Giant Hogweed is a public health hazard that ranks up there higher that poison ivy, poison oak and poison sumac in respect to its potential to harm humans. The reason for concern is that the sap from this plant can cause a severe skin reaction known as photo-dermatitis or photo-sensitivity. The reaction can happen up to 48 hours after contact. After coming in contact with the sap, the skin blisters when exposed to sunlight. Contact with the eyes can lead to temporary or possibly permanent blindness. The weed can be especially troublesome for children that may find the long stems attractive to play with. There are accounts from Great Britain about instances where children suffered from severe skin reactions after playing with the hollow stems as pea-shooters, telescopes and even play swords. If you do come into contact with the plant, and especially the sap, you are advised to wash the affected areas immediately, keep the exposed area out of direct sunlight and seek medical advice.
Besides these public health concerns, Giant Hogweed is also reported to be invasive under certain conditions. It does especially well in disturbed soils and also along waterways where seeds can be spread long distances. Large colonies have been known to form from a single plant, where an abundance of seeds coupled with shoots arising from the roots gives rises to dozens of offspring. Weed specialists have reported that once it becomes established it takes up to five years to completely get rid of a colony due to regrowth from seeds and roots.
This unwanted plant is found on the Federal Noxious weed list. This means that it is illegal to sell or transport it across state lines, a violation punishable by fines. Florida, North Carolina, Oregon and Washington also regulate giant hogweed as a noxious weed.
Giant Hogweed was introduced into North America in the early 1900s. Its native range is Central Asia, although now it now occurs throughout the United Kingdom, Australia, Europe, parts of Canada and the United States. It is suspected to have made its way into this country as an ornamental. Its size made it somewhat of an oddity and gardeners that wanted something unique imported it.
Giant Hogweed has been confirmed in 11 counties in Michigan: Branch, Calhoun, Gogebic, Ingham, Jackson, Kalamazoo, Kent, Manistee, Oakland, Ottawa and Saginaw. The rest of Michigan should be watchful for this species. It's reported distribution in North America includes Maine, Michigan, New York, Pennsylvania and Washington in the U.S. and in the Canadian provinces of British Colombia and Ontario. Small colonies of giant hogweed have recently been found in Indiana, Maryland, Ohio and Vermont where eradication is underway.
Giant Hogweed (Heracleum mantegazzianum) is a member of the carrot or parsley family. Plants that are similar in appearance in that same family are cow parsnip and angelica with Queen Anne's lace as a distant third choice. The plant most often mistaken for Giant Hogweed is cow parsnip due to the similar appearance and the fact that cow parsnip is widespread in Michigan. One distinguishing feature that separates Giant Hogweed from these other plants is its size: 15-20 feet tall. In comparison, cow parsnip only reaches a modest height of 3-4 feet. Other unique features include its stout, dark reddish-purple stem and spotted leaf stalks. The flowers appear in typical white umbrella-like clusters. The stems may be 2-4 inches in diameter while the leaves may be up to 5 feet across. Colonies of Giant Hogweed are evident in the winter months by the massive stalks poking up through the snow, even in the worst of our winters.
If you have seen a plant that appears to be Giant Hogweed, report it to the Giant Hogweed Hotline at 800-292-3939 so that it can be examined by professional staff of the Michigan Department of Agriculture.
Check out the MDA/USDA brochure on Giant Hogweed.
A few informative web sites are:
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