There are a ton of really horrible invasive weeds out there, but Japanese knotweed might be the horriblest. In the UK it has gotten so bad that you have trouble getting a mortgage if the plant is found within seven meters of your property line, partly because its roots can damage building foundations.
The plant is bad in the US but we haven’t taken it quite that seriously, although places in New Hampshire are ramping up their efforts. A UNH researcher, for example, calls it “hazardous waste” because of how it can smother all the plants around it. It also spreads very easily; just an inch or so of material lying on the ground will root and create a new plant – in fact, one of the reasons it is common along roads is that towns mow roadsides, which chops up the plants and spreads bits further down the way.
In my town we have just mapped all the roadside Japanese knotweed we can find, in hopes that town meeting will pay to start eradicating it – mostly by spraying Roundup, which is the only really effective way to kill the damn stuff. We found 25 spots where it grew, most pretty small but a couple patches that are dozens of feet long.
Maybe we could hire some goats! There’s a story in Foster’s about goats eating knotweed. My experience, however, is that this will be, at best, a holding pattern; they’ll never eat so much that the plant won’t grow back, year after year.
Biocontrols, as a general rule, never eradicate the problem, only contain it. If you want to wipe out something you really need chemicals.