Local authorities should start using powers they have to make people clear Japanese knotweed from their land, Carmarthenshire councillors have said.

Some of them gave examples of how the invasive and fast-spreading plant was blighting their ward during a debate at full council.

Councillors passed a motion which said Carmarthenshire Council should start using so-called community protection notices (CPNs) to force landowners to eradicate Japanese knotweed where it was impacting on local residents’ quality of life.

The amended motion also called on the Welsh Government to urge other councils to consider taking similar action.

Cllr Rob James, whose original motion did not include the Welsh Government line, said there was a “forest of knotweed” behind Ysgol Heol Goffa in his Lliedi ward, Llanelli, with houses also backing onto it.

Residents’ homes had decreased in value by tens of thousands of pounds, he said, and some people struggled to get insurance.

Cllr James said knotweed, which was brought to Britain from Japan in the mid-19th Century, was also “causing havoc” in other parts of Carmarthenshire.

“I think there is an opportunity at least to look at the worst cases,” he said.

Cllr Shahana Najmi, who also represents Lliedi, said residents had been in touch with her too about knotweed.

She felt the Welsh Government should offer funding to landowners, some of whom might struggle financially, to remove the pest plant.

Cllr Gary Jones said Llangennech Community Council started clearing knotweed from a patch of land but he claimed it couldn’t get agreement from the neighbouring landowners – one of which, he said, was the county council – that they would get their knotweed-blighted land treated.

“In a couple of years this (knotweed) will be back,” he said.

Cllr Kevin Madge said knotweed had spread inland from river banks “at an alarming pace”.

He said a multi-agency approach was needed, involving Network Rail among others.

“There is no doubt we have got a major problem as far as Japanese knotweed is concerned,” said Cllr Madge.

Cllr Sue Allen said the worst knotweed she had seen was from the train from Swansea to Carmarthen and Whitland.

“It’s spreading into gardens – I feel very sorry for those people,” she said.

Cllr Alan Speake said the county council didn’t have sufficient funds to tackle knotweed on private land while Cllr Kim Broom said the authority did have a plan for knotweed on its own land as far as she was aware.

This was confirmed by cabinet member for public protection, Cllr Philip Hughes.

He said resources and costs would be involved if the council weighed in on knotweed on private land.

But he added: “It is something that the cabinet would, I am sure, be prepared to consider afresh.”

According to Welsh Government guidance landowners do not have to control Japanese knotweed on their land.

But causing it to grow, or planting it, was a criminal offence.

Furthermore the guidance said councils and the police could issue CPNs in instances where people were acting unreasonably and persistently in a way that had a detrimental effect on residents, such as the unmanaged growth of knotweed.

A Welsh Government spokesman said: “The responsibility for controlling Japanese knotweed lies with the landowner. We do not provide financial support specifically for its control but funding is available for publicly-owned areas where control of invasive, non-native species form part of a wider project.”