Zero management often best approach to invasive knotweed
Japanese, Sakhaline and Bohemian knotweed are non-native invasive plant species that can cause significant ecological and economic damage. Reducing or eliminating them is very difficult. INBO too is helping to find solutions.
For three years, we investigated the surface change in 45 populations under low-frequency mowing or zero management. Our research shows statistically that under zero management, surface expansion is on average as fast as under low-frequency mowing management. However, mowing management results vary more than zero management.We observed both shrinkage and increase in surface area. The outcome of mowing management is very difficult to predict. The observed variation is probably caused by shading, competition with other plants or nutrient richness of the soil at a growth site.
We also examined manual uprooting. Knotweed can be effectively and efficiently controlled with this provided the rhizomes are not much deeper than about half a metre. We recommend the use of manual uprooting particularly for the control of recent populations because these have not yet developed an extensive rhizome network.
For invasive knotweed, proactive and careful work is necessary. For established patches, we recommend maintaining zero management where possible. If mowing management is desirable, be extra careful to avoid spreading fragments.