Giant hogweed is an invasive plant species that is dangerous to human health and pets, as well as the plant ecosystem.
In City parks, this species is managed as a health and safety concern under Parks Hazardous Vegetation program.
Giant hogweed is native to the Caucasus region of Eurasia and was likely introduced to North America as an ornamental garden plant.
There are a variety of plants that can be mistaken for giant hogweed: cow parsnip, Queen Anne's lace / wild carrot or Angelica. The following information may help you identify this plant before you make a formal report.
How does the plant spread?
Giant Hogweed produces thousands of seeds, the majority fall to the ground close to the parent plant, but a large number can be easily spread along watercourses and by animals and people.
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Flower head
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Leaves:
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Other available resources to assist in identification of the plant:
Please familiarize yourself with the identifying features of Giant Hogweed and its common look-a-likes. Report any suspected Giant Hogweed growing in a park and in sight from maintained trails and paths and from maintained areas of parkland to City of Toronto, 311. Do not go off maintained paths and trails and off maintained parkland areas to look for Giant Hogweed. If the site has not already been identified as a location harbouring Giant Hogweed or a common look-a-like, 311 will submit a service request for a site inspection by Parks. In your report to 311, please name the park and describe identifiable features in proximity to the site to assist staff in finding the location of the vegetation of concern within the park.
If you wish to report suspected giant hogweed on private property see: Bylaw enforcement - long grass and weeds - natural garden exemptions - on private property
You can also report a sighting of giant hogweed using Ontario Invasive Plant Council mapping system.
What is Parks Forestry and Recreation doing about giant hogweed?
When a potential giant hogweed sighting is reported in a City park, Parks staff will inspect sites to obtain positive identification on the vegetation of concern. Should giant hogweed be present, the vegetation will then be assessed on a public health and safety basis. Following assessment, giant hogweed is then managed where it has been deemed hazardous and a public health and safety issue.
Will Parks remove the plant?
Giant Hogweed is removed when it poses an immediate health and safety risk to the public. In such cases, removal is done manually or with the use of herbicide that would be applied by licenced applicators and in accordance with all applicable legislation. Areas of Giant Hogweed that do not pose an immediate health and safety risk to the public are marked by caution signage.
How will Parks dispose of the plant?
Giant Hogweed is removed when it poses an immediate health and safety risk to the public. In such cases, removal is done manually or with the use of herbicide that would be applied by licenced applicators and in accordance with all applicable legislation. Areas of giant hogweed that do not pose an immediate health and safety risk to the public are marked by caution signage.
Where else is this plant found?
This plant is found in parts of Britain, United States, and Canada.
Giant Hogweed is present in a variety of locations in Southern Ontario including greater Toronto area. It generally establishes along roadsides, forest edges, and streams. For more detailed information on locations, see EDD map of confirmed sightings in Ontario and United States.
What will happen if I touch the plant?
Giant hogweed has a clear watery sap that contains toxins causing photodermatitis (skin reacts by becoming very sensitive to sunlight). If skin is exposed to the sap as well as sunlight, severe skin rashes, blisters, and even blackening of the skin can occur. Reddening and swelling of the skin can be noticed 24 hours after contact, further inflammatory reaction can occur after up to 3 days. Peak sensitivity occurs 30 minutes to 2 hours following contact. The reaction to Giant Hogweed sap depends on individual sensitivity, and in some cases effects can last for months, and skin can remain sensitive to UV light for years. Sap contact with the eyes can cause temporary and possibly permanent blindness.
The toxicity of the sap depends on the part of the plant that is touched. Sometimes just touching the surface of the plant may not cause a reaction, however sap can be picked up from the plant from brushing on the numerous blisters and hairs on the stems
My dog ran through a patch of Giant Hogweed, what do I do?
If it is possible that your pet has had contact with the sap from Giant Hogweed it is very important not to touch your pet with bare hands.
There is potential that you could get the sap transferred to your skin via your pet's fur. Using protective gloves, immediately wash your pet with soap and water and seek veterinarian help immediately. Seek medical attention if you feel you have been exposed.
What can I do to prevent contact with Giant Hogweed?
Be able to positively identify Giant Hogweed and to understand how it may be a risk to health and safety. Please heed any caution signage that may be posted for giant hogweed. Stay on maintained paths and trails and in maintained areas of parkland. Keep dogs on leash and do not touch any vegetation. Educate others.
Other Links to Identification Sources:
What should I do if I come in contact with giant hogweed?
What do I do if I find Giant Hogweed on my property?
Do not touch any of the vegetation and do not let any pets come into contact with the vegetation. Inform all family members accordingly. It is advised that you hire a professional to safely remove and dispose of the plants. Following removal, monitor the area for any signs of re-growth and contact the professional for follow up action as required should this occur.