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What is Japanese Knotweed

 

 

Japanese Knotweed is a hardy bamboo like plant that was imported from Japan in the 1850's. This weed causes many problems on development sites and residential gardens.

 

It is a particular pest along waterways and railways where it colonises bare land very rapidly.

 

 

Identification of Japanese Knotweed

 

 

Japanese Knotweed is a tall perennial plant. This means that it dies back in winter and re-emerges in spring. The shoots start to emerge in late March / early April, are asparagus like and are a red-green colour. As it grows through the summer the red colour turns into red speckles on an otherwise green stem. At full height it can reach up to 3m.

 

The leaves are bright green and roughly hand sized in an almost heart shaped fashion. In September the plants develop small white flowers which in some cases can be so abundant that they almost completely cover some sections of the plant.

 

Around November time the plant drops its leaves and flowers. The hollow brown and brittle stem remains as a clearly visible indicator of where the plant stood in the summer. The next year the plant will re-grow from the same spot out of what is known as the crown.

 

 

 

How we treat Japanese Knotweed

 

 

The Invasive Plant Company offers many different types of remediation strategies for the eradication and management of Japanese Knotweed: The following shows a selection of those available, all of which are covered by an insurance backed guarantee.

 

Herbicide spraying program

 

A Herbicide Spraying Programme can provide a cheap, effective and simple strategy to treat Japanese Knotweed and is an ideal method for treating Japanese knotweed in parks, gardens and alongside rivers and railways. However, to be effective the treatment needs applications over a number of years away from any groundwork activities. As a result this method is not usually suitable for development sites

 

 

 

Excavation followed by stockpiling and herbicide treatment

This method is often the next cheapest alternative compared to spraying. Excavating the Japanese Knotweed material and stockpiling elsewhere on site allows for development in the originally contaminated area to proceed immediately. An added benefit of this is that the excavation process can stimulate growth in the Knotweed that herbicide treatment alone would not, allowing the treatment to be completed quicker.

 

As the material is excavated and treated on site it saves transportation costs, however does require adequate space to stockpile the material on site for a minimum of a 12 month period. Due to the nature of the pesticides used, the stockpile cannot be located near water.

 

Excavation followed by sifting and burial

The sifting process aims to remove all the Japanese Knotweed material through a combination of mechanised processes. This effective and quick method of dealing with the Japanese Knotweed on site means with most sites the remediation process can be carried out within a number of weeks.

 

This is also the most environmentally friendly of our treatment methods as it uses no persistent herbicides, however, it can be labour intensive.

 

Removal to Landfill

 

This method completely removes Japanese Knotweed material from site and is very quick to implement.

 

However, with the increasing costs of haulage this can be expensive for large areas of Japanese Knotweed and raises sustainability issues.

 

 

 

Reduced excavation and insertion of geotextile membrane

A reduced excavation vastly reduces the amount of material to be dealt with and hence the cost and timescales involved, although it does require careful liaisons with key stakeholders to ensure all contractors working on site are aware of the Japanese Knotweed excavation/geotextile works.

 

 

 

 

 

 

Japanese Knotweed and the Environment Agency

 

 

The Environment Agency's website also contains a guide for Japanese Knotweed remediation called The Japanese Knotweed Code of Practice. This offers practical advice on how to decide what is the best treatment program available for different situations.

 

http://www.environment-agency.gov.uk/static/documents/leisure/japnkot_1_a_1463028.pdf

 

It is not a legal requirement to follow the guidelines but often when dealing with Japanese Knotweed, contractors, consultants and developers will have to liaise directly with the Environment Agency or Local Authorities who will often use it as guidance.