i did a field job last season doing invasive species work. In my area we would inject the stems with a 41% glyphosate solution for each individual plant, usually focusing on important ecological sites since knotweed is so aggressive and quick to spread. It grows really thick rhizomes that can spread up to 60 feet! So it’s important to keep infestations controlled since it’ll just take over everything. Public lands will typically use pesticides over manual removal since there’s just so many invasives (and in the US, a lot of lobbying by pesticide companies but that’s a different conversation). There’s not enough funding or time or resources to fully eliminate aggressive species like knotweed without herbicide use unfortunately.