Invasive Plants A 'Public Health Hazard' Across Canada

Written by Posted On Monday, 27 July 2015 12:22

Giant hogweed sounds like something from a Harry Potter novel, but you won't get magical powers from this invasive plant. Instead, you could get a nasty skin rash and be told -- like a Renfrew, Ont. women was this summer -- to avoid direct sunlight for as long as three years.

The CBC reported that Sherry Steeves was gardening when she was exposed to the sap from wild parsnip, a close relative of the giant hogweed. The sap created a condition called phytophotodermatitis, an extreme sensitivity to the ultraviolet rays of sunlight.

"Both giant hogweed and wild parsnip are noxious weeds that look alike and can cause a public health hazard," says Martin Neumann, manager of Parks Operations for the City of Guelph, Ont. The city removed 25 plants from a park this summer and asked residents to be on the lookout for them on their property.

The plants have been getting a lot of publicity recently in Ontario, with new reports each summer during the last five years or so. Relatively new to Canada, giant hogweed is present in New Brunswick, Nova Scotia, Newfoundland and Labrador, Ontario, Quebec and in B.C. in the Lower Mainland, Fraser Valley, Gulf Islands and Vancouver Island.

The Workers' Compensation Board of B.C. says giant hogweed was originally imported from Asia as a garden curiosity. It says the "plant hairs" can even penetrate thin clothing, and that that a worker in North Vancouver was burned by the plants through his clothing.

Giant hogweed grows as tall as 10 to 15 feet, with hollow stems that are two to four inches in diameter. When in bloom, it has white flowers clustered in an umbrella-shaped head that can be up to two and a half feet wide.

To view photos of giant hogweed, visit and tdc's FarmGate sites.

The City of Guelph's website says you can tell if a plant is giant hogweed by its tall growth and thick stem with reddish spots. "It looks like giant Queen Anne's lace or wild carrot but is considerably larger," says the Guelph website. "It is important to note that other plants in our green spaces look like giant hogweed as well. Angelica and cow parsnip have a very similar leaf pattern and flower…many farmers may be familiar with cow parsnip, which have been found in farm fields for decades."

Giant hogweed and wild parsnip are generally found along roadsides and railway tracks, in public parks and near sports fields and fence lines.

The plants have chemicals called furocoumarins that cause the interaction between plants (phyto) and light (photo) that induce skin inflammation, says Ontario's Ministry of Agriculture, Food and Rural Affairs.

While wild parsnip, also known as cow parsnip, can cause the nasty rash when exposed to the sun, giant hogweed can blister the skin so it looks similar to a third-degree burn, says the National Invasive Species Working Group.

You get it by brushing up against broken plants, handling the plant material or even by touching tools that were used to cut the plants. The toxic sap is the in leaves, stems, flowers and roots of the plants.

If you're exposed to them, you should wash your skin immediately with soap and water. If the sap gets into the eyes, flush with lots of water and put on some sunglasses. Keep out of direct sunlight and get checked out by a doctor.

To prevent burns from these plants, experts advise becoming familiar with the plants so you'll know them by sight, and teach children to recognize them as well. Your kids should be taught the dangers of poisonous plants and discouraged from picking wild flowers.

Back in 1971, Genesis wrote a song called The Return of the Giant Hogweed, calling the plants invincible. That isn't true, but if you find the plants on your property, most municipalities and agencies recommend calling in experts to remove them.

If you plan to remove them yourself, The National Invasive Species Working Group says giant hogweed only reproduces by seed, so if you prevent seed development you can keep the plants isolated in their original position. It says removing the plants in summer is not recommended because they are too large and there's too much dangerous sap. Instead, cut off developing flowers to prevent the plant from producing more seeds.

Wear goggles, rubber gloves, rubber boots and thick coveralls. It's best to do the job on a cloudy day. Wash your boots and gloves with soap, water and a scrub brush before taking off your protective clothing. You should shower and wash the clothes as soon as possible.

The best time to remove the plants is in spring, when the plants are small. Use a sharp spade or narrow shovel to loosen and uproot the plant and slice the roots a few inches below ground level. If there are seeds, take care not to spread them around. The plant material should be burned -- never compost it.

Make sure to monitor the area for several seasons to make sure the plant has been eradicated.

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Jim Adair

Jim Adair is editor of REM: Canada's Real Estate Magazine, a business publication for real estate agents and brokers. He has been writing about Canadian real estate, home building and renovation issues for more than 30 years. You can contact Jim at

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