Fact Sheet

Giant Hogweed is a serious invasive plant that poses a moderate threat to human health and safety. The plant is native to Europe and Asia and was introduced as an ornamental. It is found in many areas in southern Ontario, and has recently been discovered in Renfrew County and small populations of the plant have been confirmed in the City of Ottawa. In each case municipal staff has started localized removal of the plant.

Description

Giant Hogweed is a long-lived perennial plant. It can take 3 to 4 years before flowering and flowers only once in its life. It can range in height from 1 to 5.5 metres. Plants produce huge leaves that are up to 1 metre in width. Leaves are deeply cut, with large lobes, and sharp teeth on all leaf margins.

It has sharp pointed bumps on stems and leaf petioles. Stems have reddish purple flecks and are often entirely purple at the base. Stems are mostly hollow and up to 10 cm in diameter. Stems and petioles are densely hairy.

Giant Hogweed flowers from June to August with white (sometimes pinkish) flowers in large clusters.

Pictures at the following link:

http://www.omafra.gov.on.ca/english/crops/facts/ontweeds/giant_hogweed.htm

Distribution and Habitat

Primarily found along roadsides, stream banks and disturbed open areas. Plants reproduce well on disturbed sites, and prefer full sun and open habitat common along roadsides and ditches in rural areas.

Ecological Impact

Can shade out and outcompete native vegetation, which is a concern in riparian areas along stream banks and natural areas.

Human Health Concerns

This plant is poisonous. Hollow stem, leaves and plant hairs produce a sap if broken. Sap can cause serious skin inflammation on contact. If contaminated skin is exposed to

sunlight a more serious reaction can occur including blisters, discolouration, and scars. If sap has contact with eyes, loss of vision, blindness or damage to eyes can occur.

Giant hogweed contact with bare skin should be avoided – this includes all portions of the plant.

If contact with skin occurs, avoid exposure to sunlight and wash the site immediately.
 
If a skin reaction occurs, seek medical attention.

Those working to control this plant should use goggles and waterproof gloves.
Long sleeves, pants and boots should be worn; Synthetic materials work best since most fabric will absorb plant sap or can be penetrated by the plant.

Clothing that comes in contact with plants should be washed.

Equipment used to control the plant should be washed with water immediately.

Management and Control

Giant hogweed is mainly spread by soil movement and contaminated equipment but can still be found in private gardens. Minimizing soil movement and regular equipment washing can help prevent new introductions.

This plant takes several years to reach its full size and to reproduce.  It is easy to see and identify due to its habitat and large size. For this reason local control efforts can be successful. Seed heads should be removed, bagged, isolated and allowed to heat for several days. Composting through a regular municipal compost program should ensure enough heat to destroy seeds. The remaining plant should be sprayed with a localized spray containing glyphosate (A common over the counter spray is ‘Round-up’ and can be found in various formulations).

This plant should not be removed with a brush saw or weed-eater.

Reporting

Suspected findings of Giant Hogweed should be confirmed through contacting the City of Ottawa at 3-1-1or through contacting the Natural Resource Information Centre at 1-800-667-1940 or by visiting www.ontarioweeds.com .