Giant Hogweed................be cautious

Giant Hogweed – General Information

What Is Giant Hogweed?

Giant Hogweed (Heracleum mantegazzianum) is a perennial member of the parsley or carrot family originally native to Asia but now found naturally in South Central Ontario. It closely resembles cow parsnip and Queen Anne’s Lace except, as its name suggests, it is characterized by its large size and may grow as high as 6 meters. Aside from its immense size, Giant Hogweed can also be distinguished by its stout, dark reddish stem that can grow 5-10 cm in diameter. Leaf stalks are spotted and can produce a leaf that can expand to 1.5 meters across (see picture below). Each leaf is deeply grooved or divided. Stems and stalks are hollow and produce course hairs around a blister like area on the plant. In summer, small, white flowers form together to make up an umbrella-shaped head that can reach 1 meter in diameter.

Where is Giant Hogweed Found ?

Giant Hogweed can be found in scattered localities across Southern Ontario however, isolated plants have been documented as far north as Haliburton County. Although it may grow in a wide variety of habitats, it is most often found along roadsides, other right of ways, vacant lots, wet areas (stream and river banks) and waste areas.

Why be concerned about Giant Hogweed?

The blister like areas on stems and stalks leak a clear watery sap containing chemicals classified as psoralens, which can sensitize the skin to ultraviolet radiation. Exposure to sunlight following contact with these chemicals causes severe burns that usually result in blistering and painful dermatitis. Blisters can develop into purplish or blackened scars sometimes up to 48 hours after exposure. In some cases, skin contact can lead to recurring dermatitis and eye contact can lead to temporary or possibly permanent blindness.

Who is at increased risk of exposure?

Employees working outdoors in areas such as roadsides, other right of ways, near streams or river banks are potentially at risk of exposure to this plant.

How can I protect myself?

· Review the above pictures so that you are aware of what the plant looks like.
· Avoid contact with the plant.
· Wear a long sleeved shirt and long pants to avoid skin contact.


What should I do if I come in contact with this plant?

· Wash the affected area with soap and water.
· Keep affected areas out of direct sunlight.
· Seek medical advice at the earliest opportunity.