Giant hogweed: Toxic plant causing a stir in the GTA

TORONTO – Giant hogweed – a plant with toxic sap – is causing concern across the GTA.

Though recent media reports suggest that more of the toxic plants have turned up in the GTA, the fact is, it’s been here for a while.

A story that ran in the National Post in 2010 citing the spread of giant hogweed in the Don Valley area has resurfaced on the Internet and is causing worry for homeowners and hikers.

However, Ralph Toninger, Manager, Habitat Restoration at Toronto and Region Conservation Area said there have not been any more confirmed sightings of the plant.

“We haven’t confirmed new findings,” he said. “We’ve had quite a few calls as a result of the media attention that has taken place… But we’re not aware of any additional, new infestations or sightings on TRCA property.”

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The giant hogweed can be found across Southern and Central Ontario, south of a line from Manitoulin Island to Ottawa, no further than Kapuskasing.

In 2010, the plant made headlines and caused a “giant hogweed summer” said Danielle Tassie, Project Liaison with the Ontario Plant Council. There were reports of people being burned by the sap.

“It contains a toxin that can cause dermatitis, so what happens is if you touch the plant, you’re going to get the sap on your skin and then the skin needs to be exposed to sunlight to get a reaction,” said Alison Kirkpatrick, Terrestrial Invasive Species Outreach Liaison with Ontario’s Invading Species Awareness Program. And that’s when you’re going to get the blisters, burning sensation… A lot of people are cautious to approach the plant, but it’s when you come into contact with that sap.”

Though it may be easy to spot giant hogweed once it reaches full growth, the younger shoots may be a bit more difficult. (Courtesy of Danielle Tassie/Ontario Invasive Plant Council). Courtesy Danielle Tassie/Ontario Invasive Plant Council

Symptoms occur within 48 hours and produce painful blisters. Coming into contact with cow parsnip can cause similar reactions. The reaction varies from person to person and can last for months or years.

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There are several plants that resemble the giant hogweed, but they don’t grow as large in size. Some plants include cow parsnip, woodland angelica and Queen Anne’s Lace (also known as wild carrot). The white flower clusters resemble Queen Anne’s-Lace, but are more widely spaced and have a flower head almost one metre wide.

“It is a member of the carrot family,” said Tassie. “That’s why sometimes people will confuse it with Queen Anne’s-Lace, wild carrot… It’s thought to be brought here as an ornamental plant. The first recorded population is from 1949, so it’s been around for a while.”

“We get a lot of calls, but probably 95 per cent of the calls, 98 per cent of the calls we receive turn out to be cow parsnip or not actually hogweed,” said Toninger.

Though there have been no confirmed reports of the toxin causing blindness, Danielle Tassie, Project Liaison with the Ontario Plant Council said that there is concern.

“Even though there are no confirmed reports, there is a concern that this is not something you want to touch your eyes.”

Ecologically, giant hogweed threatens our natural environment. It is one of the first plants that comes up in the spring, shading out other plants and not allowing them to grow. Hogweed is found along riverbanks and floodplains and, if there is an infestation, natural plants die back in the winter and leave exposed shoreline, causing soil erosion.

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What to do if you find giant hogweed on your property

Due to the toxicity of the plant, do not try to remove it yourself. The Ministry of Natural Resources recommends hiring a professional exterminator to remove it. If you see it in the wild, you can contact the Invading Species Awareness Program at 1-800-563-7711 or visit their website

However, if you choose to remove it from your property, it is best to use protective clothing and dig up the roots, otherwise the plant may continue to grow. After digging up the roots with a spade, covering it with black plastic may help to smother any new growth. The best time to remove the plant is from late April to early May. Do not pick fresh or dried flowers off the plant, as that further spreads the seeds.

David Jones, Vice-President of Toronto-based landscaper The Gardener, said people should call professionals to remove the plant but if they choose to forgo the help, to be wary of spreading hogweed seed.

“The main thing you don’t want to do is spread the seeds,” Jones said. “Each plant can give off between 50 and 125,000 seeds, so if you were to spread those seeds, you’ll have a much bigger problem in subsequent years.”

If you do get any sap on your skin, wash it off well with soap and water as soon as possible and keep the affected area out of the sun. If a skin rash occurs, see a doctor.

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“The main advice is, if you think it’s giant hogweed, just stay away from it.”

For further information on the giant hogweed, click here.

— with files from James Armstrong

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