INFORMATION NOTE
GIANT HOGWEED           

July 16, 2010

 

1. What is it?
Giant Hogweed is an invasive perennial known for its enormous size. This
species usually grows from 2.5 to 4 metres (8 to 14 feet) high with leaves up to 1
metre (3 feet) in breadth. It has thick, 5 to 10 centimetres (2 to 4 inches)
hollow stem. Its stem and the undersides of its leaves are covered in coarse hairs.

Its large, umbrella-shaped flowers are white in colour and can be more than 30
centimetres (1 foot) in diameter. The seeds of Giant Hogweed are flattened and
oval in shape. This plant produces a clear, toxic watery sap that causes a skin
reaction known as photodermatitis.

2. Where is found?
Roadsides, stream banks, waste areas and other scattered locations.

3. What information does the Agency have?
 The agency has an information note on giant hogweed (see attached).

4. Why is it noxious?
Its watery, clear sap contains photosensitizing compounds, which, when in contact with the skin and in combination with UV radiation, can cause dermatitis in sensitive individuals. The symptoms may range from skin inflammation to serious blisters and scars.

5. How do you treat exposure?
First prevent exposure by wearing gloves, protective clothing and protective eyewear when working with the plant(s). Cutaneous surfaces exposed to sap should be washed extensively with water. Further exposure of the affected skin to UV/Sunlight should be avoided. If photo dermatitis occurs, medical consultation should be sought.

If there has been direct exposure to the eye (cornea), flushing the eye with water is immediately required and the individual should seek medical evaluation and treatment on an urgent basis.

6. What is the ministry’s response?
The Ministry of Natural Resources is the lead on Giant Hogweed. At the local level, the handling of noxious weeds is a shared responsibility with the municipality in which the weed is found. The Public Health Unit would assist in the provision of material for raising awareness about this potential health hazard, precautions and advice if exposed. Health services should be aware of the issue in order to appropriately treat it.

7. What is the role of the Public Health Unit?
The role of the Public health Unit is to assist in the provision of material concerning the health threat, precautions and advice if exposed. The local level also works closely with regional Ministry of Natural Resources offices and several public health units have links to MNR on their websites.

8. Where can you find additional information on giant hogweed?
Additional information on Hogweed you may be obtained by calling the Invading Species Hotline at 1-800-563-7711 and from the following websites:

http://www.invadingspecies.com
http://www.ontarioinvasiveplants.ca/files/LandownerGuideInvasives_web.pdf
http://www.omafra.gov.on.ca/english/crops/facts/ontweeds/giant_hogweed.htm
http://www.omafra.gov.on.ca/english/crops/insects/weeds.html
http://www.ontarioweeds.com/weed.php?w=HERMZ
http://www.invadingspecies.com/Invaders.cfm?A=Page&PID=31

http://www.nerc-wallingford.ac.uk/research/capm/pdf%20files/4%20Giant%20Hogweed.pdf