Knotweed

What would you do about this knotweed? I tilled 10″ deep and seeded grass in the spring. It struggled and died with the heat waves. Should I pull it and risk turning up more seeds or cut it at the base to let the roots rot out. Does anyone know if knotweed will come back from roots only? I’m hoping to try again one more time next year with some hardier fescue grass. Thanks very much!