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Invasive weed management

Whether on a commercial site or in a client's garden, managing invasive weeds takes careful consideration. Unfortunately, there is no ‘silver bullet’ management or treatment we can suggest. It requires experience & knowledge to identify and put together comprehensive invasive weed management plans, normally including several years of bio-security protocols and rigorous programmes for their control.  

Whether you are a developer, a surveyor, property specialist or a landscape/gardener, we hope the information below (that includes Guidance Notes and other support pages) is helpful. 

However, if you are looking for qualified, experienced and professional help to assist with an invasive weed issue, you can easily find a local PCA specialist by following the search function below.

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Invasive species: why they need to be controlled

‘Alien’ invasive weeds & plants are unique in that they are capable of establishing in the wild and displacing native plant communities thereby disrupting, often quite dramatically, entire eco-systems (complex, balanced and relatively stable populations of inter-dependent species).  

The current list of non-native invasive plant species (NNIS) covers the following legislation:

  • Wildlife & Countryside Act 1981,
  • Wildlife & Natural Environment Act 2012 (in Scotland and Northern Ireland)
  • EU Invasive Alien Species Regulations - ‘species of concern’  

The PCA Invasive Weed Control Group was established in 2012 primarily to address the needs of the property sector for a professional, quality-assured service to manage one particular NNIS - Japanese Knotweed - thereby addressing the uncertainties that existed regarding best-practice and security of Guarantees.  Since those early days the PCA IWCG has embraced all aspects of invasive weed control and most of our members are regularly engaged to manage other species such as Giant Hogweed, Rhododendron, Himalayan balsam and bamboo in urban and ‘wild’ spaces.

Invasive Plant Species - The List >>

Initial steps & survey considerations

As is true with most challenges, the first task is always to identify the problem.  If you think you have an invasive weed species which needs confirmation or just want to have an overall site survey, some professional help is advisable.  All of our members will be able to help confirm the identity of most terrestrial species in the above list; some members are able to provide wider site ecology reports including aquatic species and, possibly, animal invasive species (Schedule 9: Part 1) or any plant/animal species listed as protected (Schedules 1, 5, & 7) under the Wildlife & Protection Act 1981.

Whatever the scope of the survey, from a Japanese knotweed inspection in a residential garden through to a full landscape ecology report, the key to each is good communication between client and surveyor/contractor.  You will probably find when you make an enquiry our members will have a series of questions about the site (e.g. Are all areas accessible? Can we take soil samples?).  This isn’t them being awkward - they are just making sure they can deliver what you need and that they have the right resources to conduct the survey safely and report on their findings including e.g. whether soil analysis throws-up any immediate concerns regarding waste disposal (if that is relevant).

Any report, whether it be from a PCA member or not, should clearly state your instructions and the scope and limitations of the survey/inspection.

Japanese Knotweed Management - Property Care Association

Managing & Controlling Japanese Knotweed 

The most well-known example of a non-native invasive plant species, primarily due to its frequency, wide distribution and prodigious growth rates is Japanese knotweed.  This invasive plant alone probably accounts for 90% of all enquiries, often associated with house buying/selling and/or land development.  

To find out more about managing Japanese Knotweed, Knotweed inspections and much more, click on the button below to visit our professional Japanese Knotweed section.

Japanese Knotweed Management >>

Other invasive weeds 

UK invasive species include nearly 70 plants ‘of interest’ under one piece of legislation or another.  But some are more likely to be found and/or causing problems in a residential setting than others.  Let’s have a quick look at the ‘top five’.  

+ Giant Hogweed

Giant Hogweed - Full blossom - PCA

Giant Hogweed, a member of the carrot family (umbellifers), was brought to the UK as an ornamental plant. Generally it grows near watercourses and in damp meadows, though it can be found on waste ground where conditions are right. It is a highly invasive plant that grows vigorously, the flowering spikes reaching upwards of 5m! Each plant can produce up to 50,000 seeds which can survive for over 10 years.

Giant hogweed is generally deemed to be ‘hazardous’ by skin contact due to a skin reaction which is triggered by sunlight (photo-sensitisation). Blisters occur 24 to 48 hours after exposure. Damaged skin heals very slowly, leaving residual pigmentation and affected areas can develop recurrent dermatitis.

A structured management & treatment program can achieve effective control over giant hogweed, but long-term monitoring is advised as the seed bank can take years to deplete and vulnerable sites may be re-colonised from adjacent areas.

There is a detailed Guidance Note on Giant Hogweed available to all.  Click on the button below to find out more.

Guidance Note: Giant Hogweed Management >>

CPD video on Giant Hogweed >> 

+ Himalayan Balsam

Himalayan balsam 3 - PCAHimalayan or Indian balsam is usually found on river banks and damp areas, though it is capable of thriving in most places.   This is one of the most widespread NNIS in the UK and some consider it to be semi-naturalised.

Whilst not seen as a particular problem in urban spaces, Himalayan balsam  causes a  problem for native species. Their flowers produce more nectar than native species making it more attractive to bees and other insects, luring them away from pollinating our native flowers.  Also, in common with giant hogweed, once established it shades-out other plants including those which nomally stabilise river banks so increases flood risks.

A structured treatment program can achieve effective control over Himalayan balsam but long-term monitoring is advised as the seed bank can take years to deplete and vulnerable sites may be re-colonised from adjacent areas.  A combination of hand pulling combined with targetted herbicide treatments early in the season is likely to provide the optimum approach to eradication but development sites may require some soil removal to deplete the seed bank before works commence. 

There is a detailed Guidance Note on Himalayan balsam available for all professionals. Click on the button below.

Guidance Note: Himalayan Balsam Management >>

CPD Video: Invasive weeds & the impact on the urban environment >>

+ Rhododendron, Japanese Rose and Cotoneaster Plants

Cotoneaster Plants - Invasive weed management - PCAThese plants are common garden/landscaping shrubs i.e. woody perennials which originate from Asia.  They have the classic traits of ‘invasive species’ - displacing native plant and animal communities etc. - but they are often overlooked in urban areas as they are so familiar as landscaping ornamentals..  Despite this they should be considered carefully in urban spaces too.  Once established they can spread ‘out-of-control’ through suckering root systems and seed dispersal.  At the very least making future management labour intensive and costly.

Of the three, perhaps the one most often ‘missed’ is Japanese rose as it can be confused with our native ‘Dog rose’..  Cotoneasters cause identification problems too as not all species/varieties are listed as invasive!  Fortunately, for those with a professional interest, the PCA offers a training course on identification for these and many other ‘Schedule 9’ plant species.

The collective experience of PCA members regarding effective management of these species (and the others above, and many more besides) is collected together in our publication “Practical Management of Invasive Non-Native Weeds in Britain and Ireland” a valuable resource well worth buying but unfortunately not available as a PDF download at the moment.

Invasive Weed Management Manual Page

CPD Video: Invasive weeds & the impact on the urban environment >>

Invasive weeds NOT on official lists

There are four particular un-scheduled ‘alien’ plants of direct concern to the PCA due to their impact in urban settings - bamboo and buddleia - and they are the subject of numerous enquiries so we include them here as worthy of mention..) 

+ Bamboo

Bamboo - growth near property - PCABamboos are members of a very diverse family of grasses, specially adapted to grow ‘woody’ stems.  Frequently planted as ornamentals, often as screening plants, many of the species selected have proved to be highly unsuitable for small (or even large) gardens!  So-called running bamboos can spread (through the soil initially) at alarming rates.  At the very least this presents management challenges for homeowners. These are ‘tough’ plants, but the cause of most professional enquiries is either encroachment (boundary issues) or damage to paved surfaces and even buildings (akin to Japanese knotweed).

CPD Video: Buddleia & Bamboo >>

+ Buddleia

Buddleia - growing out of a Factory wall - PCABuddleia is similar in many ways to all the woody shrubs/small trees above but is, if possible, even more common and widespread!  So much so that, despite only being introduced about 100 years ago, it could be considered naturalised. This is largely down to efficient seed dispersal and an ability to colonise masonry structures or other calcareous environments (e.g. derelict brownfield sites with concrete standings where it is a pioneer species).

There is little dispute that buddleia can and does cause lots of damage to brickwork (more-or-less ubiquitous in railway structures e.g. bridges, parapets, cuttings etc.). Consequently the PCA recommends it should be managed in the same way as many ‘scheduled’ invasive alien species. 

CPD Video: Buddleia & Bamboo >>

Link to ‘Manual’ publication

+ Poison Hemlock & Field Horsetail - Native Invasive Weeds

Posin Hemlock - Invasive weed management - PCAFinally, there are two particular native species which can sometimes be described as ‘invasive’ principally, as above, due to significant impacts on urban spaces, namely field horsetail and poison hemlock.  

Many PCA member companies offer services to manage Field horsetail, usually in a development context.  The challenges it poses are very similar to those of e.g. Japanese knotweed, but the PCA has not, to date, published any specific guidance.

Poison hemlock is, like Giant hogweed, a member of the carrot family and is capable of causing acute health effects by ingestion.  Otherwise, like all carrot family members, it can cause skin rashes sometimes severe due to allergic reactions.  It is included here as ‘invasive’ since it is widely reported to be spreading and over the last 5-10 years is commonly seen to dominate the vegetation on roadside verges and central reservations.  As part of our contribution to Invasive Species Week 2021 one of our PCA members created a useful video highlighting the characteristics and control methods for this and other umbellifers. 

CPD Video Invasive Weeds: from Hemlock to Hogweed >>

Other Considerations - Weeds Act 1959

Another area of weed control which some of PCA members and other professionals may be involved with relates to The Weeds Act 1959.  This Act names a short list of native species including ragwort, three species of dock and spear thistle. These are all known to be harmful when eaten by cattle and horses etc*.  Whilst there is a legal responsibility imposed on landowners to manage these weeds where they may affect fodder on agricultural land this is quite distinct/separate from the above legislation specific to non-native weeds.

*Poison hemlock is potentially harmful too but not mentioned presumably due to the fact that cattle etc. may avoid grazing on it as it gives off a pungent odour when the leaves are crushed. Nevertheless, hemlock is a lot more widespread now and some caution where it may affect grazing land seems warranted.  

Managing Invasive weeds

There isn’t  a ‘one solution fits all’ when it comes to invasive weed management. Certain invasive species such as Japanese Knotweed are notoriously difficult to control/manage, while others, especially those which can only spread via seed dispersal, can potentially be brought under control within 2-3 years.  Still others pose safety concerns (Giant hogweed, Poison hemlock) so that treatment programmes need to be conducted under strict health and safety protocols.

In many cases an invasive plant or weed can be effectively controlled by herbicide spray but the best long-term strategy usually includes some physical processes too (e.g. pulling, lopping or lifting plants before they flower, cultivation to stimulate growth, partial or complete root excavation).  

On commercial sites, where excavation is often considered as a 'fast-track solution' to remediate the site before building works commence, there will be a number of considerations about waste management (screening? Burial? Other contaminants? Disposal off site?) and these are all dealt with in a suite of documents regarding soil management and root barriers

More generally, for professionals that want to know more about invasive weed management options for a range of species, we recommend our book titled ‘Practical Management of Non-native Invasive Weeds”.   It lists 38 species, providing identification tips & descriptions, rapid response actions, preventative strategies, control measure and monitoring requirements of each.

For those who wish to gain more specialist knowledge and skills to manage and control invasive weeds, there are a variety of training courses available. Click on the button below to find out more. 

Invasive weed training courses >>

Non Native Weeds & Plants - Practical Management Booklet >>

Free training - Invasive weed related CPD videos

Using Professional Herbicides

Professional guidance on the use of herbicides to control invasive weeds such as Japanese Knotweed.

Find out more >>

Invasive Weed Control Group

A professional group developed to give homeowners confidence in finding invasive weed and plant related contractors, assessors & products that are right for the job.  Find out more about the group.

Find out more >>

Looking for a local professional to help manage an invasive weed issue?

If you are looking for a qualified professional to access an invasive weed/plant issue, members of the PCA’s Invasive Weed Control sector are able to provide site surveys and invasive weed management plans for a wide range of non-native invasive plants. 

However, not all PCA member companies provide full scope for all invasive weed/plant species e.g. some may not have the facilities to conduct aquatic surveys/treatments, so please check beforehand.

To find a specialist, simply use the search tool below.

Find a local invasive weeds specialist >>

Want to learn more about invasive weeds & plants?

For those interested in learning more about invasive weeds and plants, there is a variety of PCA training options for surveying professionals as well as technical/trade professionals. 

Use the search tool below to find available invasive weed related training courses or simply go to our training & qualifications section.  Alternatively, if you want to chat to someone, contact our training team on 01480 400 000 or contact them online.

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Professional Guidance

For those professionals looking for information, technical help and guidance towards and variety of property related problems, why not check out our 'professional guidance' pages.

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More about PCA Membership 

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