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Watch out for Giant Hogweed

Sudbury Living Magazine June 1, 2012 Home & Garden No Comments on Watch out for Giant Hogweed

Giant Hogweed

Giant Hogweed (Heracleum mantegazzianum) is an invasive species introduced to North America in the early 1900’s as an ornamental garden plant. It is now widespread in the northern US and southern Canada with increasing reports within Ontario since its first confirmed record in 1949. Linda Hugli, Director of Master Gardeners of Ontario and VP of the Sudbury Horticultural Society, says it is an “unwelcome guest which has begun to make itself quite comfortable in and around the Greater Sudbury area.”

Invasive or “aggressive” species can quickly turn into ecological disasters as they displace native species and disrupt local food webs. Examples of introduced invasive species that have resulted in changes in local flora are Eurasion water milfoil and purple loosestrife. Garden species that are invasive but may be unwanted are ground ivy and crown vetch. Giant hogweed has a characteristic that makes it stand out from the rest – its toxic or caustic sap.

Why is it dangerous?

The sap contains a chemical compound which causes phytophotodermatitis in susceptible people, causing their skin to become super-sensitive to the sun’s ultraviolet rays. Initially the skin colours red and starts itching – then serious skin burns and blisters form within 48 hours. The resulting purplish scars can persist for several years. In addition, the presence of tiny amounts of sap in the eyes can lead to temporary blindness.

What does it look like?

Giant Hogweed is a perennial of the parsley family and is identifiable by its height, which usually ranges from 3-20 feet (1-5.5 metres)! It usually does not have flowers until it is over 2 metres tall, has thick hollow stems and large deeply lobed leaves.

Height : 1-5.5 metres (3’-20’) !
Stems: hollow, ridged 4-10 cm in diameter at the base with dark reddish-purple splotches and coarse white hair.
Leaves: Large with three deeply cut leaflets, irregular lobes and coarse, sharp teeth on all margins.
Flower: white, compound umbel (width of 8+cm) made up of 4-12 smaller flat round units.

Will the city remove the Giant Hogweed from my property?
No. It is residents’ responsibility to remove plants found on their property. The city will remove those plants found on or near municipal facilities. Residents should not remove or dispose of a Giant Hogweed plant without professional help or advice.

What do I do if I have spotted Giant Hogweed?

Various programs are in place to track the distribution and movement of Giant Hogweed or other invasive species. You may call the Invading Species Hotline at 1-800-563-7711, or visit The Ontario Ministry of Natural Resources is also mapping Giant Hogweed populations and you can report online at

Within the City of Greater Sudbury, phone 311 to report Giant Hogweed sightings.

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