Disturbance of the knotweed by humans and wildlife is frequent; there are several wildlife "runs" as well as fox earths and rabbit warrens both within and adjacent to the site. The knotweed's sole overland means of reproduction is via mechanical means(ie, "interference" by humans, machinery and animals). The brittle knotweed material relishes such disturbance.
Note the fragment of fresh growth here has not wilted: contact with water or soil will produce a complete and new plant within 10 days at this time of year.