Sustainable Japanese Knotweed Control


Sustainable control of invasive Japanese Knotweed

Swansea University bioscientists were recently invited to contribute a review article examining how Japanese knotweed can be better managed and crucially, in a more sustainable manner.

Invasive knotweeds have been shown to locally reduce plant and animal biodiversity through their prolific growth and consequently, UK legislation was introduced to minimise the further spread of this plant and manage it in the places where it was already found to be growing. Surprisingly, until last year controlling these plants was a topic of ongoing contentious debate as to what worked best, despite the management costs of knotweed in the UK exceeding £165 million per year.

Dr Jones said “until we published the first results of the world’s largest ongoing knotweed field trial last year, there was little data to support the use of different control methods. Our exhaustive integrated weed management (IWM) approach to testing has shown which methods work and those that don’t. We demonstrated that better knotweed control could be achieved with less herbicide and labour, delivering sustainable long-term control and management.

However, it is understandable how misconceptions around invasive plant management have arisen. In contrast to agriculture, where control is undertaken when the weeds are small and immature, deep-rooted invasive plants such as Japanese knotweed may grow for decades (or more) in the same place, making dislodging them far more difficult. Consequently, agricultural weed control methods and many herbicides often do not work when used against these invasive plants in the same way that they would when applied to conventional weeds.”

Prof Eastwood said “Prof Eastwood said “the physical size of the plant and the underground rhizome network pose a huge challenge for effective control. Our biological expertise was applied to target control to reduce herbicide use, CO2 emissions and labour costs. Sustainable control of invasive plants requires long-term planning and consideration of costs, such as fuel and labour. Non-herbicide control methods cannot currently be considered sustainable.”

As invasive plants such as Japanese knotweed have few weak points that can be exploited for effective control, this means that there is a limited toolbox of control methods available to use.

Based on the research conducted in partnership between Swansea University, Advanced Invasives and Complete Weed Control, only one herbicide is available to manage these plants effectively in the UK and the European Union (EU). However, this herbicide is the highly contentious molecule glyphosate.

Dr Jones said “we tested experimentally all practical knotweed control methods at large scale and for long enough that we can be confident which methods work and which do not. Herbicides are coming under legal and political pressure in the EU and North America; this is particularly true for glyphosate-based products. However, we need to be careful about removing this herbicide from use for controlling Japanese knotweed, as the only other viable option is complete physical excavation and disposal of the knotweed plant. Such remediation methods are more likely to spread knotweed plants and are more damaging than low-dose application of glyphosate as they disrupt soil structure and drainage patterns, irreparably damage surrounding habitats and are far more carbon and labour intensive – they are simply not suited for the strategic management of invasive weeds.”

Dr Jones said “we can do more with less, reducing our environmental footprint and the bill for householders, government and other stakeholders. However, as part of a mature debate, we need the right tools for the job and if we lose these, we will be fighting a losing battle with damaging environmental consequences.”

Advanced Invasives:

The full article is published in Outlooks on Pest Management and can be downloaded in the RESOURCES section of this website.

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