Can Land Managers Control Japanese Knotweed? Lessons from Control Tests in Belgium

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 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.