There is something called a "phyto-sanitary certificate". The seller has to fill it out and (I guess) get it approved by their government, which must involve some kind of inspections - or maybe just paperwork and paying a fee.
When imported into the USA (or other countries that use the same system), if Customs stops the box and examines it, if there is anything organic and alive, like seeds or plants, there has to also be a "phyto-sanitary certificate" or they'll destroy it (or take it home for their own garden).
The other way to import plants or seeds is to just mail them, and hope Customs doesn't notice. Then it is your responsibility not to import diseases and pests that can cause billions of dollars worth of agricultural damage.
As climate change keeps increasing, the pests that thrive in any given area change. So your region may have been free of the ZYZ disease or insect because it used to be too cold or too dry or too wet in certain seasons.
Now that you've changed a half-zone or so of winter hardiness, and rainfall patterns change, and spring-summer-fall and daily temperature patterns also change, the only reason some of those pests are still absent from your area is that they have not yet been re-introduced.
Every time we import plants or soil more than 50-100 miles, we may discover that TODAY, our region IS a happy home for some pest that has not thrived there for thousands of years.
But my theory is that attempts to quarantine entire regions and continents are doomed. Some biologist or ecologist, decades or hundreds of years ago, proposed an approximation: "Everything is everywhere." With living things, especially bacteria and fungi that can form spores, or anything airborne, or anything that cling to the shoe soles of an air traveler, all it takes is one spore in a favorable spot, and there will be thousands, then millions, then trillions, faster than you can say "I never saw one of THOSE around here before!"
His theory was that what counts is whether the conditions are favorable to that microbe or plant. If the conditions are favorable, that species will find and colonize that spot. Eventually, or sooner.
No matter how carefully we clean our spades and wash bare-root transplants.
And whether INTENTIONAL cross-border imports are accompanied by paperwork, or not.
