Knotweed, while pretty, is one those really ugly invasives. We had, and maybe still have them, around the Soos Creek Hatchery. They lined the stream banks. The roots were so thick and strong that they were an excellent bank protection from flood and erosion. But the crowded out everything and nothing local seems to eat them. Kind like green riprap. They make huge monoculture stands in wet areas driving all other plants, and probably animals, out. Very hard to kill and pieces broken off in flood go downstream and grow there.

I know some NGOs that have spent years of intensive handwork to eliminate knotweed along streams.