Giant hogweed contains furocoumarins, chemicals which can cause phytophotodermatitis (plant-light-skin inflammation), a severe reaction from exposure to the sun after coming into contact with the sap. This causes burns and blisters to appear two to three days after exposure. Contact with the eyes can cause temporary and possibly permanent blindness. Since the plant is huge, people are attracted by its novelty and, unaware of the danger, plant it and share starts with other gardeners. Children are attracted by its size and hollow stems which they pick for telescopes or pea shooters. Unlike poison ivy, just touching the surface of the plant can be harmless, although you can pick up sap from brushing the numerous hairs on parts of the stem.
Giant hogweed is native to the Caucasus region of Eurasia. Giant hogweed was first reported as established in Michigan in 1991, when it was found in a field in Ingham County (Case and Beaman 1992). Today there are approximately 30 known sites in the State, most in Gogebic County in the western Upper Peninsula. In 2005 the State of Michigan included giant hogweed on a list of prohibited plant species. The State designation makes it a violation of both federal and state law to move or plant giant hogweed. Counties in Michigan with a noxious weed program can also require treatment of infested property.
In some areas, Giant hogweed can invade natural habitats, while in other areas it appears to mostly persist where planted near homes. Giant hogweed may become established in rich, moist soils along roadside ditches, stream banks, waste ground, along tree lines, and open wooded areas.
Giant hogweed may be easily confused with the native cow parsnip.
See the more information links on left for photos and tips on how to tell them apart.
Some useful characters are given in the following table:
In Michigan, twenty sites are known within Gogebic County, including fifteen sites within the City of Ironwood. Another four sites are known to occur in neighboring Iron County, Wisconsin, the first known sites in that State. Most of the sites are in yards around homes. From speaking with owners, the plant appears to have been a popular garden curiosity thirty to fifty years ago, when plants were shared among friends. Several new sites were found when elderly homeowners remembered where they obtained their hogweed, and who they gave it to. Hogweed may also have been planted for its seeds, which are used in Middle Eastern cooking.
After purchasing a home in Ironwood in 2002, Craig Poorker found over one hundred giant hogweed plants growing along the edge of his backyard. Not aware of the plant’s identity or health risk, he used a machete to cut the plants down on a sunny summer day, wearing shorts. He suffered severe skin reactions on his legs (click to see photo and also below) and required two visits to the emergency room where staff tried to identify and treat the mysterious rash. (Also see MDA brochure.)
In 2005 the City of Ironwood formed a giant hogweed partnership with Gogebic County Extension, Wisconsin Department of Natural Resources, Michigan Department of Agriculture, Gogebic Conservation District, Iron County Extension (WI), the US Forest Service, and the Michigan Invasive Plant Council. The partners created a Giant Hogweed Cooperative Weed Management Area covering Gogebic County, Michigan, and Iron County, Wisconsin. In 2005, with the help of the partner groups, the City of Ironwood received a $24,000 grant from the National Fish and Wildlife Foundation, Pulling Together Initiative. The funds were used to hire a professional herbicide applicator (4 Control) to spray giant hogweed infestations, where the landowners were unable or unwilling to treat the plants themselves. Click here for a copy of the project application and here for the Memorandum of Understanding.
Before and after treatment photos
4 Control treated approximately twenty giant hogweed infestations in 2006 and 2007. They primarily used a foliar spray of 5% triclopyr (Garlon 3A) and 2% clopyralid (Transline). This mixture was recommended by the Pennsylvania Department of Agriculture, where giant hogweed has invaded many natural areas. Since then, the Transline label has changed and use of that herbicide in ornamental areas around homes is no longer permitted. Triclopyr, however, is a common herbicide active ingredient available from most hardware and home and garden stores. 4 Control also tested two other herbicides on giant hogweed: metsulfuron methyl (Escort) and aminopyralid (Milestone), and both worked well.
Mechanical treatment methods may also be used, such as repeated mowing or root cutting (about 4 inches below the ground). These methods pose a risk for sap contact. If you plan to treat an infestation with any method, be sure to wear appropriate skin protection such as long sleeves, long pants, gloves and eye protection. If you attempt to kill giant hogweed plants already in bloom, avoid spreading seeds by bagging the flower and seed umbels. If you think you may have giant hogweed on your property, or have seen an infestation elsewhere, please contact the Michigan Department of Agriculture.
Treating a giant hogweed burn
Treatment of burns from giant hogweed may require a visit to a physician. Some medical information on treatment of phytophotodermatitis is available here. The Wisconsin Department of Natural Resources has offered guidance for treating burns for wild parsnip. Wild parsnip also causes photodermatitis, and is a relative of giant hogweed, both in the carrot family (Umbelliferae). The wild parsnip burn recommendations are available here. Other plants in the carrot family can also cause the skin reaction, although generally less intensively than giant hogweed. These plants include wild parsnip, cow parsnip, Queen Anne’s lace (wild carrot) and celery.
Giant hogweed (Heracleum mantegazzianum) is a federally-listed noxious weed in the Carrot Family, known for its enormous size and ability to cause severe skin reactions. The size of giant hogweed makes it an ornamental curiosity. Flowering stems can reach heights of eight to fourteen feet, and the leaves can be up to five feet across. As a federal noxious weed, it is illegal to bring giant hogweed into the United States or to move it across state lines. It is also illegal to sell, buy, exchange or give these plants and plants may be seized or treated and infested areas quarantined.