IS JAPANESE KNOTWEED DANGEROUS?

You’ve probably heard by now some of the horror stories of Japanese knotweed, (Fallopia japonica).

Structural damage, decimated property values and mortgage providers refusing to lend. These are all possible consequences of an untreated knotweed infestation.

Maybe you’ve heard about how the ongoing invasion of Japanese knotweed damages biodiversity by supressing native species.

Perhaps you’ve read about people being injured by other invasive species like giant hogweed (Heracleum mantegazzianum).

Nobody wants to see knotweed on their property for a number of very good reasons, but is Japanese knotweed dangerous? Could contact with it harm people or pets?

Well, the good news is that Japanese knotweed is non-toxic and perfectly safe to handle. Despite its fearsome reputation, it is completely harmless to humans and animals.

In fact, Japanese knotweed is edible! The young shoots can be eaten raw or made into pies, crumbles, pickles and chutneys, or any recipe which calls for rhubarb. The older stems which are too tough to eat can be made into syrup for flavouring soft drinks or cocktails. Flower buds can be used for fermentation, to make wine and beer.

Japanese knotweed has been used for centuries in traditional medicine. Known in China as Hu Zhang, the dried root is used to treat many ailments including jaundice, coughs, congestion, inflammation and snake bites. It is also gaining popularity in the world of alternative therapy, as it contains an anti-oxidant called resveratrol.

While the claims of snake oil manufacturers should be treated with caution, resveratrol is also of interest to the scientific community as an anti-inflammatory, cardioprotective and anti-carcinogen. Clinical trials are yet to be completed, however.

You can visit the Japanese Knotweed Agency Gallery here and see what Japanese Knotweed looks like through the 4 seasons to help you easily identify the dreaded weed at the earliest opportunity. And there’s a whole load of real-life photos taken by the Agency Surveyors across the UK, to give you a feel of how rampant this weed is and how it can literally grow anywhere.

If you are unsure whether the suspect plant or weed is indeed Japanese Knotweed of a kind, you can submit a photograph to us here at the Japanese Knotweed Agency and one of our surveyors will assess and confirm whether it is or isn’t Knotweed, typically within just a few hours. Use our free identification service here.

Electro-Thermal Treatment for Japanese Knotweed

CAPITAL PUNISHMENT FOR JAPANESE KNOTWEED HAS FINALLY ARRIVED

Manchester based Japanese Knotweed Agency launched in 2018 to support businesses, Local Authorities and Housing Associations, but ultimately to support Home Owners who are affected by Japanese Knotweed to understand the legal and financial implications of having a Japanese Knotweed issue.

The surprising fact is that very few have heard of Japanese Knotweed, and even fewer are aware that it is present in their garden or on their land as they could not identify the UK’s No.1 Invasive Weed, even though in 2022 we seen a massive rise in infestations growing well over 10 and 12 feet tall.

Herbicidal treatments still do have a lot of use in trying to bring this invasive weed under control, but what are the problems and longer-term effects of using chemicals to treat Japanese Knotweed, and how do they compare to the new Electro-Thermal treatment now available in the UK?

Killing Japanese knotweed

When it comes to ‘killing’ Japanese knotweed, treatment and eradication can be a tough task and take several years to get the weed under control and eradicate – but it is possible with commitment.

Herbicide spraying was the only available treatment for killing Japanese knotweed. However, it’s important to know that herbicide will kill most of the plant, but it doesn’t totally eradicate the plant’s rhizomes (extensive root system) in the ground. This means that future re-growth is technically possible if not managed.

Continued multiple yearly applications of herbicide can prevent the spread and growth of Japanese knotweed, but if you want the knotweed’s rhizomes (roots) completely removed from the soil – excavation was required. This was the way to ensure complete Japanese knotweed removal.

Herbicides that Kill Japanese Knotweed

Does Roundup kill Japanese knotweed?

Roundup, Gallup, Landmaster, Pondmaster, Ranger, Rodeo, and Touchdown are all herbicides recommended to kill Japanese Knotweed. They are all glyphosate-based herbicides and will somewhat prove effective in treating the troublesome knotweed, safe to say what the eyes can see!

The best time to spray the leaves of Japanese Knotweed with herbicide is late summer or early autumn. This is the period in which the plant is flowering and so the foliage conducts more nutrients to the rhizome to build food reserves.

About glyphosate-based herbicides

Glyphosate-based herbicides will kill Japanese knotweed, but be careful, since these are non-selective herbicides, they will kill whatever plants they come into contact with, whether that’s Japanese knotweed or your prize geraniums. For this reason, many gardeners don’t like using herbicides, but in the case of Japanese knotweed, it is one of the few really efficacious solutions.

Glyphosate is a translocated herbicide as opposed to a contact herbicide. While contact herbicides may appear to be effective against Japanese knotweed, they are in fact only killing its leaves and shoots. This is why it is best to use a glyphosate. As a translocated herbicide, glyphosate is taken partially down into the plant’s roots where it does affect the root system to some extent.

How long do glyphosate herbicides take to work?

Glyphosate-based weed killers available from garden centres will all have a harmful effect on Japanese knotweed. This is normally a slow process requiring at least three to four growing seasons to be effective, and hinder the growth of Japanese knotweed. Professional Japanese knotweed removal companies have access to more powerful herbicides which can reduce the removal process typically by half.

Are there any other chemicals that kill Japanese knotweed?

Japanese knotweed is also susceptible to other chemicals like triclopyr and picloram. However, glyphosate is often the preferred choice for domestic use due to its suitability for use near water.

A word of warning with herbicides

While herbicides are an effective means of killing Japanese knotweed, their use should be limited to areas destined to become lawns or flower beds, do not use herbicides on areas that will one day become your vegetable garden.

You should also be extremely careful of areas that have had herbicidal treatment and as a big safety rule, do not let children or animals anywhere near the treated area.

JAPANESE KNOTWEED OR NOT?
A GUIDE TO IDENTIFICATION

You may well be aware of the infamous Japanese Knotweed (reynoutria japonica or fallopian japonica) which has been causing headaches for homeowners up and down the U.K. If not, you should visit the Japanese Knotweed Agency Gallery here and see what Japanese Knotweed looks like through the 4 seasons to help you easily identify the dreaded weed at the earliest opportunity. And there’s a whole load of real-life photos taken by the Agency Surveyors across the UK, to give you a feel of how rampant this weed is and how it can literally grow anywhere.

Japanese Knotweed is believed to account for 98% of the Knotweed in the U.K. There are, however several other varieties at large in the British Isles.

Lesser Knotweed:

Known, confusingly, by several different names (Persicaria campanulata, Polygonum campanulatum, Polygonum campanulata, Reynoutria campanulatum), lesser Knotweed is not as invasive as other varieties, but is still a vigorous plant. Rarer in the U.K. than other species, it is more likely to be found in Scotland and Northern Ireland.

Plants grow to a height of 2-3ft (60-90cm). The stems do not exhibit the familiar “zig-zag” pattern of its cousins.

Leaves are elongated, rather than heart-shaped, and vary considerably in size, displaying a “herringbone” pattern of grooves and sometimes reddish veins. The underside is paler, with fine white hairs.

Around mid-summer, tiny white or pale pink, bell shaped flowers appear in loose clusters.

Dwarf Japanese Knotweed:

Dwarf Japanese Knotweed, (Reynoutria japonica Houtt, Polygonum pictum, Polygonum compactum, or Polygonum reynoutria), as the name suggests, is a smaller form of Japanese Knotweed, rarely growing to more than 3ft (1m). Although less invasive than standard Japanese Knotweed, this dwarf variety is present as both male and female plants so may set viable seed and lead to further hybridisation.

Usually appearing in late spring, its leaves are darker and more variable in form than japonica. Lacking the distinctive “heart” shape, they are more oval, with wavey edges and a leathery texture.

Stems display the distinctive “zig-zag” pattern and reddish colouration of its larger relative.

White or pale pink flowers appear in late summer, forming upright spikes which can darken towards red as they mature.

Himalayan Knotweed:

One of Britain’s rarer Knotweeds, Himalayan Knotweed, (Persicaria wallichii, also known as Aconogonum polystachyum, Reynoutria polystachia, Persicaria polystachya, Polygonum wallichii, or Polygonum polystachium) is most likely to be found in southwestern England. Although sometimes mistaken for lesser Knotweed, Himalayan Knotweed is much taller, rapidly growing to 6ft (1.8m). It is a hermaphrodite and can self-fertilise, leading to greater invasive potential.

Leaves are darker and more elongated than those of Japanese Knotweed, typically 4-8in(10-20cm) in length and tapering to a sharp point. Leaf shapes vary, some tapering to the base and others forming a more heart-shaped lobe.

The zig-zagging stems are hairy, and although some stems show a familiar pinkness, they are more likely to be green. A distinctive feature is the brown sheaf which is retained at the base of the leaf stem.

Himalayan Knotweed flowers between mid-summer and late autumn, producing white or pale pink blossom in open clusters around 8-14in (20-35cm) in length.

Giant Knotweed:

Closely related to Japanese Knotweed and broadly similar in appearance, Giant Knotweed (Reynoutria sachalinensis), is, as one might surmise, a much larger variety than its more common relative, growing 13-16ft (4-5m) high. It has a shorter growing season than japonica, appearing later in the spring and dropping its leaves earlier in the autumn. Male and female plant are present in the U.K. and Europe, meaning that this variety can spread by seed dispersal as well as via the rhizome.

Leaves are much larger than japonica, reaching 16in (40cm) long and 11in (27cm) wide, but retain an elongated “heart-shaped” form. They are wrinkled around the edges and have white hairs on the underside.

Dense clusters of creamy flowers appear in late summer and early autumn.

Bohemian Knotweed:

Bohemian Knotweed, (Reynoutria x Bohemica) is a hybrid of Japanese Knotweed and giant Knotweed which has only been classified as a separate species in recent decades. Bohemica grows to an average 8-10ft (2.5-3m), but sometimes reaches 13ft (4m). Both male and female plants have been seen in Britain and Europe. This means that bohemica can fertilise and set seed, potentially making it more invasive than the infamous japonica.

Leaves are larger than Japanese Knotweed, reaching 10in (25cm) long and 7in (18cm) wide. They retain the familiar heart shape, but are a darker shade of green and more crinkled in appearance.

Flowers appear in late summer and early autumn, and are pale green or creamy white.

If you are unsure whether the suspect plant or weed is indeed Japanese Knotweed of a kind, you can submit a photograph to us here at the Japanese Knotweed Agency and one of our surveyors will assess and confirm whether it is or isn’t Knotweed, typically within just a few hours. Use our free identification service here.

A NEW TYPE OF KNOTWEED?

Many people have been contacting us regarding a pink form of knotweed which has been causing some confusion amongst gardeners and property owners.

There are several species of knotweed which take distinct forms and appear in many sizes. Some are relatively harmless, but the pink variety is considered an invasive species by the U.K. government.

Pink knotweed proliferates rapidly, creating a thick carpet of vegetation which supresses the growth of other plants.

Although pink knotweed evolved in harsh, high-altitude environments, it is extremely adaptable and is happy growing in both boggy, wet ground and drier, sandy soils. Depending on local conditions, it can be either annual or perennial, and even evergreen in warmer climes.

IDENTIFICATION

It is distinct from Japanese knotweed in several ways:

Usually grows to only 6in (15cm) high

Spreads horizontally to about 5ft (1.5m)

Prefers wet ground, but will grow almost anywhere

Forms a dense ground cover

Smells of urine

Leaves are elongated and range from 2in in an annual to 11in in a perennial specimen. The edges are a dark red, as are the stems and the “v” shaped marking on the leaf surface.

Small, pink globular flowers, which protrude above the foliage.

If you are unsure whether the suspect plant or weed is indeed Japanese Knotweed of a kind, you can submit a photograph to us here at the Japanese Knotweed Agency and one of our surveyors will assess and confirm whether it is or isn’t Knotweed, typically within just a few hours. Use our free identification service here.

DEALING WITH IT

Pink knotweed can reproduce both vegetatively and sexually, depending on local conditions. Like the better-known Japanese knotweed, it spreads by extending new shoots from a large, underground rhizome. Unlike its Japanese cousin, it can also reproduce by setting seed.

It’s vigour and adaptability mean that it can be difficult to control or eradicate. Any small piece of the rhizome which is left in the soil can lie dormant for years before growing into a new plant.

There are three options for getting rid of a knotweed infestation:

Herbicide:

Chemical spraying will kill off the above-ground growth and slow the spread.

Excavation:

Digging out and removing contaminated soil should be undertaken by specialists, as small pieces of root can grow into whole new plants, and transport and disposal of the waste requires specialised licences.

Electro-thermal treatment:

A powerful electric current is sent through the plant, from the stem, through the roots and into the soil. This causes the water in the plant to vaporise, disrupting the plant’s tissues, and effectively removing any moisture the weed would use to grow rendering it in a dried/dead state. Unlike herbicidal treatments, this new electrical method gives immediate results and uses no harmful chemicals. The electro-thermal treatment because it uses up to 5000V spreads from the stem right across the vast underground root system and is ultimately the most effective treatment available in the UK. Whilst this treatment is fairly new in the UK, Prince Charles is said to own one and uses it on the Royal estates, and Transport For London (TFL) have used the machines with massive results throughout 2022.

Japanese Knotweed Agency are so impressed with the technology and results that we will start to offer this effective treatment in early 2023 direct to homeowners who are affected by Japanese Knotweed.

If you have any questions or concerns, please contact:

• contact@japaneseknotweedagency.co.uk
• Japanese Knotweed Agency, Hexagon Tower, Crumpsall Vale, Manchester M9 8GQ
• Freephone: 03335 777 888
• Monday / Friday: 9:00AM to 5:00PM
  Saturday / Sunday: 9:00AM to 5:00PM – by email or voicemail
  Public Holidays: Closed (Email only)

Is the invasive species in your back garden? Japanese Knotweed Agency map the areas in the UK most at risk from Japanese knotweed

Japanese knotweed is a lot more common in the UK than you might think – and it costs the UK economy over £40million a year.

The plant, native to Asia, was initially brought to the UK in 1850 in a box delivered to Kew Gardens and was much sought-after for its pretty flowers. However, its fast-growing roots led to a wild proliferation – and now the plant can be found all over the UK.

Bolton has been revealed as the Japanese Knotweed capital of the UK in 2022, with the North-West of England making up three of the top four most badly affected locations.

Bristol comes in second and St Helens in third, while Wales is another particularly hard-hit region, with three places in the top 10.

So, what are key attributes of Japanese Knotweed and where are the most badly affected areas in the UK?

Japanese knotweed can grow several inches a day

It hibernates through winter and reawakens in the spring and spreads rapidly, with its root network expanding at an alarming rate. By midsummer, it can grow by several inches a day, and can be identified by its creamy white flowers which bloom around August.

Each root can grow to be three metres deep and several metres horizontally, often piercing through foundations, driveways and walls and causing extensive damage.

In 2021, Dr Ross Cuthbert, of Queen’s University Belfast, led a project to analyse the economic impact of all the UK’s invasive species, and found that since 1975, the plant has cost the UK economy at least £41million a year.
The majority of [Japanese knotweed’s] economic impact is in house devaluation from when you have knotweed on the property, and also the cost of removing an infestation,

Japanese Knotweed Agency have released their National Register in 2021 and seen over 35,000 records submitted by surveyors, homeowners, members of the public and people who enjoy the countryside. That shows how many infestations have been registered in particular areas which you can search by the first part of your postcode to see what has been reported near you.

Bolton has 684 infestations within a 2.5-mile radius of the town centre, whereas Bristol has 475 and St Helens 441.

Streatham, in south-west London, is the only location in the top 10 in the London area, and came in at ninth with 300 logged infestations.

Rapid urbanisation and a defeatist attitude to the species were to blame for its increased prevalence in the North-West and Wales.
The plant had become such a scourge in these areas that many believed it was too prevalent to begin to combat.

Urbanisation helps spread Japanese knotweed

Increases in urbanisation have also seen more soil being moved from one site to another, taking the plant — which can regrow from a lone, finger-sized piece of root — to new areas which it then takes over.

I think the reason why we see it far more in cities is because there has been more and more human movement of soil. A lot of that goes back to the Second World War when there were huge amounts of materials being buried, moved around, bombed etc and obviously there is still a massive amount of the weed in London.

There is also a lot of it in Wales and the reason for this is that for many, many years, the attitude was, ‘well, there’s so much around that there’s nothing we can do about it’.

Also, because land values are quite low in the area there’s no financial incentive to fully excavate it as opposed to just using herbicides to keep it under control.
If there was a million-pound house in London we would likely say that the value of the property justifies getting rid of the infestation properly, which means digging it up. So that might be a ten grand fee for a £1,000,000 house. But if you did the same in, say, Swansea, that house might be worth £100,000 so the treatment starts to look quite expensive.

So, in these sorts of properties, you would just go for a herbicide treatment and control it that way. But controlling is not killing it and it is most certainly not killing it all which is needed to prevent it spreading.”

According to research, approximately one in 20 homes are currently affected by knotweed, either directly or indirectly.

By publishing the 2022 British Japanese knotweed hotspots we hope to raise awareness and encourage people in the area to be vigilant for signs of knotweed as the growing season takes off, so they can act quickly if needed.

Anyone living near or moving to one of these hotspots would be wise to check their garden carefully, enter their postcode into Exposed to find out how many known occurrences are nearby and if in doubt, seek expert help.

Japanese Knotweed Agency offer a free onsite survey that provides a substantial report highlighting where any crowns of the weed are, its age and route of growth etc, and also checks for up to 58 other invasive plant species found in the UK. There’s a full quotation included by one of their registered specialist firms that comes with an Insurance Backed Guarantee, and the Agency can also advise if you are able to make a claim against a third party for the recovery costs of the treatment and Insurance Backed Guarantee, and also claim compensation for devaluation, with a typical claim value well over £10,000

If you are a homeowner and have Japanese Knotweed on your property, get your free Knotweed survey today:

FREE JAPANESE KNOTWEED SURVEY – CLICK HERE

WITH summer on its way, experts are urging homeowners to look in their gardens to see if they have certain plants which can “damage” property and “devalue” it.

Buying and selling property is often a stressful time, which can be made even more hard when invasive plants are found in the garden. To help homeowners identify plants before purchasing a new home, or to solve current issues, Japanese Knotweed Agency have unveiled the most “common” plants which can devalue property by as much as 15 percent.

Japanese knotweed is an invasive plant which is identified by its creamy white flowers, bamboo-like stems and shaped leaves. It is the most invasive weed in the UK, infamous for its devastating ability to cause costly damage. Its roots can reach down to 10 metres underground, making it extremely difficult to eradicate, and the spread of the weed could damage pipework, pines and weaken building foundations.

Due to this, Knotweed is listed as a defect to the property by RICS Homebuyer Reports, with the potential to reduce the price of property by as much as 15 percent.

Alan Hoey, Managing Director at the Japanese Knotweed Agency said “It is really important to check yourself or get a professional in to check and take immediate and thorough eradication actions before it gets too late if you find you are affected by Japanese Knotweed.

“We highly recommend you seek professional help when removing Knotweed as they re-establish easily from even the smallest remains of the root system.

If your property is affected by Knotweed and you are the owner, Japanese Knotweed Agency offer a free onsite survey and full report, along with a quotation for a herbicide treatment plan and 10-year insurance backed guarantee by a professional and qualified partner firm.

Request your FREE Japanese Knotweed Survey and Report

Similar to Japanese knotweed, giant hogweed is invasive and can spread very fast. It is often spotted in July and can be identified by green stems with purple shoots and white flowers. The expert said: “Widespread really across the UK, especially found around rivers and ponds, its sap is phototoxic and can cause severe skin burns or scars under sunlight.

“Though not causing direct harm to the property, buyers may still refuse to pay a higher price if present because of its high cost of removal, up to £15,000.”

According to the experts, Ivy is also “dangerous to your house”, with a strong wall-climbing ability. It can cause wall cracks, damage the mortar and bring dampness into the home. “Unlike giant hogweed, English ivy could be removed with bare hands by peeling them carefully off the wall. “It is also possible to kill them by cutting their roots and letting them dry out.

“However, not all wall-climbing plants are harmful, such as Boston ivy, so we recommend consulting a professional before mistakenly cutting some beautiful and safe plants from your wall.”

While most trees cause no harm, the experts said large ones such as poplar, willow and oak can be dangerous if grown close to property.

Poplar trees have fast-growing root systems which can spread out to 40 metres and take up 1000 litres of water and nutrients from the soil. “They could live around 50 years and are harder to remove when their roots grow thicker and bigger as time progresses. Their age, soil type, location, depth all matter when deciding whether your tree is a problem. If grown too close to your property, they could lead to further risks or cracks in foundations, subsidence and other structural defects, potentially costing you £5,000 to £25,000 to repair.”

Another invasive plant which can spread seeds metres away is the Himalayan balsam.

It was brought to the UK in 1839. It grows up to two to three metres tall and has pink flowers in summer and early autumn. It can kill off other plants and reduce biodiversity by stealing lights, nutrients and water.

It does not have physical danger to humans but its significant ecological impact on nature and associated laws are not favoured by buyers.

So, it is recommended to keep this plant controlled or eradicated, and make sure it does not spread to your neighbours’ home as it can be illegal.