Be carefully of the sap from knotweeds. The burns are light sensitive. Work with someone who had scars he can't let much sun onto without blisters forming.
For knotweed try stem injection. We had loads at work, the the stems were injected about five years ago. Its only starting yo come back along the drivers edge in the last year. Don't know what was injected suspect roundup?
You can eat Knotweed. Quote ex Google
"Knotweed edible: To begin with, not all parts of the plant are edible (as with rhubarb) and they are only edible at a certain time of the year. The shoots in the spring are tender enough to eat, but they have to be gathered before the stems become hard and woody. The ideal time to eat knotweed is mid-April to May."