It's certainly true that pests and diseases can cross borders in shipped or carried goods, and it makes perfect sense to prevent that.
On the other hand though, it surprises me that there are many issues between Canada and the US, which is essentially one continuous land mass. Pests and diseases really don't know about our "borders" they will cross a political boundary no problem at all and regularly do. This is where I start to wonder, why so much fuss between us.
For the island it's different, there's been a prohibition on shipping out potatoes from here for decades because at some point in history, there was an outbreak of potato scab, and so they wanted to protect the mainland from it. Yet we get imported potatoes in the stores here, with scab on it sometimes and every other kind of disease. Blight included.
Still the prohibition is so old it has just stayed in place.
We have certain pests such as the Spruce budworm that sometimes wreak havoc here, although in fact they can't survive the winter here at all. Every spring they blow across from Nova Scotia.
