The UK’s worst Japanese knotweed hotspots revealed

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.

Nic Seal, managing director of Environet, an invasive plant removal company, said rapid urbanization and a defeatist attitude to the species were to blame for its increased prevalence in the north-west and Wales.

He said the plant had become such a scourge in the area that many believed it was too prevalent to begin to combat.

Urbanization helps spread species

Increases in urbanization 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,” he told The Telegraph.

“A lot of that, I would say, 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 I think 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.”

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