Module 5 Japanese Knotweed

Introduction to the UK

Japanese Knotweed is one of the most problematic invasive species in the UK.

It originated from Asia, specifically from China, Japan and Korea. It is now categorised as an invasive

plant in North America and Europe. The plant was first introduced by the Victorians as an ornamental

plant and as cattle fodder. It was first recorded from Kew Gardens from the early 1800s. The first

recorded site in the wild was in 1886, in Maesteg in Wales, and it was first recorded in Swansea

(Glamorgan) in 1902.

The first official complaint about the plant was made in Swansea in 1970; and today it is a problem in all

counties in the UK. In Europe only the female plants are found therefore the seeds are non-viable, every

plant as a result is a clone, making it the world’s biggest female biomass. Japanese knotweed is a

rhizomatous perennial (spreads by underground roots).

Identification:

Japanese Knotweed grows rapidly on thick reddish brown single hollow stems. The stems have purple

specks running through them and visible joints (nodes) up their length. When the plant is mature it

grows simple branches. The dark heart-shaped green leaves grow out alternately giving a zig-zag effect,

and can grow up to 8-10 inches long and 3-6 inches wide with a pointed tip. The plant flowers in the

summer with small green and white flowers on a loose panicle.

The reason for the plant’s rapid growth is due to the fact it thrives on disturbance. When the plant is cut

the discarded off-cuts (nodes or fragments of rhizome) can colonise within 6 days.

Figure 1 Flowers and Leaf of the Japanese Knotweed

Figure 2. A) In early Spring red/purple shoots appear B) Grow rapidly forming tall, hollow canes

C) Purple-speckled stems D) The core of a rhizome is dark orange/brown.

Figure 3 Picture illustrates that a Japanese knotweed can grow up to 2m or 7ft lateral growth. It also

shows the zig-zag leaf formation.

Figure 4 Leaf Shape - there are a couple of other similar species which are less common but still

invasive.

Figure 5 Root of the Japanese Knotweed.

Figure 6 Over winter dead knotweed stems and canes - can be undetected if cut down.

Figure 7 Growth of knotweed throughout the year

Benefits of the Japanese Knotweed

Although it is an invasive specie there are some benefits of the plant:

1. The flowers provide a source of nectar for the bees all summer long.

2. Presence in riparian habitats allows for cover for mammals such as badgers and otters, and also

for nesting birds.

3. Helps to stabilize slopes.

4. It is a source of food and medicine.

5. Used as a dye.

6. Can increase the diversity of habitats. (Pseudo-woodland habitat - urban)

Disadvantages of Japanese Knotweed

There is proof that the Japanese knotweed does have social and environmental benefits, however the

negatives vastly out-weigh the positives!

1. Out-competes native flora by shading.

2. Can grow through tarmac and concrete

3. Rhizomes spread extensively underground

4. Very hard to eradicate - expensive and time consuming, sometimes taking years.

5. Waste containing the plant is ‘controlled waste’ and has to be disposed of correctly by law.

Figure 8 Japanese knotweed shown coming through the skirting boards inside a house

Figure 9 Japanese Knotweed growing through concrete on a road

Costs related to the Japanese Knotweed

Japanese Knotweed cost over £150 million a year to control and clear in the UK alone. DEFRA in 2010

stated that the cost of a national eradication program is estimated at £1.56 billion.

Legislation

· Wildlife and Countryside 1981 Schedule 9, Section 14 states it is an offence to deliberately

cause the plant to grow in the wild.

· The Environmental Protection Act 1990 is another broad ranging piece of legislation that

singles out Japanese Knotweed for a special mention. Under the Act it places a 'Duty of Care'

on the land owner and anyone they employ to dispose of soil or other material

contaminated with Japanese Knotweed. Contaminated soil is classed as ‘controlled waste’

which can only be taken to licensed landfill sites who must deal with it in an appropriate way

(e.g. deep burying). There are only a limited number of landfill sites willing to take this

material and they must be informed prior to the material being taken to them. A Waste

Transfer Note is needed and extra charges apply.

CASE LAW- EA vs PJ THOMAS,

2002

CASE LAW- EA vs. D. Reed,

Surrey 2004

CASE LAW- FLANNAGAN vs.

WIGAN MBC 1995

• EPA 1990, £2000, no • EPA 1990, £4000, no • Council found negligent

waste management

licence

• Wildlife and

Countryside Act 1981,

£1000, knotweed to

grow in wild

• Legal costs, £1576

waste management

licence, burning

demolition waste

• Legal costs, £4764.66

• Lit fire to burn out

knotweed on a track

– allowed JK to grow

into a garden.

• Required to:

– construct new wall

– treat knotweed

– pay all costs and

legal fees

Figure 10 Legal cases of Japanese Knotweed resulting in prosecution.

Other pieces of legislation also cover Japanese Knotweed such as:

● TOWN AND COUNTRY PLANNING ACT 1990 - Adversely affecting the amenity of the

neighbourhood (Chapter 11, Pt VIII, para 215-219)

● PREVENTION OF DAMAGE BY PESTS ACT 1949 - Keep land free from vermin (Section 4)

● HIGHWAYS ACT 1980 - Encroachment onto a highway (Section 154)

DEFRA’s ongoing Review of Non Native Species Policy

• Monitoring and Risk Assessment awareness, educating, keeping up to date

• Remedy and Control (established species) practical measures, ownership of the problem

• Prevention (introduction and spread) practical measures, ownership of problem

“Prevention is the first and least costly line of defence”

International Legislation

RIO Earth Summit 1992

● Article 8 (h): Conservation and Biological Diversity

“Prevent the introduction of (to) control, or (to) eradicate those alien species which threaten

ecosystems, habitats or species”

Convention on the Conservation of European Wildlife and Natural Habitats 1979 (Berne Convention)

● Article 11 (2):

“Strictly control the introduction of non-native species”

● Article 22, Habitat Directive-

“ Ensure that the deliberate introduction into the wild of any species which is not native to their

territory is regulated so as to not prejudice natural habitats within their natural range or the wild native

fauna and flora and, if they consider it necessary, prohibit such introduction”

Knotweed on Development sites

This plant is obviously a bit of a nightmare for developers, quarries, councils and other landowners.

During the planning process it is the job of the ecologist to spot these invasive species (bear in mind that

you might not see it in the winter when it dies back!). The costs of dealing with the plant are high and

can take time to eradicate. If it is not eradicated then there is a danger that it will rear its ugly head iin

the future (see previous photos).

A good starting point if for the Planning Authority to place a Standard Condition for Planning

Permission on the development to ensure it is treated before works commence on site and to ensure

that the workers and vehicles on site do not allow the spread of the plant.

If Knotweed is noticed on a development site, then the planning officer should put a Condition onto the

planning permission. For example:

“Full details of a scheme for the eradication and/or control of Japanese Knotweed shall be submitted to

and approved by the Local Planning Authority prior to the commencement of work on site, and the

approved scheme shall be implemented prior to the construction phase.”

There are however many issues with the the control and eradication of the knotweed on development

sites, for instance - Who decides the necessary works? Who monitors the work? Will it have a high

success rate? Who decides when the knotweed has been eradicated and treatment can stop?

Treatment

Figure 11 Before and after treatment with herbicide

Non Chemical

There are a number of non-chemical treatments that can be used; however similar to Chemical

treatments it can take years to fully eradicate the Japanese knotweed due to the resistance and

extensive nature of the underground rhizome. It must be noted that if any part of the plant remains in

situ the Japanese knotweed will persist.

Mowing and cutting the plant down will lead to the plant becoming weakened and eventually will die

off. However, caution is needed because the plant can re-grow from tiny fragments so these need to be

removed, dried and burnt.

The plant can also be dug out from the root; however the feasibility of disposing of the plant is difficult.

Japanese knotweed can be thoroughly dried out and burnt, but in cases where the rhizomes have

excessively spread it may need to be dug up and taken to a landfill site or deep buried on site.

If the plant is being taken to a landfill there will have to be a license, this policy comes under the EPA

(1990) Duty of Care Reg. 1991, and specialist contractors can be hired for such jobs. Hazardous soil

disposal rates vary across the country from around £50/tonne – £150/tonne depending on the type of

contamination and volume. However, in the case where no license is held it is illegal to transport the

knotweed and it must be taken care of on site.

On site the weed can also be buried, in accordance with the EA Code of Practice. Before it is buried, it

must be treated once with a non-persistent herbicide, then deep buried within a protective membrane

with the top of the cell at least 2m below the finished height. After being covered by soil it must then be

covered with geotextile membrane and the EA must be informed at least one week before the works

commence. Burial pits can be used if necessary, they are impermeable and allow no moisture in to feed

the roots. These pits cause no environmental damage and one version is produced by WLS Water Lines

Solutions (Figure 12.)

Figure 12 Burial Pit with Water-Line’s DGW700

If the site is used for development or landscaping, specialist liners and covers can be placed to prevent

the spread of the knotweed and stop the knotweed from causing structural damage (shown in Figure

13).

Specialist liners:

Geo-Membrane

Geo-membrane works by reducing air and water, and diverts re-growth away from potential areas of

damage.

Root Barrier

Root Barriers are twin webs of geotextile sandwich and a copper foil sheet that releases chemicals to kill

off roots and prevent roots from penetrating the permeable barrier. The barriers usually have a life

expectancy of 50 years. An example of this type of barrier is RootX.

Figure 13 Liner to contain Knotweed

Eliminate Spreading

Procedures can be taken at an affected site to avoid spreading of the Japanese knotweed during site

clearance and construction phases, such as:

• Designate an entrance and an exit away from any potential knotweed remains.

• Carefully plan access routes within the site, to avoid spreading through human and vehicle

transportation.

• Utilises physical boundaries e.g. walls, fences

• Identify legal/political boundaries e.g. land ownership and who is responsible/who will be

affected

• Control and monitor waste and tipping

• Store plant remains together close to the Japanese knotweed sites

• Avoid riparian zones leading to watercourses

• Protect habitats, e.g. woodland, wetland from spread

• Provide services e.g. substations, pumping stations away from knotweed sites.

Biological Control

A plant eating insect Aphalara itadori (Psyllid) that specifically eats Japanese knotweed was released on

trial in a few locations in England and Wales in 2011 after extensive trials. The sites together with

control sites will be monitored for progress. For further details please read these articles:

http://news.bbc.co.uk/1/hi/8555378.stm https://www.cabi.org/projects/project/32999

Chemical

There are a number of chemicals that can be used for knotweed. Different factors may influence which

chemical can be used, and chemicals can range from non-persistent, semi-persistent to persistent. For

instance, if the area affected is near a watercourse then a non-persistent chemical needs to be applied

and the Environment Agency must be consulted.

Persistent/Semi persistent

Tordon 22k (picloram) is the most effective persistent/semi persistent chemical. It should be sprayed

between May and September, when the knotweed is in full growth. Tordon 22k (picloram) does have its

advantages and disadvantages, as you can see from the table below the disadvantages strongly

outweigh the advantages:

Advantages Disadvantages

Does not affect grass Cost is high

Direct to soil method Can not be used near water courses

Persistent for up to 2 years Can not be used near desirable vegetation

Can not be used under drip lines of trees

Spreads through soil especially on slopes

An alternative to Tordon 22k (picloram) is Garlon (triclopyr).

Non persistent

Roundup (glyphosate herbicide) is a well known non-persistent chemical which can be used near water

courses and can be applied when the knotweed is in full growth. Advantages and disadvantages do differ

from the persistent to semi-persistent chemicals.

Advantages Disadvantages

Can be used near water courses Less effective

It is selective and does not affect grass Requires repeated application over 3-5yrs

Not residual

2,4-D (Casoron, Broadsword) is an alternative to Roundup but it can be residual.

If spraying in or near water (within 7m) then you need to complete an ENVIRONMENT AGENCY WQM 1

FORM.

Shop bought chemicals

If the job is for a non-contractor then shop bought chemicals can be used. An example of this is

Tumbleweed. For the best results apply on a dry, warm day when rain is not expected and the wind will

not spread it. The advantages in this case do outweigh the disadvantages.

Advantages Disadvantages

Can be diluted or used from concentrate Can cause death to non targeted plants

Effective in the long run Requires repeated application over 3-5yrs

Cheap and readily available

Ready to spray; watering cans or sprayers can

be used.

Chemical - Stem Injection

Stem injection is the most effective method against re-growth of the Japanese knotweed and poses no

threat to the environment; its drawback is that it is time consuming. The best time of year to inject is

between June and September.

1. Firstly the stem must be cut just before a node, this is usually found 3-4 inches from ground

level. The cut off stem must then be placed on a plastic sheet to ensure the knotweed does

not spread, it will dry and then become non-viable, ideally it should then be burnt.

2. Drill or use a pencil to drill down into the stem that is still in the soil to create a hole inside

the stem, through the nodes. Water will seep out of the stem, allowing for the herbicide to

be injected into the stem.

3. Inject 5ml of herbicide into the node, the plants take up the herbicide within 20 minutes of

injection. Once this is done to ensure that it is fully protected attach cling film over the stem

with a rubber band (this also protects from rain.)

An Action Plan

When dealing with JK on site or in an area it is advisable to have an Action Plan that people can use.

Elements of this would include:

1. Promoting and encouraging a co-ordinated approach - Co-ordinate control, cost share

2. Identifying and treating sites - Criteria for treatment selection e.g. complaints

3. Preventing spread into unaffected areas – Survey, containment plan

4. Raising awareness and offering advice - Training

Grants Available

Woodland Improvement Grants- Forestry Commission

• No 2 Under managed Woodlands- species control

• No 3 Biodiversity- improvement non woodland habitats

Tir Gofal- Countryside Council for Wales

• Capital works for invasive species

Also several local authorities also have grants and projects available to tap into funding, advice and help.

JK Do’s and Don’ts

Knotweed DO’s

• Plan ahead and understand the problems

• Find out where your knotweed is

• Set aside a budget in the long term

• Look into grants, partnerships, cost sharing

• Use appropriate treatment methods

• Use trained contractors

• Be persistent and patient

Knotweed DON’Ts

• Ignore it, it will get worse!

• Use incorrect methods e.g. spray wrong time of year, using inappropriate chemicals (e.g.

diesel)

• Forget the law

• Use inexperienced contractors

• Expect treatment to work overnight

The Future

• Tougher legislation (e.g. via CROW Act, NERC Bill) to control movement, sale and spread of all

invasive, exotic, alien species at a national and international level

• DEFRA Non Native Review – an ongoing process involving many relevant stakeholders.

• Natural Control (in the long term) e.g. Psyllids Aphalara itadori - trial releases in Wales and

England

• Outside funding, e.g. Objective 1 from Europe

• Local authority action plan/officer

• Correct treatment techniques/methodologies used to ensure successful control in the long

term

• Increased awareness - political, trade, public

• Global warming - will this aid spread?

• The Horticultural Code of Practice - ensuring gardeners are aware of the plant and what to do

if it is present.

Further Reading:

Useful publications:

http://www.cornwall.gov.uk/environment-and-planning/trees-hedges-and-woodland/invasive-plants/ja

panese-knotweed/japanese-knotweed-publications/

http://www.cabi.org/japaneseknotweedalliance/ Legislation: http://www.nonnativespecies.org/index.cfm?pageid=67

What else can you find?