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Japanese knotweed: Spot it, catch it, kill it

With thanks to Thurlow Countryside Management Ltd

Cue the relentless Japanese knotweed or fallopia japonica – the bane of homeowners, property developers and governments alike. So evasive and threatening to our eco-system, if you’re caught planting or growing it in the wild (why would anyone want to?) it’s considered to be a serious wildlife offence. It’s also a pain to get rid of and infests pretty much anything within its wake – including the rock hardest of structures. Even a herbicide solution, considered to be a cost-effective and sustainable removal method, means it can take 1 to 3 years to get to work effectively. No wonder the JK has a bad rep!

What is an invasive weed?
Weeds such as Japanese knotweed and its problematic foliage friend Giant Hogweed for example, are generally non-native plants, thought to be introduced by trade, an accident or botanical curiosity. Thank you very much Japan! They spread successfully with or without human intervention due to a lack of competition from native species. They can transform ecosystems, causing a variety of problems that seriously threaten native and endangered species. Some cause public health issues and due to extensive legislation, economic development can be seriously impacted. Enough of a reason not to grow it then? Other well-known invasive weeds are ragwort, thistle and docks for example.

In 1995, The Environment Agency estimated that the cost to eradicate Japanese Knotweed from the UK could be as much as £1.56bn."

What is its impact?

  • Affects the mortgage lending process
  • Negatively affects biodiversity and displaces fauna
  • Construction work cannot commence where they are present due to potential to cause damage to hard structures and public health issues
  • Successful at propagating – it’s estimated an area of developable brownfield land affected is approximately 800 hectares. 
  • In 1995, The Environment Agency estimated that the cost to eradicate JK from the UK could be as much as £1.56bn
  • It can cause extensive damage to hard structures.
  • Stands can increase by at least 10% in area each year

How does it spread?
Whereas Japanese knotweed only spreads via propagation of plant fragments, most other invasive weeds propagate via seed dispersal, although many use both methods. It prevents native seeds from germinating and forms a monoculture, adversely affecting biodiversity and displacing faun

What does it look like?
The seasons play a big part on its appearance during different points in the year, and tends to grow more between April and October., peaking in late summer.

Weeds develop red or purple asparagus-type shoots, which will turn to green bamboo-like stems that can grow up to 3m in height.

By early summer, expect that these plants will be fully grown with flowers blooming in late summer. Spot characteristics such as spiky stems, small, white and cream flowers, and flat green leaves with a heart/shovel like appearance.

The leaves fall to the ground and canes become dark brown in colour.

Remains dormant through the cold dark of winter.

What is the best way to get rid of Japanese knotweed?

It is your responsibility to eradicate it - kill it - control it, and prevent its further spread. For homeowners, who want a solution that doesn't cost the Earth, herbicide treatment, containing Glyphosate as the main ingredient and applied over three years to completely kill it, is highly recommended. Treatment should be started in the summer months. This method of removal brings benefits, such as:

  •   Normally lower cost
  •   Treatment in situ
  •   Overcomes boundary issues
  •   May qualify for land remediation tax relief
  •   Carbon emissions are minimal

Quick tips for choosing a specialist weed management company

Alternatively, you can enlist the help of a professional weed clearance company.

  • Survey for weeds on your site at the earliest opportunity and engage a specialist if identification is in any doubt
  • Ask for a GIS (Geographic Information System) drawing of invasive weeds on your site
  • Make sure their company is Amenity Assured and has robust environmental policies
  • Make sure your chosen specialist can demonstrate successful case histories with references for the type of work you want them to undertake
  • Insist on fixed costs and a fixed timescale with an agreed reporting procedure
  • Make sure they provide full warranty for eradication works and that it is backed by comprehensive insurance