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Summary

A systematic review of the effectiveness of

Japanese knotweed (Fallopia japonica) control and eradication methods

A systematic review of the effectiveness of

Japanese knotweed (Fallopia japonica) control and eradication methods

Background

Tamara J. Kabat, Andrew S. Pullin and Gavin B. Stewart Centre for Evidence-Based Conservation, School of Biosciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, United Kingdom

Tamara J. Kabat, Andrew S. Pullin and Gavin B. Stewart Centre for Evidence-Based Conservation, School of Biosciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, United Kingdom

Systematic review methodology was used to critically appraise evidence for the

effectiveness of Japanese knotweed control and eradication methods. Meta-analyses were

used to examine the use of glyphosate herbicide and cutting as management techniques.

Neither technique is shown to be effective in the short-term, therefore long-term

management programmes should be established. Further robust research needs to be

conducted to test these and other methods of control and eradication under different

circumstances, and in combination with each other.

Methodology

Systematic review methodology uses a comprehensive literature search to compile and assess a wide range of published and unpublished literature. Studies are included into the review using a series of specific selection

criteria. Where possible, meta-analysis is used to combine results from different studies to increase statistical power and determine the overall effect of the interventions being investigated.

Very few studies presented data suitable for meta-analysis, therefore only glyphosate herbicide and cutting techniques used alone were investigated

(Figures 1 and 2). Cohen’s D effect sizes were derived from the treatment and control mean abundance data, standard deviations and sample sizes extracted from the primary studies. Data were compared across studies using DerSimonian and Laird random effects standardised mean difference meta-analysis.

Implications for conservation practice

The preliminary results indicate that eradication of Japanese knotweed

infestations will not occur within a short timeframe when using glyphosate or cutting treatments alone. There is anecdotal evidence that long-term control using these two methods will eradicate knotweed, therefore a long-term control programme should be established when using cutting or glyphosate.

While high-quality research is lacking, anecdotal evidence indicates that different treatment methods, when used together, may increase effectiveness of Japanese knotweed control. This includes using mechanical and chemical techniques together (i.e. cutting and

glyphosate), or multiple applications of treatments.

Japanese knotweed has become a serious weed threat across the world, and has been described as one of the IUCN’s top 100 invasive species. It is a vigorous plant that regenerates readily, and is difficult to control using mechanical and chemical techniques. Eradication typically takes several years to achieve, but there is a desire to

increase the effectiveness of different techniques to attempt to reduce this timeframe. A critical appraisal of the effectiveness of different control and eradication methods has not been previously undertaken. United Utilities PLC identified the need to evaluate control and eradication

methods used for Japanese knotweed under a variety of circumstances and time periods.

AcknowledgementsWe would like to thank all stakeholder organisations and individuals for their support and valuable contributions throughout the systematic review process, but most notably: Lois Child (University of Loughborough, UK), Trevor Renals (Environment Agency, UK), Timothy

Miller (Washington State University, USA), Alison Halpern (Washington State Noxious Weed Control Board, USA), and Simon Ford (The National Trust, UK). We are also grateful to colleagues at the CEBC for their assistance during the review. Support for this review was

provided by United Utilities PLC, English Nature, and the UK Natural Environment Research Council.

Implications for further research

This review highlights a lack of readily-available, long-term, robust, controlled experiments assessing the effects of

management techniques used against Japanese knotweed. Further research should focus on long-term experiments on the effectiveness of both the many herbicides available and the various mechanical techniques. Experiments should focus on creating more effective combinations of these

techniques to manage knotweed, and also on techniques that can be used in different situations, such as sensitive and non-sensitive areas.

This review also highlights the importance of making data from monitoring of control & eradication programmes more

readily available so that it can be effectively evaluated. This includes unpublished organisational reports, conference proceedings and web-based materials (e.g. on www.ConservationEvidence.com), as well as peer-reviewed publications.

Figure 1. Forrest plot results for glyphosate herbicide only. Only four studies presented suitable data for analysis. Glyphosate did not significantly decrease knotweed abundance within 11 to 30 months (P = 0.094).

Figure 2. Forrest plot results for cutting interventions only. Only four studies

presented suitable data for analysis. Cutting did not significantly decrease knotweed abundance within 5 to 17 months (P = 0.764). Only one of these experiments showed a significantly reduced knotweed abundance; however, this was a very short-term experiment (approx. 5 months) looking at planted rhizomes and is not representative of naturally-growing infestations.

Standardised Mean diff.-12.8616 0 12.8616

Study % Weight

Standardised Mean diff.

(95% CI)

-6.34 (-12.86,0.17) Figueroa- unpaved 8.1

-5.83 (-11.87,0.21) Figueroa-paved 9.2

-1.46 (-3.36,0.43) Child et al. 36.6

-0.29 (-1.43,0.85) Scott & Marrs 46.1

-1.72 (-3.74,0.29) Overall (95% CI)

Standardised Mean diff.-3.29086 0 3.29086

Study % Weight

Standardised Mean diff.

(95% CI)

-1.58 (-2.04,-1.12) Seiger & Merchant 29.5

1.66 (0.02,3.29) Beerling & Palmer 21.2

-0.53 (-1.80,0.73) Bimova et al. japonica 24.1

0.14 (-0.99,1.28) Scott & Marrs 25.2

-0.21 (-1.57,1.15) Overall (95% CI)

Call for data

The draft review will soon be available at

www.cebc.bham.ac.uk/draftreviews.htm. Obtaining further suitable

studies will help increase the sample size and robustness of the

analyses. If you are aware of any additional data, or would like to

contribute feedback to this review, please contact Tamara Kabat at

the CEBC by email on T.J.Kabat@bham.ac.uk.

Preliminary results