The top ten Japanese knotweed hotspots in the West Midlands have been revealed today.

Environet UK has identified Madeley in Shropshire is the worst affected location with 89 infestations within a 4km radius, followed by Shrewsbury and Birmingham.

Described by the Environment Agency as “indisputably the UK’s most aggressive, destructive and invasive plant”, Japanese knotweed grows rampantly along railways, waterways, in parks and gardens and is notoriously difficult to treat without professional help.

Japanese knotweed, or Fallopia Japonica, was brought to Europe from Japan in the mid-19C by German-born botanist Phillipp von Siebold who found it growing on the sides of volcanoes.

Initially lauded for its beauty and potential as animal feed, and it was so celebrated that in 1847 it was named the “most interesting new ornamental plant of the year” by the Society of Agriculture and Horticulture at Utrecht in Holland.

Knotweed's spread – through purposeful planting and it escaping – went undetected for years.

According to researchers at the University of Leicestershire, people sharing cuttings or disposing of unwanted plants was the "primary pattern of distribution” .

It was also spread through watercourses, and through the movement of soil for construction and road-building.

Knotweed expert Ann Connolly, who died in 2010, found one of the earliest examples of it being planted purposefully outside gardens was in Welsh coal-mining valleys in the 1960s and 70s as it was good for stabilising loose soil.

Table 1: Top ten Japanese knotweed hotspots in the West Midlands

No. Location No. of infestations within 4km
1 Madeley, Shropshire 89
2 Shrewsbury, Shropshire 55
3 Birmingham 51
4 Stoke-on-Trent, Staffordshire 48
5 Worcester 43
6 Stouport-on-Severn, Worcestershire 30
7 Wolverhampton 24
8 Coventry 23
9 Malvern Hills, Worcestershire 21
10 Leamington Spa, Warwickshire 10

Japanese knotweed can deter buyers, making a property difficult to sell and prevent a mortgage lender approving a loan unless a treatment plan is in place with an insurance-backed guarantee, thereby impacting a property’s value by around 10%.

Sellers are required by law to inform potential purchasers whether their home is, or has been, affected by Japanese knotweed, which can act as a deterrent even if the infestation has been treated.

Environet estimates that Japanese knotweed currently affects 4 to 5% of UK properties, wiping a total of £20 billion off house prices.

Homeowners who are concerned about knotweed infestations near their home could consider purchasing a specialist Japanese knotweed indemnity policy, which covers them for the cost of treatment, repairs, legal costs and any diminution of the property’s value, should knotweed arise.

Nic Seal, Founder and MD of Environet, said,  “Japanese knotweed has become a major problem in parts of the West Midlands, with notable hotspots in Shropshire and around major cities such as Birmingham and Stoke-on-Trent. It is impacting property prices, halting sales and causing a huge amount of stress and worry for homeowners.  

“At times such as this when the property market is slow and fewer homes are being bought and sold, it continues to spread unchecked. Anyone thinking about buying a property in the region, particularly in these hotspots, would be wise to check the number of infestations in the proximity of their postcode and consider instructing a Japanese knotweed survey on the property.”

In its native Japanese volcanic landscape, the climate and regular deposits of ash would keep knotweed plants small, while the plant survived thanks to energy stores in its deep root system.

But in Britain, without these impediments, it grows unabated.

And at its most prolific it can grow up to 20cm EVERY DAY.

It can even grow through concrete and tarmac and its roots can go down up to 3m deep.

There are no natural predators either meaning the weed can grow unabated, swamping other plants and preventing them from getting any light.

And while it does not produce seeds it can grow from minuscule fragments of rhizomes – the underground network of stems and roots – meaning it spreads easily .

Knotweed costs the UK economy £166 million per year for treatment and in home devaluations.

Last year, homeowners Matthew and Suzie Jones were told it would be cheaper to knock down and rebuild their £300,000 London home rather than try and treat their knotweed problem - that saw the familiar red bamboo-like plant grow through their floor.

And earlier this year, a man who murdered his wife before killing himself cited the weed that had blighted their West Midlands home as the cause for his mental distress.

In a suicide note, lab technician Kenneth McRae, 52, wrote: “I believe I was not an evil man, until the balance of my mind was disturbed by the fact there is a patch of Japanese Knotweed which has been growing over our boundary fence on the Rowley Regis Golf Course.