Japanese knotweed removal

Removing Japanese knotweed

If you are unfortunate enough to have Japanese knotweed you will be pleased to know that there are various options for control, management and/or complete removal. This page gives a brief overview of the options available and which is most likely to suit your needs and your budget.

Japanese knotweed is quite a dramatic plant: tall ‘canes’ growing rapidly from underground rhizomes which are a store of food over winter and that also give the plant its well-known ability to spread rapidly through the soil.

It is worth focussing on the rhizome network (which can spread several metres from the edge of a ‘stand’) as it is here where we need to concentrate when looking for effective removal/remediation. Any attempt to ‘kill’ or suppress the plant from above that does not also reduce the potential for re-growth from below is unlikely to provide any worthwhile medium to long-term success.

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Two main approaches to removing/managing Japanese knotweed

Option 1. Herbicide treatment.

The essential components to a successful herbicide treatment plan are firstly, to select a herbicide that is systemic (translocated through the upper parts of the plant to the roots/rhizome) and secondly to ensure that treatments are applied every year until you have at least two consecutive years of no growth. This is the reason why most herbicide treatment plans are presented as ‘5-year plans’ (up to 3 years spraying, 2 years monitoring) although you should be aware that individual projects can take up to 8 or 10 years before ‘Completion’. This tends to be with older, more mature stands of knotweed (with extensive rhizome networks), but in fact any stand of Japanese knotweed could prove difficult to control relative to ‘norms’ and nobody is really sure why.

The key benefit of herbicide treatment plans is economic but, as explained, they do require a medium to long-term commitment. We should also add that although PCA members will normally issue Guarantees against re-growth after Completion, this is not to say that the risk of re-growth of knotweed will not occur. Japanese knotweed has evolved to survive long periods of dormancy including that induced by systemic herbicides and for this reason this approach to knotweed control does result in certain restrictions to the use of the soil in treatment areas.

Option 2. Excavation of the Knotweed

Whilst the above herbicide strategy meets the needs of many, there are certain situations where Japanese knotweed, including its entire root/rhizome network, needs to be removed by excavation. Because this is normally a relatively expensive process, this option tends to be deployed only where there are development works planned. This could be anything from a major building project to a small extension or simple landscaping project (path, patio, driveway), but the necessity for a professional knotweed excavation/removal plan is the same: to manage the wastes arising as Controlled waste (unless the soil can be kept on site) and to ensure the full extent of the knotweed rhizome network is captured. The success of the excavation project also needs to be confirmed by at least two years of post-excavation monitoring.

Another benefit of excavation is the speed of remediation, but costs and some practical issues limit its popularity. Nevertheless, the fact that it can be deemed (as far as practically possible) a means of removal/eradication (rather than management/control) is attractive to some and may influence decisions where both options can be offered.

Of course, there is always the possibility to 'mix-and-match' these approaches - they are not mutually exclusive - and PCA qualified CSJK surveyors can advise on the best approach based on your individual priorities/needs.

Professional help is available

Managing, treating or removing Japanese Knotweed is not an easy job. It takes a lot of time and effort and can take years to effectively control the plant. There is however, help out there from qualified specialists.

If you are uncertain and simply want some help, most specialist PCA invasive weed members will be happy to offer advice over the phone and, if you have pictures, will be happy to look at them, and if you want a proper investigation and some consultancy prior to any treatments, then you can simply organise a survey.

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