War: The UK vs Japanese Knotweed (虎杖)

 

What do you know about Japanese knotweed? 虎杖 (いたどり)







My son’s book said: “イタドリおいしいのに、イギリスできらわれもの”

What does that mean?



Why do you think it's so hated in Britain?






  • Knotweed can grow 10cm a day in it’s peak months

  • They kill other plants by 1) growing tall quickly and using their leaves to block the sun, and 2) the fallen leaves release chemicals that stops other plants from growing

  • Now 5% of UK homes are affected by knotweed


Usually how do gardeners kill weeds?



Gardeners say Japanese knotweed is like fighting a hydra.

What do you think that means?









If you cut off the head, more heads will grow back.

Japanese knotweed can’t be killed by pulling it out or poisoning it.

When a volcano erupts and lava destroys all the plants, it will be one of the first plants to grow back. It can push through the lava.


The reason is the roots (called rhizone) survive deep in the earth and new plants can grow from it.


If you get a thumbnail-sized piece of root on your shoe, gardening tools or car tires, and walk to another area, the plant can regrow there. It only takes 10 days to grow into a plant.



How does Japanese knotweed affect homeowners?





  • In 2023 a man sold his home for £700,000 but a judge said he had to return £200,000 (¥35 million) because he didn’t announce the land had knotweed on it

  • A 4 bedroom home’s value fell from £305,000 to £50,000 (¥8.7 million) due to knotweed damage

  • If you sell your house, the official form includes the question: “Is the property affected by Japanese knotweed?”





The only way to stop it growing is to use the poison called Glyphosate but it takes 3 to 5 years and it may not work.
The World Health Organization thinks it is “probably carcinogenic” and Monsanto, its manufacturer, has lost lawsuits over its health impacts.

carcinogenic = “car-sin-oh-jeh-nik” = causes cancer

The US Environmental Protection Agency insists that glyphosate is unlikely to be carcinogenic.


How are banks affected by knotweed?




In 2012 the property assessment commission in the UK decided that any knotweed within a 7 meter radius was a threat to property values.

Many say the distance was too conservative but banks wanted help when assessing the value of a property.

Millions of homes were affected by this decision

 

If you discover knotweed on your property, what do you think you should do?

  • 7 metres

  • weed killer

  • remove soil

  • shoes

Some steps you should take:

  •  Immediately create a 7 metre “no go zone” around the suspect plant.

  • Do an initial spray with glyphosate-based weed killer.

  • Do not remove soil from the “no go zone” without permission from your local government

  • Any cutting should be done with very sharp tools or pulled out by hand to prevent pieces spreading to other areas

  • You must clean your shoes when you leave the area

  • If you cut down knotweed, you can burn it on site or bury it – 3 metres deep, covered with a root-barrier sheet – with permission from the Environment Agency.

 

 

Why do you think knotweed isn’t such a big problem in Japan?

 

In Japan there is a species of psyllidsih-lid” that eats (and kills) the plants.

These insects aren’t found in other countries to they are considering importing psyllids to battle knotweed.

What are the risks of doing this?


 

source:

  • https://www.theguardian.com/environment/2023/may/16/the-war-on-japanese-knotweed

  • https://www.dailymail.co.uk/news/article-2052337/Hertfordshire-couple-demolish-300k-home-rid-Japanese-knotweed.html

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