Description:
Giant hogweed is a member of the parsley or carrot family, Apiaceae (Umbelliferae). As its name indicates, it is characterized by its size and may grow 15 to 20 feet tall. Except for size, it closely resembles cow parsnip, Heracleum lanatum, a plant native to Washington. It is further distinguished by a stout, dark reddish-purple stem and spotted leaf stalks. Stalks and stems produce sturdy pustulate bristles. The stem and stalks are hollow. Stems vary from two to four inches in diameter. The compound leaves of giant hogweed may expand to five feet in breadth. Each leaflet is deeply incised. Giant hogweed is a perennial with tuberous root stalks which form perennating buds each year. The inflorescence is a broad flat-topped umbel composed of many small white florets. Each inflorescence may attain a diameter of two and a half feet. The florets produce large elliptic dry fruits marked with brown swollen resin canals up to one mm in diameter.

• Mechanical: Plants may be dug-out, but care should be taken to remove much of the root stalk. This can be difficult and unpleasant. Always wear protective clothing and avoid getting the sap on your skin. Mowing serves only to stimulate budding on the perennating root stalk, but might be successful if done consistently and persistently enough to starve the rootstalk
• Biological: Cattle and pigs are cited as possible biocontrol agents. Both eat giant hogweed without apparent harm. Trampling also damages the plant. Whether any formal investigation for phytophagous insects in giant hogweed's native range has been conducted is unknown.
• Herbicide: 2,4-D, TBA, MCPA and dicamba will kill above ground parts but are reportedly not particularly effective on persistent rootstalks. Glyphosate is considered the most effective herbicide and should be used cautiously around desirable species since it is nonselective. Application during bud stage and while the plant is actively growing is recommended by New York Cooperative Extension. In Great Britain, Wright recommends application during the early growing stages (late March to early April). In wet areas, Rodeo® (glyphosate)is the only herbicide permitted for use in Washington. Refer to the State Noxious Weed Control Board site

For More Information:
Detailed information about Giant Hogweed is available at the Washington State Noxious Weed Control Board Web Site.