Manual removal of Reynoutria japonica along a river in Canada
Reynoutria japonica (Polygonaceae: EPPO List of Invasive Alien Plants) is native to Japan and is a widespread invasive alien plant in the EPPO region. The species can have negative impacts on areas where it invades, reducing biological diversity and having negative impacts on ecosystem services. The species can degrade urban areas and damage infrastructure causing significant economic impact. R. japonica is also invasive in other regions of the world, and in Canada a study on management measures was conducted in the province of Québec along the Etchemin River. The study assessed the effectiveness of controlling plant populations by manually removing rhizomes which have recently rooted after being deposited by floodwaters. This method was conducted in two areas of the river where the first area was heavily invaded by R. japonica, and the second area was only sparsely invaded. In the heavily invaded area, 1 550 and 737 R. japonica rhizome fragments were found and removed in 2019 and 2020, respectively. Only 21 fragments were found and removed in the sparsely invaded area in 2020. Along sparsely invaded riverbanks, a rapid removal campaign for R. japonica cost an estimated 142 CAD (96 EUR) per rhizome fragment removed. In highly invaded river stretches which can generate thousands of fragments annually, removing these fragments yearly is likely to incur significant costs and effort and is unsustainable. However, in the sparsely invaded areas, manual removal campaigns may be used to reduce the number of propagules.
Sources
Rouleau G, Bouchard M, Matte R, Lavoie C (2023) Effectiveness and cost of a rapid response campaign against Japanese knotweed (Reynoutria japonica) along a Canadian river. Invasive Plant Science Management 16(2),124-129. https://doi.org/10.1017/inp.2023.11