Originally from Asia, introduced as an ornamental in the early 1900s. Giant Hogweed is a biennial or perennial herb. Similar in appearance to cow parsnip but larger and with shorter hairs(.25mm) on the underside of the leaf. Giant Hogweed is in the carrot or parsley family and grows up to 15 feet tall when flowering. Its hollow stems are two to four inches in diameter. The stems have dark red-purple spots and coarse white bristles. The leaves are deeply incised and compound and can be up to five feet in width. It flowers in mid-May through July. The flowers are white and clustered in an umbrella shape that may be up to two and a half feet in diameter. The fruits are 3/8-inch long, tan, flattened ovals with a broadly rounded base and broad marginal ridges.
The seeds can remain dormant in the soil for at least five years and can be spread to new areas by wind or water. The most common method of transportation to new areas is by people who transport seeds or young plants and sometimes use the dried fruit in decorations. Giant Hogweed prefers moist soil and thus is often found in roadside ditches, stream banks, and along treelines. It crowds out native species and produces toxic sap.
This plant is a public health hazard as it the sap can cause painful, burning blisters 24 to 48 hours after contact with skin. It can also cause blotches that develop into purple-brown scars that can persist for years. These blisters and scars occur when skin that has contacted the sap becomes moist and is then exposed to sunlight. This is known as phytophotodermatitis.
If you need to touch Giant Hogweed use disposable rubber gloves, wear a longsleeved shirt and pants. If you contact the sap, wash the area and avoid sunlight. Call a doctor for severe reactions. Wash any clothes that contact the sap.
In the United States it has been found in Pennsylvania, Maryland, Connecticut, DC, Maine, Massachusetts, Michigan, New York, Ohio, Oregon, Washington and Wisconsin.
To manage Giant Hogweed please contact the USDA, a professional plant control specialist or your Department of Agriculture. Mowing and cutting are ineffective means of removal due to Giant Hogweed’s large perennial root, which allows it to send up new growth.
Giant Hogweed Hotline: 1-800-292-3939
And this video: http://www.youtube.com/watch?v=KaV2jwNT0MQ discusses the problems with Giant Hogweed, I found it on http://www.invasivespeciesinfo.gov/
(From: http://www.michigan.gov/documents/MDA_Hogweed_Brochure_2_115074_7.pdf and http://www.kingcounty.gov/environment/animalsandplants/noxious-weeds/weed-identification/giant-hogweed.aspx and http://www.health.state.ny.us/environmental/outdoors/hogweed/giant_hogweed.htm)
