0 Gone But Not Forgotten - The real risks of Japanese Knotweed

JK knotweed jungleGroundkeepers know all too well the plight facing them when Japanese knotweed is discovered. Japanese Knotweed Control give us an update and the dos and don'ts of treatment.


The UK's last mild wet winter, coupled with this year's humid summer, has encouraged the growth of the plant which can grow up to 40mm per day. It can take less than 0.7g of rhizome (subterranean stem) - no bigger than a fingernail - for an infestation to take hold, resisting domestic weed killers and growing through bricks, mortar and tarmac in its path. Its far extending roots allow it to hibernate during winter and, although appearing dead above the surface, the plant is very much alive in the subsoil.

As one of the UK's first specialist remediation companies, Japanese Knotweed Control is leading a campaign to combat misinformation and introduce a higher-level national standard for the management of the destructive weed.

The public communications campaign has been nicknamed 'Gone But Not Forgotten' because one of the biggest challenges, besides getting rid of the plant itself, is the amount of misinformation and misconceptions that exist in the UK. Those misconceptions continue to damage the industry.

Over the last few years, the industry has seen an explosion of new specialists appearing daily. A quick Google search brings up thousands of firms, so how can groundkeepers distinguish between contractors that really are fit for purpose and those 'cowboy' contractors that are giving the industry a bad name.

JK Stem injection processWarranty & insurance

Dealing with Japanese knotweed is generally a case of remediation, not instant eradication. The long process of safely removing the plant can take some time, with treated Japanese knotweed taking years to fully biodegrade into the soil. In reality, without a proper warranty, insurance and long-term remediation strategy, your knotweed treatment can leave you just as much at risk as when you first spot the distinctive leaves.

Bona fide remediation firms will give customers the warranty and insurance that protects them throughout the remediation process and not give the plant a quick spray and tell them it has been eradicated.

Japanese Knotweed Control was the first company in the industry to offer an insurance-backed warranty on all its treatment options. All work undertaken is fully insured and underwritten by Lloyds of London specifically for the treatment of non-native plant species and carries professional indemnity cover for £5 million including structural damage cover.

JK Knotweed in flowerThinking long-term

There have been a number of examples recently where previously treated knotweed, in the process of naturally biodegrading, has been excavated and disturbed. Knotweed is safe to leave in situ whilst it decays, but if disturbed by being excavated, nodes of viable material could potentially re-infest or cross contaminate unless completely decayed.

Herbicide application remains the most cost effective treatment option and can be highly successful if the correct chemical is applied at the right dosage rate at the right time of year and the plant is left in situ to decay over time.

It is important to recognise that if any works are planned within the contaminated area then additional remediation will be necessary, this is especially important for large-scale sites that are being prepared for building works.

Remediation firms need to work with customers to understand the long-term use of knotweed infested land and explain the biodegrading process of knotweed beyond its initial treatments.

JK New shoots appearingShared project

When groundcare experts discover Japanese Knotweed, it's important that they select a remediation firm that will work together with them on a shared project.

Groundkeepers are a great source of local knowledge and this knowledge needs to be harnessed by contractors when drawing up knotweed management strategies. It's important that a strategy is formed not only on a treatment programme, but also what will happen in terms of planting after the knotweed problem has been removed.

Membership bodies

Choosing a remediation firm that is a member of a trade body provides customers the reassurance that the firm has been independently verified. Independent bodies such as the Invasive Non-Native Specialists (INNSA) are working hard to drive up standards industry wide.

INNSA was setup to provide minimum standards in the industry and to ensure customers are offered bona fide contractors. It can also provide guarantees that the work will be completed should the contractor go out of business.

New members seeking to join from within the treatment industry, as well as consultants and suppliers to the trade, are required to be BASIS-qualified and accredited to ISO 9000 and ISO 14001, and are subject to strict financial checks during an annual audit.

JK A knotweed stemUsing the Environment Agency Code of Practice as a base mark for the services provided, INNSA members will work within a framework of standards, designed to ensure customers are offered the right product and that the right service is delivered.

INNSA has recently re-launched its code of practice, the Invasives Code, which is regulated by the independent Property Code Compliance Board (PCCB). The Invasives Code requires firms to adhere to INNSA's demanding technical standards and sets out minimum warranty and insurance requirements, consumer service levels and compliant handling processes.

So, what can the industry do to combat the misinformation?

The management of an invasive species is a complex issue and it requires environmental professionals that work to strict codes of practice to deal with it.

Affiliated industries such as groundkeeping need to recognise the correct management strategies that are required to treat non-natives invasive species such as Japanese knotweed. Pitchcare professionals have a critical role to play in both helping combat the misinformation and driving up standards. Specifying INNSA membership and the Invasives Code as a requirement for choosing remediation firms will drive up standards and eliminate 'cowboy' contractors.

The Dos & Don'ts of Japanese knotweed treatment

  • DO contact a specialist and start a treatment programme as soon as you are aware of it
  • DON'T damage it! The rhizome is highly regenerative and will readily grow into new plants. Damaging the plant can knock it into dormancy
  • DON'T uproot it! The underground rhizome system can extend up to 7m from the parent plant, and reach a depth of 3m or more
  • DON'T compost live material! A piece of rhizome the size of a little finger can grow into a new plant
  • DON'T treat the plant at the wrong time of year. Herbicide programmes are only effective if they are undertaken during the growing season, which is typically during the months May - October but most effective after flowering
  • DON'T excavate previously treated land without consulting your remediation contractor first
  • DO make sure that any boots or shoes that have come into contact with the weed are checked and washed thoroughly to ensure that contamination isn't spread further
  • DO mark out and fence off to protect the area immediately. Having a fence will help minimise the risk of further contamination
  • DO recheck any previously contaminated areas for up to 2-3 years after removal, ensuring that no re-growth has occurred
  • DO appoint a qualified contractor who can implement a knotweed management plan
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