Are Japanese knotweed (Fallopia japonica) control and eradication interventions effective? CEE Review 05-015

  • Published source details Kabat T.J., Stewart G.B. & Pullin A.S. (2006) Are Japanese knotweed (Fallopia japonica) control and eradication interventions effective? CEE Review 05-015. CEE (Collaboration for Environmental Evidence) Systematic Reviews, SR21.


Japanese knotweed Fallopia japonica is listed as one of the IUCN's top 100 invasive plant species. It is highly competitive, able to regenerate from root and stem fragments, and is very difficult to control. Japanese knotweed control and eradication attempts have used a range of mechanical and chemical techniques. Many agencies publish guidelines detailing the effectiveness of these various methods, but a critical appraisal of empirical evidence regarding effectiveness of different methods has not previously been undertaken.

A systematic review (see: for methodology) was undertaken to evaluate if Japanese knotweed control and eradication interventions are effective. Objectives also included an assessment of whether treatment effectiveness was influenced by: environmental and geographical factors; operational level variables; and hybridisation and species variety.

All six interventions investigated by meta-analysis (glyphosate application alone; imazapyr application alone; glyphosate and imazapyr in combination; cutting alone; cutting followed by injecting the hollow stem with glyphosate; or cutting followed by spraying regrowth with glyphosate) produced statistically significant decreases in knotweed abundance in the short-term, except for cutting alone. However, the ecological significance of their impacts is uncertain, and there is no robust evidence available regarding long-term effectiveness. Uncertainty is exacerbated by the small number of individual effect sizes, the limitations of the pooled studies and the high heterogeneity among included studies. Existing available evidence is insufficient to derive generic evidence-based management guidance for using these techniques. These conclusions are supported by analysis of lower quality data. Variation in effectiveness was evident both within and between treatments, but this could not be linked to any ecological or intervention-related variables.

No conclusive evidence was found for differences in effectiveness of management techniques due to taxonomic variation. Available evidence suggests that the six techniques analysed will not eradicate Japanese or hybrid knotweed in the short-term.

The review highlights a lack of readily-available, long-term, robust, controlled experiments assessing the effects of the full range of management techniques used against Japanese and hybrid knotweed. The authors of this review are aware of control methods in use other than the six methods analysed. However, as some results are not made readily available, the effectiveness of some control and eradication methods cannot be tested. Readers must therefore put the evidence presented here into a broader context of poor data accessibility. This review recommends further research into methods used to control and eradicate Japanese knotweed.

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