I understand, Eliza. Yes, Giant Hogweed is a very dangerous and invasive plant. According to the linked article provided by JohnInKansas, the skin sensitivity "leading to terrible blistering burns, followed by skin discoloration and darkening...can persist for years." It's not the sort of plant one wants to spread at all. (Note: My second link failed; sorry.)

As for Japanese Knotweed, we just dig out the roots and mow any remaining shoots; no poison required here in Maine. Young shoots are edible; asparagus-like in taste. We learned from an elderly woman who once lived on our farm that her grandparents planted Japanese Knotweed here to provide shade for their chickens!

Maeve