A POISONOUS invasive weed that can cause third-degree burns has spread along the River Aire through South Craven and Keighley.

Giant hogweed grows up to 16ft high and a toxin in its sap makes skin super-sensitive to sunlight. Contact can can cause blisters, permanent scarring and even blindness if sap enters the eyes.

Its long-lasting effects can also mean victims have to avoid sunlight for years after contact.

Imported from southern Russia in the 19th century as a garden novelty, it is now spreading across the country, with a recent spike in reports of children and walkers being injured by innocent contact with Heracleum mantegazzianum, as it is officially known.

It has colonised riverbanks, verges and wasteland. and is now known to be established from Cononley right through to Bingley, said Aire River Trust spokesman, Kevin Sunderland.

“This is very bad stuff,” Mr Sunderland said. "We’ve found it at Cononley and it’s spread all along a stretch beside the trunk road at Steeton."

Mr Sunderland said a single plant could produce 80,000 seeds from its huge crown of tiny flowers.

“It’s the biggest herbaceous plant in Britain and they spread by air, but they really succeed when seeds get into the river and are carried downstream before settling in the muddy banks,” he added.

Giant hogweed needs to be destroyed before seeding takes place, and this can be done by high-strength weed killers or cutting it down.

“I’d appeal to people to help spot it as we need volunteers to monitor areas all the way to Bradford,” Mr Sunderland said.

An Environment Agency spokesman said: “We have been working closely with our partners to help to eradicate this highly invasive species from the Aire catchment.

“Our operational teams have been spraying the plant to prevent it from spreading further. Spraying is particularly effective when the plant is caught early."

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