James Rogers, Conservation Officer 
forestry@county.haliburton.on.ca

Forestry/Tree Harvesting Bylaw Enforcement

James Rogers, Conservation Officer
forestry@county.haliburton.on.ca

Forest Pests – Giant Hogweed, Heracleum mantegazzianum Somm. & Lev

Stems & Roots: Typically 10-15cm (4-6in) in diameter with coarse hairs, flowering stems up to 5m (16ft) high, hollow except at the nodes; both stems and petioles having conspicuous reddish-purple flecks throughout and sometimes completely purple near the base; lower stem often very rough with sharp-pointed, irregularly-spaced bumps.

Leaves: Leaf blades of rosette leaves very large, up to 1m (40in.) across. Compound leaves with 3 large deeply cut leaflets, each leaflet with deep irregular lobes and coarse, sharp teeth on all margins; their petioles (stalk that joins the leaf to the stem) often have sharp-pointed bumps similar to those on the flowering stems; leaves on the flowering stem are of similar shape but smaller, the upper ones often not divided but just deeply 3-lobed.

Flowers & Fruit: white or rarely pinkish in colour, appear in mid-june and are clustered in an umbel shaped head and can measure up to 120cm (4ft) across. Umbels are an umbrella shaped cluster of short-stalked flowers, typical of the carrot family. Each compound umbel consist of many (approximately 30 to 50) branches, each branch ending in a simple umbel with approximately 30 to 40 flowers

Caution: It has been implicated as a cause of severe dermatitis in a few susceptible individuals.

Further information on the Giant Hogweed can be found in the links below:
https://haliburtoncounty.ca/wp-content/uploads/2013/01/HogweedLookAlikes.pdf
Giant Hogweed (Fact Sheet)
OMNRFs factsheet
http://www.omafra.gov.on.ca/english/crops/facts/ontweeds/giant_hogweed.htm
http://www.ontarioinvasiveplants.ca/files/unwantedlettersGiantHogweedFINALPRESS.pdf
http://www.ontarioinvasiveplants.ca/index.php/managecontrol