Control methods based on interspecific competition, mulching and regular mechanical maintenance against Japanese knotweed: Feedback on six years of monitoring

Abstract

Japanese knotweed (Fallopia japonica) is very present on the banks of the Rhône, colonizing more and more areas on the banks of the river. Since 2015, the Compagnie Nationale du Rhône (CNR) has been conducting experiments to control Japanese knotweed on 15 plots located on the restored Cornas lone in order to measure the effect of three management practices: mulching, repeated mechanical actions and the planting of competitive or native species (Viburnum opulus and Salix purpurea) and/or have an allelopathic power (Ailanthus altissima, Rhamnus frangula, Sambucus ebulus, Juglans regia). Each year between March and September, knotweed stems are counted, measured, located, and photographed every month on each plot. After six years, the results showed that the density of knotweed stems has decreased by 65 to 100% on all plots. Indeed, the monthly mowing and mulching by felt exhaust the rhizomes for three years giving time to competitive species to generate more and more intense shade on the plots. At the same time, native and spontaneous vegetation began to return to the lone. Subsequently, the cessation of monthly mechanical mowing in 2022 will confirm the long-term sustainable methods.