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Where Did Japanese Knotweed Come From?

by the riverside Japanese Knotweed

Introducing Japanese Knotweed

Japanese Knotweed or Fallopia japonica is native to Japan, Taiwan and Korea. It is now widely seen across the UK as well as all over Europe and in North America, and is regarded as one of the worst invasive alien species.

In Japan the plant is known as Itadori, one interpretation of the name is that it means to “remove pain” which alludes to its painkilling and medicinal use. This is because it was originally used to treat a variety of ailments ranging from fungal infections, various skin inflammations and cardiovascular diseases, and still is today by some.

Where Is It Originally From?

Japanese Knotweed or Fallopia Japonica as the name would suggest originally originates from Japan, as well as other parts of East Asia such as Korea, Taiwan, and China. It is most commonly found growing on the sides of volcanoes usually at fairly high altitudes. In its natural habitat it shows its resilience and invasive potential, growing successfully on the scree and lava fields that line the slopes of Japan’s active volcanoes.

Japanese Knotweed in its native habitat, japan volcanoes
Japanese Knotweed in its native habitat.

In this environment the plants are much smaller than those that we see here in the UK, this is due to many factors like landslides, poor quality of soil and repeated coverings in volcanic ash from active volcanoes. As well as this Japanese Knotweed is also kept in check by the rest of its native ecosystem, other large species of plants and grasses such as Bamboo and Miscanthus out compete Japanese Knotweed. A range of plant diseases and soil fungi attack the plant and limit its growth.

Also, natural pests like the Aphalara itadori Psyllid which is like a plant eating lice contributes to its lack of growth in its natural environment to. These psyllids have now been brought to the UK and licensed by the UK Government for the biological control of Japanese knotweed in England; this was the first time that biological control of a weed was sanctioned in the European Union.

knotweed louse
This is the psyllid Aphalara itadori that keeps Japanese Knotweed at bay in Japan.

The Effects On A Non-Native Environment

In the places where Japanese Knotweed is classed as an invasive alien species, such as Europe and the UK, it grows at a lot faster rate and more dense. This is because it has none of its usual aforementioned factors effecting the plant as they would be doing in its native habitat, due to this it outcompetes any other plants growing near by.

No wildlife eats it and no other plants can compete with its exponential growth. This means the invasive weed has flourished across the UK, Europe and North America. Experts have estimated it costs the UK £166 million annually, as well as this it can knock up to 20% off your homes price and there are also cases of people being declined mortgages if Japanese Knotweed is present on the property.

It is relentless in its growth, growing up to an average of 10cm a day, sometimes more! It can grow completely in the shade and its root system can survive in temperatures up to -35 degrees Celsius. However it does not spread by seed, it spread via its Rhizome system (roots), to make matters worse a tiny fragment of rhizome can allow a new plant to grow. That’s why the destruction and movement of it is limited and rules are in place in the UK under the Wildlife and Countryside act. It also is very good at finding its way through cracks in concrete, tarmac and masonry and is known for damaging foundations and drainage systems.

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Japanese Knotweed taking over natural woodlands in the UK.

How Did It Get To The UK and Europe?

Between 1823 and 1829 Philipp Franz von Siebold was a Dutch botanist and physician was living in Japan, surveying plants and animals, von Siebold first came across knotweed on the slopes of a volcano in Nagasaki. In 1841 he returned to the Netherlands and set up the Royal Society for Encouragement of Horticulture, in the late 1840s he travelled to the UK and began selling the plant to high society figures and botanical gardens as well as it becoming commercially available in Europe. In 1850 Kew Royal Botanical Gardens began selling it to private companies and by 1869 became readily available to the UK public, with the plant mainly being bought by farmers for cattle feed.

From here the main pattern of distribution was through it being commercially available, this was way before its invasive power was known. It spread naturally, through water courses and it’s believed it was often transported in soil during construction or road-building. In a paper by Ann Connelly, an expert in various types of knotweed, she stated that in the 1960s showed the plant had been deliberately placed in Welsh coal-mining valleys as it was good for stabilising loose ground.

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Japanese Knotweed is still very prevalent by the side of water courses, as it can easily be spread by the moving water. However there are worries that it could be a flood risk.

How Can JKW Claims Help You?

If you think you may have a Japanese Knotweed infestation that you need help identifying or treating, then do not hesitate to get in touch with us, you may even be eligible to make a claim if the infestation is near your property or has encroached onto your land.

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