Japanese knotweed Fallopia japonica is an extremely abundant invasive plant in Belgium and surrounding countries. To date, no eradication method is available for land managers facing the invasion of this rhizomatous plant. We tested different chemical herbicides with two application methods (spraying and stem injection), as well as mechanical treatments, on knotweed clones throughout southern Belgium. The tested control methods were selected to be potentially usable by managers, e.g., using legally accepted rates for herbicides. Stem volume, height and density reduction were assessed after one or two years, depending on the control method. Labor estimations were made for each control method. No tested control method completely eradicated the clones. Stem injection with glyphosate-based herbicide (3.6 kg.ha -1 of acid equivalent (AE) glyphosate) caused the most damage, i.e., no sprouting shoots were observed the year following the injection. The following year, though, stunted shoots appeared. Among the mechanical control methods, repeated cuts combined with native tree transplanting most appreciably reduced knotweed development.The most efficient methods we tested could curb knotweed invasion, but are not likely to be effective in eradicating the species. As such, they should be included in a more integrated restoration strategy, together with prevention and public awareness campaigns.

La crassule des étangs (Crassula helmsii) est une plante invasive (ou exotique envahissante) qui représente un risque environnemental pour les milieux aquatiques en Belgique et, plus globalement, en Europe. Pour contrôler cette espèce, les acteurs de terrain disposent d’une littérature a priori abondante, ainsi que de plusieurs bases de données relatives à sa distribution spatiale. Néanmoins, les gestionnaires peuvent vite se sentir désarmés, d’une part par le manque de clarté sur les moyens à mettre en œuvre afin d’endiguer la propagation de l’espèce et, d’autre part, par le manque d’exhaustivité des bases de données. S’ajoute à cela une insuffisance de littérature sur les vecteurs de dissémination à travers les paysages.