INNSA is proud to provide clear information for our members and their clients about invasive non-native species and their treatment. A wealth of information on the origins, implications and treatment of invasive non-native species can be found in this section

Where have these invasive plants come from?

Generally these plants have been introduced by the Victorians in their quest for exotic plants for their collections. They have since been allowed to escape the confines of the garden and become naturalised in the wild.

How do these invasive plants spread?

Himalayan balsam, Ragwort, Buddleja davidii, Rhododendron and Giant hogweed all spread via seeds, which can be carried through the air, downstream in watercourses or by flood waters, and which can remain viable for several years before germinating.

Japanese knotweed is mainly spread “vegitatively” by small fragments of the plant (known as ‘propagules’) and pieces of root (also known as ‘rhizome’) being moved from place to place. Tiny fragments of the rhizome as small as 0.7g are capable of re-growth.

In its establishment period after introduction in the 1850’s Japanese knotweed was planted on purpose to stabilise embankments and also used as fodder. Since then, spread has generally been caused by human activity, such as during the construction process – but can also occur by natural means during flooding and natural water flow.

Japanese knotweed (Fallopia japonica) can cross-breed with Giant knotweed (Fallopia sachalinensis), producing the hybrid Fallopia x Bohemica, which can be observed in the UK. Russian vine (Fallopia baldschuanica) can also pollinate Japanese knotweed and produce viable seeds (Fallopia conollyana), but these rarely overwinter successfully in the wild.

Why has japanese knotweed spread so quickly?

Japanese Knotweed in particular has been used as an infill shrub and to stabilise riverbanks, embankments and sand dunes. It was used by railway companies and by river authorities, which contributed significantly to spreading it all over the country.

The main vector of spread for Japanese knotweed in the UK continues to be human activity. Many homeowners are naïve to the problem and continue to weed, plant and dispose of Japanese knotweed incorrectly, causing further spread.

Fly tipping is a significant cause of the spread of Japanese knotweed, with unscrupulous contractors and irresponsible land owners seeking to circumvent the UK’s stringent disposal requirements.

Why is it problematic? Why should i be worried?

Japanese knotweed has no natural predators in the UK, and grows to the preclusion of all native species. It is a very hardy plant, which cannot be killed by simply cutting it down. The plant can cause damage to hard structures including walls, tarmac and other hard surfaces by exposing weaknesses; it can also block or damage man-made drains.

Japanese knotweed tends to exploit existing weaknesses in structures, and will usually penetrate through easy routes to sunlight, such as mortar between bricks, joins between concrete slabs and gaps between fencing or paving slabs.

Japanese knotweed has also been highlighted as being responsible for blocking natural drainage and reducing light levels on watercourses, as well as reducing biodiversity in natural ecosystems.

The root system of Japanese knotweed is extensive, and UK Environment Agency research has shown that it can extend up to 3m vertically down and up to 7m horizontally outward from the growth you can see above ground.

The plant has been known to enter a dormant state, often when it is overdosed with herbicide. It has been observed to re-grow from this dormant state after over twenty years in “hibernation”.

I have heard that there are biological control methods?

The UK government has funded CABI to release a species of Japanese aphid called the ‘Japanese knotweed Psyllid’ (Aphalara itadori) in several locations around the UK, starting in 2011.

However, this insect will not eradicate Japanese knotweed – although it should reduce the size and severity of infestations.

It is anticipated that plants that have been predated by the Psyllid will be more susceptible to chemical treatment and thus easier to eradicate.

Further research is being carried out by CABI in to additional biological control measures which could be put in to place in the UK in the future.

However, homeowners and developers alike cannot rely on these initiatives to eradicate your Japanese knotweed for you.

Am I legally obliged to treat ragwort on my land?

You are obliged to assess Ragwort on your own land, and you are legally required to remove or treat the plant in certain circumstances. For further information, please refer to DEFRA’s Code of Practice on How to Prevent the Spread of Ragwort

Under the Weeds Act 1959, landowners can be issued with a legally binding order to remove or treat Ragwort, or any of the other four species covered under the act (Broad-leaved Dock, Curled Dock, Creeping Thistle and Spear Thistle).

Am I legally obliged to treat any non-native invasive plant species that grow on my property?

For many species other than Ragwort, while there is no obligation to treat plants present on your own land, you have a legal duty under the Wildlife and Countryside Act 1981to prevent the plants from spreading in to the wild. The Environmental Protection Act 1990 makes it a criminal offence to dispose of certain invasive plants anywhere other than a Licensed Landfill site.

Furthermore, you can be found liable for damages in a civil court if you fail to prevent the spread of certain invasive species to neighbouring land.

Do I have to report any of these plants to the authorities?

We are unaware of any legal requirement to report the presence of any non-native invasive plant species to any authority.

Are there any changes in legislation likely to occur in the future?

EU directive on invasive species, due to be adopted in 2013

There is an EU Directive which may become enforced which suggests that landowners will be required to deal with invasive plants within their ownership

(Biodiversity strategy)

We understand that Japanese knotweed may in future be covered under the ‘Weeds Act’ which could make it the statutory responsibility of the land owner to treat Japanese knotweed within their site boundaries.

It is also possible that this change would mean that it would no longer be permitted to take Japanese knotweed off site to Licensed Landfill; therefore landowners will be forced to treat within their site boundaries.

What can I do if there are invasive weeds growing on my neighbours land?

The best thing to do is discuss the issue with your neighbour and come to an arrangement between you. If the infestation spreads over several properties, it is best to treat the whole area to achieve a long-term solution.

Many of INNSA’s contractors will offer solutions to allow you and your neighbours to share the costs of the treatment.

If the neighbour does not respond, then it is worthwhile documenting the infestation – especially if your land is currently free of invasive species.

INNSA members are able to provide a full survey service which will document the infestation, and provide a report which can be presented to the neighbouring land owner. Alternatively, this can be done by taking photographs and measurements yourself.

Can I claim the costs of treatment back on my house insurance?

Not as far as we are aware.

Is there any funding available for treatment of invasive species?

Land Remediation Relief is available to companies who pay Corporation Tax. Further information can be found on HMRC’s website.

We are unaware of any funding that is available to homeowners at this time.

Can I get a mortgage on my property when it has an infestation?

Always check with your mortgage provider first.

Each mortgage company has their own individual approach but, providing you have work carried out by a professional company who can provide the necessary warranties, we find that mortgage companies are normally prepared to lend on properties infested with Japanese knotweed.

However, some mortgage companies will not mortgage any property with (or near to) Japanese knotweed infestations. We have been made aware of cases where funding has been refused due to infestations 30m away from the property boundary (although such cases are, in our experience, rare).

We are aware of mortgages being refused due to other non-native invasive plant species (apart from Japanese knotweed) such as bamboo, but these cases are fairly rare.

How do INNSA contractors treat these invasive plants?

Japanese knotweed is best treated chemically by professionally trained operatives. If time constraints don’t allow for spraying, INNSA contractors have a range of different methods that eradicate knotweed and allow the site to be redeveloped in a short timescale.

The same general methodologies are available for treating most other invasive plant species, but will sometimes additionally include strimming, hand-pulling and/or the chemical treatment of surrounding areas identified as potential seed banks.

What is the quickest way of removing an invasive species from my land?

Excavation and removal from site is the quickest method of removing Japanese knotweed, but this is not suitable for many sites – especially private gardens.

The next-best alternative is normally a 12 month chemical treatment (although there are limitations to where this can be used).

How much will treating these weeds cost?

This all depends on the size of the infestation and the treatment method. Each treatment plan is tailored to each site.

Excavation and removal from site is normally the most costly option, and chemical treatment is normally the cheapest option.

Do you offer warranties / guarantees with your work?

All INNSA contractors offer a ten year Insurance-backed guarantee for commercial and domestic projects.This covers your site against unexpected re-growth for ten years after completion of the treatment, and also covers you in the event that the INNSA member should cease trading.

These guarantees cover works completed by INNSA members, and all works are carried out in accordance with the Environment Agency Regulatory Position Statement 178 on the treatment and disposal of invasive non-native plants, SEPA Guidelines, aswell as meeting with INNSA’s technical standards.

An Insurance backed guarantee is not a guarantee that Japanese knotweed will not re-grow; it is a policy which ensures that the customer has no cost implication in the event of future re-growth.

INNSA members should offer a warranty aftercare package as a priced option. This should cover return visits to site and any treatment required.

Insurance products are regulated by the FSA, and only apply in the event that the original contractor ceases to trade – at which point other INNSA members will carry out the required work, paid for by the insurance policy.

Can we bury Japanese knotweed on site?

Yes – you can bury invasive plant material on-site inside a root barrier membrane, but we do not recommend developing on top of this. Development on top of such a burial is allowed under the EA code of Practice, although conditions also apply. This is generally not practical for residential gardens.

It is also possible to move the Japanese knotweed to a Waste Management Area, on a layer of root barrier, so the JK is out of the way of where you want to develop/landscape and then continue a full chemical treatment plan there.

Can I dispose of invasive species myself?

We strongly recommend that you hire an INNSA member company who can provide you with the necessary advice, professional treatments, and an insurance-backed warranty/guarantee.

Certain invasive plants (found on this list) may not be disposed of in any local authority waste bin – and this may be seen as an offence under the Wildlife and Countryside Act 1981.

You are obliged to inform any waste disposal company before putting any of the plants on the list linked above in to a skip, tip or other such waste disposal facility.

When removing any material containing any plant matter from these plants from your property, the only place to which it can legally be taken in the UK is a Licensed Landfill site.

Japanese Knotweed will not compost and does not respond well to in-situ burning.

Can I treat invasive species myself?

We strongly recommend that you hire an INNSA member company who can provide you with the necessary advice, professional treatments, and an insurance-backed warranty/guarantee.

Digging up Japanese knotweed roots (rhizome) will often actually stimulate increased growth, and risk contaminating other areas and causing new infestations, so we strongly caution against it.

Cutting and pulling the plant from the ground is not advisable as this can also stimulate new growth, and the material arising can potentially cause new growth. Such material classed as Controlled Waste and is subject to specific waste regulations.

Giant hogweed poses a threat to human health, and contact with the plant can cause skin irritation, chemical burns and even blindness.

Chemical treatment using domestically available products may be effective with repeat applications – probably over several years with multiple sprays per growing season. However, if treatment is not carried out properly, following the relevant legislation, you run the risk of making the problem worse.

When is the best time to treat an invasive species?

Certain herbicides (non-residual foliar-applied herbicides) are absorbed through the leaf of the plant and therefore require leaf cover to work. Residual herbicides have been proven to work over winter (although there are limitations to where these can be used).

Scientific data suggests that the application of non-residual (Glyphosate-based) herbicides to Japanese knotweed works best during senescence when the plant is actively storing nutrients for over winter. Autumn applications often prove most effective.

For all invasive plant species, we would recommend starting on site as early as possible no matter what the treatment, as this can help to prevent the spread of the plant during the growing season.

Mechanical treatments are effective all year round.

How many visits will it take to eradicate the infestation?

This depends on the method of eradication being used and the size of the infestation. Sites near to watercourses or adjacent infestations may require on-going site monitoring and treatment to guard against repeat infestation from outside sources.

INNSA members can offer a series of revisits to your site to check for regrowth.

Can you kill Japanese knotweed with one treatment?

In certain situations it is possible that a single chemical treatment (either foliar applied or direct injection) can kill Japanese knotweed. However, it is not advisable to expect an instant eradication – invasive species specialists should always explain this to the client.

We would always recommend a follow-up treatment strategy which allows for the contractor to return to site and monitor progress.

INNSA members will not promise instant eradication, as this devalues the service that we provide and undermines the basic principles of Japanese knotweed eradication.

Are the chemicals used harmful to children / animals / humans?

Detailed information on pesticides is contained in the data sheet provided by the manufacturer, which is normally available on their website. The manufacturer is the definitive source of information regarding any pesticide.

Plants from areas treated with herbicides should never be eaten or otherwise consumed.
It is not advisable for humans, dogs, cats or other pets to be within treatment areas during spray works, however, once the spray has dried onto leaf the risks to human health are normally minimal.

In all cases where chemicals are to be used, contractors should always produce a detailed HSE and COSHH risk assessment for the chemical before it is used.

Can my gardener spray the plants instead?

Some Landscape companies have the required license to spray chemicals however very few have the required experience to deal with JK and other more problematic invasive species, and such contractors are rarely able to offer warranties and insurance-backed guarantees on their works.

Will invasive plants grow back after the treatment?

If treated with non-residual chemicals, Japanese knotweed will typically require several repeat treatments over a 2-5 year period to fully eradicate the problem. Otherwise, using foliar-applied residual chemicals can be very effective, and can normally kill Japanese knotweed in one season.

Other invasive plant species will require treatment lengths that vary between twelve months and up to five years.

As many invasive species spread by seed, it is possible for your site to be re-infested even if the treatment has been infested – and this is also true of sites where Japanese knotweed is present on adjacent sites, as well as sites next to high-risk areas such as railway lines and watercourses.

Any INNSA member will be happy to provide further information on the treatments that they offer, as well as providing you with a recommendation for the most appropriate treatment for your site.

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