giant hogweed toronto

One of Canada's most dangerous plants is about to start blooming in Toronto

May has finally arrived, bringing the promise of warmer temperatures and another season of outdoor exploration opportunities. But intrepid hikers may want to hold off on switching from pants to shorts in the coming days, as a dangerous invasive plant may be lurking on Toronto trails and paths.

Known as Giant Hogweed or Giant cow parsnip, (Heracleum mantegazzianum), this pesky invasive perennial plant is a member of the carrot family with lacey white blooms that can grow to impressive heights.

However, using this plant to show off your Bugs Bunny impression or picking its white flowers would be a very bad idea.

It was the plant's aesthetic qualities that are believed to be responsible for its introduction to North America. Native to eastern Europe and western Asia, Giant hogweed is reported to have been introduced to Canada as an ornamental plant.

While it may be pleasant to look at, this plant could cause severe pain from just the slightest touch.

Coming into contact with the clear watery sap of Giant hogweed can result in severe dermatitis within 48 hours of exposure. This sap contains toxins that, once exposed to sunlight, can cause painful blisters on the skin that may produce permanent scarring.

Cases where the sap comes in contact with eyes are reported to cause temporary blindness. Unconfirmed reports of permanent blindness have yet to be verified, and the Province of Ontario maintains that such reports "cannot be substantiated by any existing research."

The outward similarity to plants like Queen Anne's-Lace creates dangerous opportunities for confusion among children.

Animals, including pets, are also at high risk of Giant hogweed exposure, as well as other invasive plants. In 2021, a patch of non-native burdock was reported to have caused several bird deaths on the Leslie Street Spit.

The plant is particularly quick-spreading and proliferates in areas like roadsides, ditches, streams, fields, and open woodlands, and now covers an area across southern and central Ontario, south of a span stretching from Manitoulin Island to Ottawa.

If you find the stuff on your property, the province advises hiring a professional exterminator to deal with the problem while limiting the spread of seeds. Experts say that now is the time to do it, too, as the plants are shorter and more susceptible to herbicides in late April and early May than in the warmer months to follow.

For those who insist on removing the invasive plant themselves, experts suggest wearing protective clothing, including eye protection, a disposable spray suit and waterproof gloves, as well as using a spade to distance oneself from the plant.

Transferring any sap from clothing is the biggest risk when trying to manage giant hogweed on your property, and spreading the stuff around your yard could pose risks for pets and wildlife.

Lead photo by

Scottish Invasive Species Initiative


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