A forestry official confirmed two new findings of giant hogweed last week in Renfrew County, west of Ottawa. It has previously been spotted in Newfoundland, New Brunswick, Quebec, southwestern Ontario, Alberta and British Columbia. About 50 plants were spotted in Toronto’s Don Valley two weeks ago.
Contact with the weed’s clear, watery sap can be very dangerous, Jeff Muzzi, Renfrew County’s forestry manager and weed inspector.
“What it does to you is pretty ugly,” said Mr. Muzzi. “It causes blisters. Large blisters and permanent scarring. What’s left over looks like a scar from a chemical burn or fire.”
Even a tiny trace of sap applied to the eye can singe the cornea, causing temporary or permanent blindness, he added. The chemicals in the sap, furocoumarins, are carcinogenic and teratogenic, meaning they can cause cancer and birth defects.
Most provinces have not authorized official weed inspectors to destroy the poisonous plant because it does not impinge on agriculture.
Mr. Muzzi said he only began eradicating the plant because nobody else would. “It’s not really my job,” he said. “I just thought, somebody better take the bull by the horns here, ’cause this stuff is really dangerous.”
Giant hogweed is already rampant in parts of Europe including England, where the rock group Genesis wrote a 1971 ode to the plant and its “thick dark warning odour.”
Native to the Caucasus Region and Central Asia, it was brought to Europe and North America as a botanical curiosity in the 19th and 20th centuries and has spread rapidly. It typically grows on riverbanks, ditches and roadsides.
The risk of infection was so high, Mr. Muzzi wore a Tyvek suit, protective goggles, rubber gloves, “the whole nine yards,” to remove it, he said. “Which is really nice in 35-degree weather.”
The weed’s sap, which is found all over the plant, bonds chemically with human skin when exposed to sunlight and, within 48 hours, leads to inflammation, red colouring and itching, weeping blisters and eventually black and purplish scars.
“It’s those flower heads you want to get rid of,” Mr. Muzzi said. “I went out, suited up, cut all the flowerheads off and bagged them. Then I nuked the plants with Round-Up.”
Most susceptible to infection are gardeners, campers and children, who have been known to use the plant’s large, hollow stems as play telescopes or pea-shooters.
“If a person takes a weed-whacker to this stuff, they get the sap all over,” Mr. Muzzi said.
While the weed is on the federal government’s official noxious weeds list, there is apparently no national or provincial strategy in place to stop its spread.
Guy Baillargeon, a biologist with the Canadian Biodiversity Information Facility, called the weed an “emerging” problem, not yet a national one.
“Very few people are aware of it right now,” he added. “I am not aware that this species is on any provincial list yet.”
Mr. Baillargeon said a federal plan is in the works to deal with invasive species in general, but not hogweed in particular.
“I believe the plant has been here long enough that it would now be difficult to eradicate it,” Mr. Baillargeon said.
“So I don’t expect that things will happen overnight. But we need to talk about it.”
A 2005 study of the plant’s spread in Canada said it was likely to continue for the next 25 to 100 years “with worsening ecological, economic and health effects.”