I just found out about Japanese Knotweed about a month ago because some has been spotted in Prince Rupert. From what I've read, you can't even get house insurance in England if you have some on your property because of the amount of damage this tenacious plant does to buildings and any other infrastructure. Apparently it will propagate from the tiniest fragment of plant material and grows quickly. If what I've read is correct, herbicides have to be injected into the plant at repeated intervals in order to fully kill it.
Giant Hogweed has made it's way into quite a few areas in BC - scary stuff! When I was growing up, we had common hogweed (cow parsnip) by our back creek, which is fairly innocuous (and, in fact, edible). If it weren't for bcinvasives.ca, I wouldn't have known how dangerous the Giant Hogweed is. I definitely watch for it when hiking around in the Northwest.