Return of the giant hogweed

Moira Baird
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Above, the giant hogweed flowers from July to August. Below, the giant hogweed can grow up to 15 feet in height in the warmer climates of B.C. Top photo courtesy of Isabelle Simard, MDDEP; bottom photo courtesy of Invasive Plant Council of B.C.

Last year, the giant hogweed was a novel, troublesome pest found along a portion of the Virginia River trail in the east end of St. John's.
This year, it's the poster plant for invasive species in the province and right across the country.
Giant hogweed can grow taller than the average person, and the clear sap from its leaves and stems can burn skin, producing blisters and scars.
"Giant hogweed is not only a threat to biodiversity, it's a human health hazard," said Todd Boland, research horticulturist with Memorial University's Botanical Garden.
On Saturday - international day of biodiversity - Boland will explain the perils of allowing the giant hogweed to gain a foothold in the province during a 2 p.m. lecture at the Botanical Garden.
Boland is the Newfoundland representative on the Invasive Alien Species national working group. His lecture will kick off a nationwide series of similar presentations.
Giant hogweed is similar in appearance to cow parsnip, which is native to North America and is found mostly along roadsides on the Northern Peninsula.
"It's not easy to tell them apart,"?said Boland.
The leaves of a giant hogweed can grow several feet in length, and are pointier and more deeply serrated than those of cow parsnip. As well, the stem hairs are bristly rather than soft.
An impressive sight, giant hogweed flowers from June to August, featuring large, umbrella-shaped heads consisting of many small, white flowers.
The sap from cow parsnip is also phytotoxic, but it will only cause a rash. Giant hogweed sap is much more toxic.
Boland said it can take up to five years of diligent work to eradicate giant hogweed.
"One plant can produce thousands of seeds. The seeds can survive in the ground for a couple of years before they germinate.
"The big problem with that plant is it usually grows around rivers. It likes wet areas, and the seeds fall into the Virginia River and they'll just flow on down the river."
Travelling seeds can be a problem.
"There's instances where seeds have turned up elsewhere 10 kilometres downstream from where the darn plant was.
"So, it has potential to become quite a pest, if it's not nipped in the bud, pardon the pun."
Following an August 2009 Telegram story, the Botanical Garden received several calls, but the reported plants turned out to be angelica.
"It's an edible plant and there's absolutely no reaction to it whatsoever."
And unlike the giant hogweed, its stem is smooth.
Boland recommends not touching any suspected giant hogweeds - just send photos by
e-mail to jtboland@mun.ca so he can identify the plant.
The goal of the invasive plant campaign is to prevent giant hogweed from becoming the kind of major pest it is in Europe.
It arrived there in 1817 from the Caucuses and central Asia as an ornamental garden plant.
"It's a big, imposing plant."
A century later, giant hogweed arrived in North America.
"How it got to Newfoundland, God only knows. Presumably, it came in infected soil."
Boland said giant hogweed is a serious problem in British Columbia, where it can grow up to 15 feet tall along the coast, and in southern Ontario.
There's a small population in Quebec, and only one known location in both Nova Scotia (in Cape Breton) and Newfoundland.
Here, the plant can grow to six to eight feet tall.
So far, it doesn't appear to be present in New Brunswick, P.E.I. or the Prairies, but it is on their watch lists.
It can tolerate climate zones of five - such as Newfoundland - or warmer.
Invasive plants out-compete indigenous plants and take over an area. Because giant hogweed's deciduous leaves can span several feet, it shades neighbouring plants, which then die off.
In B.C., for instance, all the bare ground beneath the giant hogweed has led to soil erosion and the silting of streams.
"That could become an issue here because it's growing along the Virginia River," Boland said.

mbaird@thetelegram.com

Organizations: Botanical Garden

Geographic location: Virginia River, Newfoundland, St. John's North America Europe Asia British Columbia Southern Ontario Quebec Nova Scotia Cape Breton New Brunswick

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Recent comments

  • Gillian
    August 10, 2013 - 15:57

    We have approximately six hogweed plants growing in the ditches on my street in Flatrock. Can anyone tell me who I should contact to get rid of these plants? We have a lot of kids in this area and I am afraid they are going to get hurt by this plant. I am afraid to do it myself.

  • Andrew Sparkes
    July 10, 2013 - 14:15

    We or rather, my parents, who live on a bay off Lake Simcoe , had one of these giants spring up in the run off ditch just off the roads edge. It was bagged and taken away to be destroyed before any seeds were released. The root started re-growing but was successfully eliminated with "Round Up" so far it has not returned.

  • Gord Barnes
    June 21, 2013 - 12:17

    We spotted giant hogweed along a trail on Woody Island. People need to be educated and learn to identify this noxious plant and where possible, signs should be posted.

  • Glennis
    July 01, 2012 - 13:00

    It's June 2012 and I have just returned from Newfoundland. I am horrified at the amount of cow parsnip growing along the western coast of Newfoundland. In some areas there is a complete carpet of the young plants. The seeds would appear to be spread by cars since there are far fewer plants when you move away from the roads. One woman in St. Anthony said her young son had to be hospitalized because he suffered severe blistering after playing in cow parsnip for a short period of time. Some Newfoundlands refer to the plant as Hemlock, and pronounce it emlac. It looks as though it may be too late to control the spread of this plant. No one I spoke to in Newfoundland was aware of any eradication programme or even information or instructions concerning this problem.

  • chris
    July 02, 2010 - 13:31

    Well I came into contact with that cow plant on the northern pensinula a couple of years ago and the are was burning for a couple of weeks leaving small scars on my leg. While talking to a resident of the northern peninsula he showed me scars on his arm from the cow plant.
    Contact from them was bad enough I wouldn't want these other plants to take hold.

  • diane
    July 02, 2010 - 13:26

    I think you meant Caucasus , not Caucuses .

  • chris
    July 01, 2010 - 20:20

    Well I came into contact with that cow plant on the northern pensinula a couple of years ago and the are was burning for a couple of weeks leaving small scars on my leg. While talking to a resident of the northern peninsula he showed me scars on his arm from the cow plant.
    Contact from them was bad enough I wouldn't want these other plants to take hold.

  • diane
    July 01, 2010 - 20:13

    I think you meant Caucasus , not Caucuses .