Here’s a new review of the literature on using tarps or coverings to block sunlight and control invasive knotweeds (Reynoutria spp.or Fallopia spp.). Dusz et al 2021 (link to abstract and access to free article).

The authors state: “based on the bibliography and survey work, we propose practical recommendations including covering the entire stand, extending the tarping up to 2.5 m beyond its edges for a period of at least six years, and ensuring regular monitoring. Even though tarping does not seem to be a one-size-fits-all solution to eradicate knotweed, it could still be a useful control method once knotweed has become a critical management issue.”