Giant Hogweed shows up in Duncan

Nature Nugget – September 19, 2018

A member of the Board coined the name Nature Nugget to describe these little 5 minute topics we like to add to the evening.

But as it happens the name Nature Nugget was first coined 33 years ago by the Nanaimo Field Naturalists, fore-runner to the present Nature Nanaimo. We are proud to continue this tradition and acknowledge the history and dedication of those people who started the first group interested in nature in this region in 1985.

You may remember at our meeting last April I talked about the invasion started by Captain Walter Colquhoun Grant in Sooke in 1850; an invasion which we are still fighting nearly 170 years later.

Today I want to talk about another invasion; this one reputed to have been started only 80 years ago by an unknown perpetrator. But this one is dangerous.

The invasion of Heracleum mantegazzianum or Giant Hogweed.

Giant hogweed shows up in Duncan  

reported in the Globe and Mail, June 2018

Duncan’s Dian Tulip was shocked when she realized two plants she was nursing in her garden turned out to be giant hogweed; an invasive and toxic plant which can cause blisters, burns and even blindness.

According to the Nature Conservancy of Canada, giant hogweed is one of the most dangerous plants in the country. The exotic plant can grow up to six metres tall and is covered in clusters of white flowers. Its colourless sap is toxic, and when it contacts human skin and is exposed to sunlight it can cause blisters, burns and even blindness.

Tulip, a landscape gardener,  former florist, said the plants were growing next to some cacti she had planted this spring. She said that when the plants started to grow, she was curious as to what they were and allowed them to grow to more than a metre high before she finally identified the species. “I’ve been a gardener for a long time, but this is the first time I’ve ever seen one of these plants,” Tulip said. “It may have come in the soil with cacti, in the bark mulch that I have spread around the garden, or maybe it was something as simple as birds leaving the seeds in their droppings here.”  She has checked with her neighbours and none that she has talked to have noticed any giant hogweed plants growing on their properties. She and her husband carefully removed the plants using gloves and other clothes to keep the plants from contacting their skin and carefully placed them in garbage bags.

Tulip said she took them to the dump herself because she was concerned that city workers would come into contact with the sap if they were put in the regular road-side recycling. “Giant hogweed can be very prolific and their seeds can last for 10 years,” she said. “This is the time of the year when they start to bloom so we wanted to get the word out about these plants.”

Its leaves are deeply incised and stiff, dense and stubby. They can exceed 1.5 metres in size. The stems of the giant hogweed have dark reddish purple blotches on the stalks, and the plants have large white umbrella-like flower clusters.

Originally found in Ontario in Canada, it has now also been found in BC.  It spreads rapidly, thriving near streams, creeks, ditches, roads, and in vacant lots (areas that are moist or wet). It can  be found in south and central Vancouver Island, the Gulf Islands, and Greater Vancouver area.

Seeds can remain dormant in the ground for up to 10 years.

Control is best done in the spring, bagging flower heads tightly with all  the seeds, or using herbicides. Do not burn or compost. You must wear full protective clothing, gloves, hats and goggles before touching the plant.

Key Identifiers

• Up to 6 m in height
• Leaves up to 1.5 m across
• Flower head up to 1 m across
• Reddish-purple blotches and stiff hairs on stem

Giant hogweed has been mistaken for other species, especially other members of the carrot family, including;

Giant hogweed contains furo-coumarins (psoralens), which make human skin hypersensitive to sunlight, causing cellular damage at the surface. They absorb long-wave ultraviolet light and become photodynamic. Symptoms of phyto-photosensitization include serious and extensive weeping blisters. The lesions often occur in a line where the person has brushed aside the stems. The bullae can be massive and irritating, and brown pigmentation may remain for years after healing.

Nature Conservancy of Canada describes giant hogweed is one of Canada’s most dangerous plants.

The non-native plant grows up to six metres in height and has large clusters of white flowers at the top; its clear, toxic sap can cause rashes, blistering, burns and even blindness if it touches the body and is then exposed to the sun.

“Giant hogweed … poses a real human health concern,” the nature group said in a release in June earlier this year following the Globe report.

Dan Kraus, a biologist with the conservancy, said the invasive Asian species likely arrived in Canada in the 1940s as an ornamental plant. Often mistaken for the similar-looking cow parsnip, it can be seen growing in gardens, along roadsides, in ditches and on the shores of rivers and streams. “A single plant can produce thousands of seeds and it can spread quickly. The seeds are dispersed when they fall into rivers and streams, and can be dispersed short distances by the wind. Because it’s a tall perennial, giant hogweed can take over large areas along rivers and streams, shade out all of our native vegetation and actually nothing can grow under it sometimes,” Kraus said in a statement.

But simply touching the plant is not dangerous, experts say. It’s the sap that is problematic and thoroughly washing your body and clothes after exposure can prevent the toxic reaction.

You are encouraged to report sightings via the iNaturalist.ca app.

Worksafe BC has issued a special warning pamphlet on the plant.

In 2015, five children in England were reportedly burned in two separate incidents after coming into contact with giant hogweed in public parks. “In Europe, dense stands of giant hogweed along rivers have caused erosion and it has been identified as a serious threat to salmon spawning habits in Great Britain.”

Further info –

Ontario http://www.invadingspecies.com/giant-hogweed/

Nature Conservancy http://www.natureconservancy.ca/en/what-we-do/resource-centre/invasive-species/giant-hogweed.html

BC Invasive Species Council https://bcinvasives.ca/invasive-species/identify/invasive-plants/giant-hogweed