Giant Hogweed creeping towards London area warns conservation authorities

The Upper Thames River Conservation Authority and Lower Thames Valley Conservation Authority are warning watershed residents to avoid contact with an invasive, toxic plant.

Giant Hogweed is spreading very quickly along rivers and streams, say the conservation authorities. The outbreak began several years ago along the North Thames River and has been moving rapidly down the river valley towards London.

The plant is being called a serious health hazard for humans. Its clear, watery sap contains toxins that can cause severe inflammation of the skin. People can get severe burns if the sap gets on skin and the skin is then exposed to sunlight. UV radiation activates compounds in the sap.

“If you find what you think is Giant Hogweed, do not go near or touch the plant under any circumstances,” says Brandon Williamson, land management technician for the Upper Thames River authority.

He says the issue is people getting sap on themselves by touching or breaking the stems, stepping on the plant, or even brushing against the leaves.

Symptoms occur within 48 hours and consist of painful, burning blisters that can cause severe irritation, dermatitis, and develop into purplish or blackened scars.

Depending on individual sensitivity, effects can last for months and skin can remain sensitive to UV light for years. Eye contact with the sap has been reported to cause temporary or permanent blindness.

“Hogweed grows along streams, ditches and roadsides, and is invading old fields and even woods,” says Williamson. “If you’re out for a hike or canoeing on the river, you need to watch out for it.”

Giant Hogweed can be much taller than a grown person, reaching up to five meters in height. It has large, flat-topped to slightly dome-shaped white flowers and seed heads and bumpy or bristly stems. The huge leaves are about one metre wide, and shaped like an exaggerated maple leaf.

More information is available at www.ltvca.ca.

Anyone who sees suspected Giant Hogweed on public property is urged to contact the local conservation authority or local municipality/weed inspector.

In the Lower Thames watershed, if you find what you believe is Giant Hogweed on private property, you can contact Ontario’s Invading Species Awareness Program to track the location of Giant Hogweed in the watershed and for assistance with plant identification and treatment options.

The Lower Thames Valley Conservation Authority can be reached at 519-354-7310 or by email at [e-mail].