Large, toxic weed spreading across Canada

A toxic plant is spreading steadily across Canada. Giant hogweed (Heracleum mantegazzianum), which can cause long-lasting skin damage, is now found in many parts of North America, and is cropping up in Nova Scotia particularly.

The plant is tall (up to five metres when in bloom) with large, dark green leaves; small flowers which are usually greenish-white (sometimes purple) and grow in umbrellets; and a thick, speckled, hairy stem. The Invasive Plant Watch Network warns that the stem hairs, nodules and leaves contain a sap that is highly poisonous. About 15 minutes after contact with the plant a reaction is triggered by ultraviolet radiation. This can include burning and blisters, with the worst symptoms showing up between 30 minutes to two hours after contact. Skin may swell and be red about 24 hours after touching the plant, and seeping blisters may appear in three days. The Network said that some people suffer second degree burns, and in extreme cases they may remain sensitive to sun for as long as six years. If the sap gets into the eyes it can cause temporary blindness. According to the Invasive Plant Watch Network, giant hogweed, which is originally from the Caucasus Mountains in Southwest Asia, was purposely taken to Europe and North America as a curiosity. Being a plant that spread easily, it quickly escaped containment. It appeared in the wild in England in 1828, in the U.S. in 1917, and in Canada in the 1940s. It has also spread to Australia and New Zealand. In Canada, it has been identified in British Columbia, Ontario, Quebec, Nova Scotia, New Brunswick and Newfoundland. Not only is giant hogweed a danger to humans, it is also a threat to native plants. Each plant produces about 40,000 winged seeds which can survive in the ground for as long as 15 years. The plants grow in a wide variety of environments including urban areas, forests, wetlands, roadsides, and fields. Marian Munro, curator of botany at the Nova Scotia Museum, told CBC that people should not touch any part of the plant with their bare hands, and they should hire a professional to have it removed if it is growing on their property. Giant hogweed can grow again if cut, but may be controlled by mechanical cutting and uprooting, and by some herbicides. Giant hogweed is sometimes confused with cow parsnip, which is a smaller plant native to Canada.