Nasty, poisonous plant causes burns, blindness

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Nasty, poisonous plant threatens to spread across Canada. (HANDOUT PHOTO)

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The diameter of the noxious plant’s stem. (CNS)

It sounds like something out of a horror movie, but it's real, it's alive, and it's been spotted in southwestern Ontario, British Columbia, Quebec and the East Coast.

Could giant hogweed, a nasty and highly toxic plant that can cause chemical-like burns and permanent blindness, be on its way here?

So far, there have been no confirmed giant hogweed plants in Manitoba, said Invasive Species Council of Manitoba co-ordinator Cheryl Heming. That doesn't mean there won't be. "There is a possibility it could come here, and that's why we're on the alert," Heming said on Monday. "The usual format for invasive species is, a lot will come into southern Ontario or southern B.C., and given the ability to spread these species would come here afterwards."

The towering plant -- stalks can grow up to five metres tall -- originally hails from the Caucasus region and Central Asia. Over 100 years ago, it was brought to Europe and North America by well-meaning gardeners interested in its umbrellas of small white flowers. But the aggressive species has since run rampant in Great Britain and now threatens to spread across Canada.

Here's why it's bad: the plant's watery sap, loaded with toxic chemicals called furocoumarins, binds to human skin in sunlight, causing itching, oozing pustules and black and purple scars that can take years to fade. If even a teensy amount of sap ends up in the eye, it can burn the cornea, causing temporary or permanent blindness.

To make matters worse, the furocoumarins in the sap can also cause cancer and birth defects. And that sap is found all over the plant, whose hollow reddish stalks are often sought by children as peashooters or play telescopes. And the plant loves moist areas with turned-up soil, such as ditches, roadsides and abandoned urban lots.

Since national media outlets began broadcasting news about the giant hogweed's spread across Canada last week, the ISCM has received around 10 calls from people who thought they had spotted hogweed. Investigators were sent out to check but all the sightings turned out to be of a similar but much smaller species, cow parsnip, which is native to Manitoba. That plant is also toxic, though Heming notes that the risk of the public coming into contact with it is small.

Still, Heming urges the public to keep in touch with ISCM investigators. Last week the group posted a giant hogweed alert on its website, invasivespeciesmanitoba.com, to help spread the word. And if you see a plant that looks suspiciously like giant hogweed, don't touch it: call the professionals. "It would be great if people reported species they're concerned about, because then we can mobilize. That gives us an ability to do something about it," she said, noting the ISCM is readying a rapid-response program this year. "Our belief is that we like to stop the serious invasive species before they become widespread. That's what early detection and rapid response is about."

Still, it won't be easy to stamp out the plant's spread. "The only real success stories in controlling (invasive species) is controlling them at the point they are discovered," said University of Manitoba environment professor David Walker, who studies their impact on ecosystems. "Once they get a foothold, it's nearly impossible."

It's still not known if or when giant hogweed will flourish in Manitoba as it's difficult to predict how a species will take to an ecosystem until it happens, Walker said. But he notes that if it does, it won't be the first time a once-ornamental plant caused ecological, economic or health havoc. Dandelions and the dreaded weed purple loosestrife are also foreign plants brought over for gardens, he said.

"Most of the introductions we've had have been on purpose," Walker said. "People always want the newest flower in their garden. And a plant that may not be particularly invasive where it originally evolved, can become incredibly invasive... or not."

melissa.martin@freepress.mb.ca

Republished from the Winnipeg Free Press print edition July 27, 2010 A5