I’m not familiar with Tumbleweed so I can’t comment on that. Roundup and the stronger version we sell called Kleenup both can knock knotweed back but it usually takes and ongoing assault to get knotweed under control…rarely is a single application enough. Brace yourself for a long battle. Here’s a link you might find helpful: https://www.thespruce.com/eradication-of-japanese-knotweed-plants-2131201