Saturday, July 24, 2010

Giant Hogweed

More on Giant Hogweed from OMAFRA...
Giant hogweed, Heracleum mantegazzianum (which has been documented in Ontario since 1949) is distinguished by its huge size, its very large, compound leaf blades, its tall, thick, hollow, often sharply roughened stems, and its large flat-topped compound inflorescence with white flowers and large, flat fruits with prominent dark-coloured oil tubes. Flowering inflorescences are often heavily infested by aphids. Please see the following webpage from for additional information:

Ministry staff is aware of the significance of giant hogweed from a human health and invasiveness perspective. OMAFRA is working with the University of Guelph and several municipalities across the province to identify best management practices for giant hogweed

Giant Hogweed identification videos are now located on the OMAFRA website home page as well as at the following links:


What do to if you suspect giant hogweed:

1. Have the suspected plant properly identified. (Over half of the submissions that OMAFRA receives is from clients claiming they have Giant Hogweed, and are not Giant Hogweed.)
* Proper identification can be obtained by submitting a photo via

2. Once confirmed, send the location of the sighting to:
* Invasive Species Tracking System that is coordinated in part by the Ministry of Natural Resources. It can be found at
* your local municipality to inform them of the sighting

3. Landowner’s can purchase glyphosate products (i.e. Roundup) to control weeds that are poisonous to the touch, such as poison ivy, wild parsnip and giant hogweed. Homeowner’s and municipalities that are concerned about Giant Hogweed and wish to manage the plant do not need a noxious weed designation to do so.

* Please note: Giant hogweed can be a serious health hazard for humans. Its watery, clear sap contains photosensitizing compounds (furanocoumarins), which, when in contact with human skin and in combination with UV radiation, can cause burning. Content varies depending on plant part, but contact should be avoided at all times.

If you have been exposed to this plant, if is often suggested that you wash affected area immediately, avoid direct exposure to sunlight and seek medical advice.

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