Aug 11, 2011


By Steve Blight

Photo: Giant Hogweed

When I was a teenager, I was a fan of the English music group Genesis and was fascinated by the challenging lyrics of some of their songs. The Return of the Giant Hogweed was one of these songs, with the lyrics describing a bizarre tale of the takeover of the humanity in England by a plant – the Giant Hogweed.

While things didn’t quite turn out quite as badly as the story told in the song, it is true that the giant hogweed is a very nasty plant. The giant hogweed first arrived in Western Europe in 1892, when two European brothers went on a botanical expedition to the Caucuses region of Eurasia. Fascinated by the plant’s towering size and huge flower head, they brought back seeds of the plant where it became quite popular, spreading from garden to garden around Europe.

It was first brought to the United States in the early 1900s, and the first confirmed record of the plant in Ontario was in 1949. Since then, it has spread to many different parts of Ontario, with confirmed reports as far north as Elliott Lake. It has a scattered distribution across southern Ontario, including the Ottawa area.

Giant hogweed grows best in rich, moist soil and is most often found in the wild along streams and ditches. It also grows along roads, trails, forest edges and in fields.

The seeds are spread via wind and water, as well as by human activity, and can remain viable in the soil for up to seven years.

Giant Hogweed is a biennial or short-lived perennial member of the same family of plants as parsley, dill and Queen Anne’s lace. It produces low growing rosettes of very large leaves (up to 1m or about 40 in across) during the first year of growth. Its leaves are deeply incised, pointed and serrated. Normally in the second year, it grows a large flowering stalk, which may reach heights of up to 5m (16ft). However, it may remain a large rosette and flower in a later year. The flowers are large, umbrella shaped clusters, called umbels, up to 0.75m or about 30 in. across of small white flowers, which bloom from June-August and then set seed. A single giant hogweed plant can produce up to 100,000 seeds. Only flowering once, the plant dies at the end of the season when it flowers.

As an invasive species, giant hogweed crowds out native plant species that provide preferred habitat for native species of wildlife. But perhaps more importantly, its sap is extremely poisonous.

Like wild parsnip, giant hogweed sap contains toxins called furocoumarins. These toxins can make the skin very sensitive to sunlight and may result in severe burns and blisters. The sap can even cause temporary or permanent blindness if it comes in contact with the eye. Large, watery blisters usually appear 15 to 20 hours after contact with the sap and exposure to sunlight. Contact between the skin and the sap of this species occurs either through brushing against the bristles on the breaking the stem or leaves. Healing can take months or even years in severe cases, and leave potentially permanent scars. In the event of contact with the sap of this plant, the skin should be covered to reduce the exposure to sunlight and washed immediately and thoroughly with soap and water.

Control of giant hogweed is usually through the application of an herbicide like glyphoshate, by cutting its roots to kill the plant, or by preventing the seeds from spreading. Given the potential for serious harm, it is likely best to leave work with this plant to professionals. Care must be taken to completely cover up when working with the plants, avoid any contact with skin or eyes, and destroy any cut plant material.

There are two excellent fact sheets on the Ontario Invasive Plant Council website

www.ontarioinvasiveplants.ca on identifying and controlling Giant Hogweed.

Giant hogweed also bears some resemblance to plants like Angelica and Cow Parsnip, and the New York State Department of Environmental Conservation has an excellent page detailing the differences at www.dec.ny.gov/animals/72766.html

While this plant is indeed a nasty customer and intimate contact should be strenuously avoided, it doesn’t seem likely that the plant will take over the human race as described in the 1971 Genesis song. Instead, this looks like a battle that landowners and local agencies should be able to win.

 

Please feel free to report any observations to Lorraine Julien at This email address is being protected from spambots. You need JavaScript enabled to view it.  or Steve Blight at This email address is being protected from spambots. You need JavaScript enabled to view it.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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