Japanese knotweed is a devastatingly invasive plant that can get homeowners and gardeners in trouble.
The fast-growing weed was brought to Britain by the Victorians as an ornamental garden plant and to line railway tracks to stabilize the soil.
While it is controlled by fungi and insects in Asia, it has no natural predators in Britain, where it can wreak havoc in gardens.
Now Environet’s invasive plant specialists have identified the UK areas suffering most from Japanese knotweed infestations.
Their results show that Bolton, Bristol, St Helens and Blackburn top the list of UK hotspots for the weed.
Researchers from Environet have identified which areas of the UK suffer most from Japanese knotweed infestations
UK’s Japanese knotweed hotspots
- Bolton, Greater Manchester (684 infestations)
- Bristol (475)
- St Helens, Merseyside (441)
- Blackburn, Lancashire (407)
- Capel Garmon, Snowdonia, Wales (398)
- Llanelli, South Wales (389)
- Cardiff, Wales (361)
- Rotherham, Yorkshire (306)
- Streatham, SW London (300)
- Nottingham (225) and Sheffield (225) =
Environet has developed an interactive map called Exposed: The Japanese Knotweed Heatmap that allows users to explore how many pests have taken place in their area.
“With the Japanese knotweed growing season now well underway, we’ve pulled data from our interactive online tracker, Exposed: The Japanese Knotweed Heatmap, to uncover the national knotweed hotspots for 2022,” it explained.
“Populated with nearly 55,000 known occurrences of knotweed, Exposed is the most comprehensive online record of knotweed infestations, charting the plant’s spread across the country.
“Simply enter your zip code to know the number of nearby sightings, with hotspots highlighted in yellow, orange and worst-case red.”
The data shows that Bolton is the area with the highest number of cases, with a whopping 684 infestations within a 4 km (2.4 miles) radius.
Bristol (475 infestations), St Helens (441 infestations) and Blackburn (407 infestations) are next on the list, followed by Capel Garmon (398 infestations), Llanelli (389 infestations) and Cardiff (361 infestations).
Finally, Rotherham (306 infestations), Streatham (300 infestations), Nottingham (225 infestations) and Sheffield (225 infestations) round out the top 10.
Japanese knotweed is incredibly durable and fast growing and can cause serious damage to buildings and construction sites if left unchecked.
Capable of growing 20cm in a day, it deprives other plants of their most important nutrients and water.
“In winter the plant dies back to ground level, but in early summer the bamboo-like stalks emerge from rhizomes deep underground to shoot up to over 2.1m (7ft) and stifle all other plant growth,” the royal explained Horticultural Society.
Luckily, if you suspect you have Japanese knotweed in your garden, there are several things you can do to get rid of it.
The data shows that Bolton is the area with the highest number of cases, with a whopping 684 infestations within a 4 km (2.4 miles) radius.
Bristol (475 infestations), St Helens (441 infestations) and Blackburn (407 infestations) are next on the list, followed by Capel Garmon (398 infestations), Llanelli (389 infestations) and Cardiff (361 infestations).
Biological methods include digging up the plant from the ground or removing all the leaves to stop the plant from photosynthesizing.
However, these methods can take years to take effect and you will need to check the plant regularly to remove new leaf buds as you see them.
The other option is a chemical method, which requires you to consult an expert.
“A glyphosate-based weed killer is the best option here, although keep in mind that it may take multiple applications for up to four seasons to completely eradicate Japanese knotweed,” advises Gardeners’ World.
“It is best applied to cut canes to allow the weed killer to thoroughly penetrate the plant and roots.”
Environet’s new interactive map comes shortly after a study found that invasive species, including the Japanese knotweed, have cost the UK economy more than £5 billion over the past 50 years.
Japanese knotweed is incredibly durable and fast growing and can cause serious damage to buildings and construction sites if left unchecked
While previous research has shown that invasive species can have major economic impacts, researchers at Queen’s University Belfast set out to understand just how much damage they have caused in the UK.
dr Ross Cuthbert, Research Fellow at Queen’s University Belfast’s School of Biological Sciences, said: “We found that the bulk of the costs came from direct damages, such as over the actual management of invasive species and particularly the prevention of future invasions.
“Disturbingly, we have also found that invasion costs are increasing rapidly over time and are likely to continue to increase in the future as more and more invasive species arrive in the UK.
“Again, these costs are grossly underestimated as very few of the known invasive species in the UK have reported economic costs (less than 10 per cent), indicating a lack of research efforts and reports of their adverse impacts.”
What is Japanese knotweed?
Japanese knotweed is a species of plant with bamboo-like stems and small white flowers
Japanese knotweed is a species of plant with bamboo-like stems and small white flowers.
The plant, native to Japan, is considered an invasive species.
Scientifically named Fallopia japonica, the plant was brought to Britain by the Victorians as an ornamental garden plant and to line railway tracks to stabilize the soil.
In Britain it has no natural enemies, while in Asia it is controlled by fungi and insects.
In the US, it is planned as an invasive weed in 12 states and can be found in another 29.
Incredibly long-lived and fast-growing, it can cause serious damage to buildings and construction sites if left unchecked.
The infamous plant strangles other plants and can kill entire gardens.
Capable of growing 20cm in a day, it deprives other plants of their most important nutrients and water.
