a scattering of purple spots. Most suitable for growing in large pots as oriental lilies are not fully hardy; take them in to a cold greenhouse or bright shed over winter. ‘Virtuoso’ will need staking as it grows to 90-100cm. 
Oriental lilies prefer acid soils so use ericaceous compost. You will need deep pots as lily bulbs must be planted at a depth of at least twice the height of the bulb. Mix grit through the compost and add a little extra to the surface of the compost on which you will place the bulb; lilies hate to be soggy. 
All parts of lilies, including the pollen, are toxic to cats.