Wednesday, August 06, 2008

Giant Hogweed Alert


Giant Hogweed (Heracleum mantegazzianum) is a member of the parsley or carrot family, Apiaceae (Umbelliferae). As its name indicates it is characterized by its size and may grow to 15 to 20 feet in height. Except for size, it closely resembles cow parsnip, Heracleum lanatum, a plant native to Washington. It is further distinguished by a stout dark reddish-purple stem and spotted leaf stalks. Stalks and stem produce sturdy pustulate bristles. The stem and stalks are hollow, stems vary 2 to 4 inches in diameter. The compound leaves of giant hogweed may expand to five feet in breadth. Each leaflet is deeply incised. Giant hogweed is a perennial with tuberous root stalks, which form perennating buds each year. The inflorescence is a broad flat-topped umbel composed of many small white florets. Each inflorescence may attain a diameter of 2-1/2 feet. The florets produce large elliptic dry fruits marked with brown swollen resin canals up to 1 mm in diameter.

Impact on humans and the environment: The greatest concern from Hogweed is human health. The blister-like pustules on stems and stalks exude a clear watery sap that sensitizes skin to ultraviolet radiation. Affected areas are subject to severe burns that usually result in blistering and painful dermatitis. Blisters often result in purplish to blackened scars. Hogweed’s tenacious and invasive nature allows it to readily occupy and crowd out native vegetation. In riparian areas, it forms a dense canopy, out-competing native species and causing stream bank erosion.
Management techniques: If Hogweed is growing in a park or on a public right-of-way, please call the City of Nanaimo at 755-7515. If Hogweed is growing on private property, please adhere to the following precautions:

Use protective clothing, gloves and face visor or similar to undertake any cutting or removal of this species.

Clear above ground leaf and stem material by hand; remove ground material of roots and seeds.

Bio-control: Cattle and pigs are cited as possible bio-control agents. Both eat Hogweed without apparent harm.


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