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Struggling to deal with Japanese Knotweed in your garden? Scientists are testing 8 ways to control weeds


It has been growing uncontrollably across Britain since its introduction nearly 200 years ago.

But scientists have revealed that it is possible to control Japanese Knotweed after testing the most effective ways to manage the rogue plant.

in Evaluation Of eight different methods, experts found that glyphosate-based herbicides were the cheapest, most sustainable, and most effective when dealing with exotic species.

On the flip side, using ground cover mulches to starve weeds was the worst method tested, with the highest price tag and the most detrimental impact on the environment.

The findings come at a time when there are more than 50,000 Japanese Knotweed infestations across the UK, dominating parks, railways and wastelands.

Invasive Japanese Knotweed (pictured) is a known killer of other plant species across the UK

Japanese Knotweed is a known killer of other plants, as it releases chemicals that stunt their growth and prevent sunlight from reaching them.

How to spot Japanese nodes

Japanese Knotweed is known as a great killer of other plants across the UK.

To spot these invasive species, look for some key signs:

  1. Spade-shaped leaves
  2. Brown stems visible in winter
  3. Zigzag trunk structure
  4. White flowers in summer

Source: Japanese Knotweed Ltd

The weed can grow up to nearly 40 inches deep in soil and live up to 20 years, according to Pest Control Japan Knotweed Co., Ltd.

To discover it, gardeners should look for its identifiable sinuous stem structure and white flowers that bloom in summer.

Japan’s Knotweed Ltd said on its website:When allowed to spread, Japanese Knotweed can grow under footpaths, and buildings causing structural damage as it finds weakness within a structure.

As part of the latest research, several herbicides have been used to spray plants or surrounding soil, including brands such as Glyfos ProActive, Depitox, and Picloram.

Each of the eight methods took a different stance on how to use herbicides or ground-film covers, alternating in use at different seasons of the year.

Scientists also changed the The amounts of herbicides per time with glyphosate for example range from 37 lbs to 47 lbs (16.9 and 21.62 kg) per hectare.

More Physical techniques complemented some of the methods as well, including manual weeding as well as digging and pruning of each underground stem (rhizome).

The herbicide glyphosate is the cheapest and most effective weed control (file photo)

The herbicide glyphosate is the cheapest and most effective weed control (file photo)

In general, the most effective methods have seen glyphosate sterilization applied either in the fall or in the summer and fall.

Not only was this considered the most cost effective, but it was also less time consuming than other methods.

It also had the least harmful environmental impact with its low concentration of 37 lbs (16.9 kg) and 40 lbs (18.43 kg) per hectare.

Geomembranes have been said to be the most harmful due to many factors including the plastics needed to make them.

Researcher Sophie Hawking of Swansea University wrote in: Conversation: We found that the geomembrane cover is the most harmful. This was due to the production of the plastics needed for the manufacture of the geomembranes, as well as the preparation of the earth required for their installation.

We also found that the use of digging as part of a turfgrass management program was also less sustainable due to carbon emissions from the use of machinery.

There are over 50,000 known Japanese Knotweed infestations across the UK and the plant is notorious for its ability to spread and damage building structures

There are over 50,000 known Japanese Knotweed infestations across the UK and the plant is notorious for its ability to spread and damage building structures

In light of the current climate crisis, reducing greenhouse gas emissions is vital. As we aim to achieve net zero carbon by 2050 in the UK, we need to think carefully about the sustainability of the approaches we use to manage Japanese knotweed and other problematic invasive plants.

Control of Japanese Knotweed is now a legal requirement in the UK with its management costs estimated at £165m each year, according to Study 2010.

Although here, the plant can also survive harsh environments – be it on the side of volcanoes or in freezing conditions.

Japan’s Knotweed Ltd added: “Knotweed can reappear and grow back on its own at any time, but especially if the contaminated ground is disturbed.

When developing a site affected by Japanese knotweed, if due diligence and control of Japanese knotweed are not taken, developers risk legal action for professional negligence.

“Ignoring knotweed can cause regrowth during or after construction, showing through hard and soft landscape areas and even within the fabric of the buildings themselves.”

Top tips for protecting your property

Like it or not, knotweed can endanger any property across the country. Look at a map to see if you live in an area at risk of invasive plants.

Simply enter your zip code to check the number of confirmed infections within a 4km radius. The most affected sites are marked in red, orange, etc.

Legal implications surrounding Japanese knotweed

Since 2013, property sellers are required to determine if Japanese knotweed is present on their property.

Sellers: It is the sellers responsibility to check the garden for Japanese knotweed. Sellers must complete Form TA6, used for transfer, which asks for confirmation of whether the property has been affected by Japanese knotweed and, where it is, to provide a plan for its removal by a professional company

Buyers: If the property contains Japanese knotweed, it will be stated in responses to Form TA6. This may result in the mortgage lender asking for assurances that the plant will be eradicated before funds are approved. A plan drawn up by a professional removal company tends to be sufficient assurance.

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