Giant Hogweed
(Heracleum mantegazzianum) Description and Variation: 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. Economic Importance: Giant hogweed has been introduced to Europe, the United Kingdom, Canada, and the United States as a garden curiosity. Because of its tenacious and invasive nature it soon becomes a pest within the ornamental garden and readily escapes. It has naturalized in many of the places where it was first introduced. Growing along streams in Ontario, on Vancouver Island, and in Great Britain it forms a dense canopy outcompeting native riparian species and results in an increase in soil erosion along the stream banks where it occurs. The plant exudes a clear watery sap which sensitizes the skin to ultraviolet radiation. This can result in severe burns to the affected areas resulting in severe blistering and painful dermatitis. These blisters can develop into purplish or blackened scars. Proliferating populations in urban and suburban areas represents an increasing public health hazard. Giant hogweed is currently on the federal noxious weed list. It is listed as a Class A weed on the Washington State Noxious Weed List. Its placement on these lists were due to its potential menace as a public health hazard. The number and size of populations in the Seattle area, where it has been observed over the past four years, continue to grow annually. Literature reviewed indicates it naturalizes readily once it escapes from ornamental gardens where it is often cultivated as a garden curiosity. Populations throughout Europe, the United Kingdom, Ontario, Vancouver Island, and in New York State are all thought to have gotten their start in this manner. Once established it crowds out other native plant species and increases soil erosion along stream banks. Giant hogweed is a tenacious perennial which is difficult to eradicate. Targeting all known populations for control will prevent the further spread of giant hogweed in Washington. Geographic Distribution: Habitat: Giant hogweed may colonize a wide variety of habitats but is most common along roadsides, other rights-of-way, vacant lots, streams, and rivers. Because giant hogweed often grows in wet areas, we are considering it to be an invasive freshwater weed. HistoryHistory: Personal communication between J.K. Morton and C. Leo Hitchcock indicates Hitchcock knew of at least one population in the Seattle area during the early 1950's. This would be the earliest documented record of this species in Washington. Growth, Development, and Reproduction: Giant hogweed is a perennial which takes several years from germination to produce the first flowering stalk. It is believed to be monocarpic, dying after first flowering and seed set. Individual plants however, may produce additional crowns which continue to flower and set seed. Seed longevity is known to be greater than seven years. Reproduction is through seed and perennating buds formed on the crown and tuberous root stalk. Abundant seed production, a persistent root stalk, and vegetative reproduction from perennating buds are cited as reasons for its capability to colonize rapidly and expand populations. Response to Herbicides: 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). Response to Cultural Methods: 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. Biocontrol Potential: 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. Notes: Giant hogweed, Heracleum mantegazzianum, is on the federal noxious weed list. Introduction through imports into the United States is illegal; interstate and intrastate movement of this species is illegal. Russel Hahn, Weed Scientist, Cornell University, 3-7-90, 607-255-1759, (personal communication) noted giant hogweed is an escaped ornamental in New York state where it is found along roadsides and in vacant lots. The spread of this plant appears to be slow but steady. Concern in New York centers around the ability of this plant to cause photodermatitis in people. Children are particularly prone because of its occurrence in vacant lots and its use as a make-shift weapon. References Andrews, A. H., Giles, C. J., and L. R. Thomsett. 1985. Suspected poisoning of a goat by giant hogweed. Veterinary Records. February 1985. 116(8):205-207. Arora, K., Grace, J. and F. Stewart. 1982. Epidermal features of Heracleum mantegazzianum Somm. & Lev., Heracleum sphondylium L. and their hybrid -- scanning electron and light microscopy, taxa discrimination. Botanical Journal of the Linnean Society. October 1982. 85(3):169-177. Barclay, G. F., Oparka, K. J., and R. P. C. Johnson. 1977. Induced disruption of sieve element plastids in Heracleum mantegazzianum. Journal of Experimental Botany. 28(104):709-717. Barclay, G. F. 1982. Slime plugs do not inhibit surge flow in sieve tubes Heracleum mantegazzianum L., Heracleum sphondylium. Plant Physiology. 60(7):1281-1284. Bechtle, W. 1977. Beware of Hercules (Heracleum mantegazzianum]. Kosmos. 7:502-506. Clegg, L. M., Grace, J. 1974. The distribution of Heracleum mantegazzianum (Somm. & Levier) near Edinburgh. Transactions from the Proceedings of the Botanical Society of Edinburgh. 42(2):223-229. Davies, D.H.K. and Richards, M.C. 1985. Evaluation of herbicides for control of giant hogweed (Heracleum mantegazzianum Somm & Lev.), and vegetation re-growth in treated areas. Tests of Agrochemicals and Cultivars. Annals of Applied Biology. April 1985. (6) p. 100-101.* Dawe, N.K., White, E. R. 1979. Giant Cow Parsnip (Heracleum mantegazzianum) on Vancouver Island, British Columbia. Canadian Field Naturalist. 93:82-83.* Dreher, K. 1972. On yield improvement: giant cow parsnip. [Heracleum mantegazzianum, honey plants]. Biene. 108(10):307-308. Ezeala, D. O., Hart, J. W., and D. D. Sabnis. 1974. Fractionation of monovalent ion-stimulated nucleoside triphosphatase activity in extracts of petiolar tissues [Heracleum mantegazzianum, sunflowers]. Journal of Experimental Botany. 25(89):1037-1044. Ezeala, D. O., Hart, J. W., and D. D. Sabnis. 1974. Stimulation by monovalent cations of adensosine triphosphatase activity in extracts of petiole tissues [Heracleum mantegazzianum, sunflowers]. Journal of Experimental Botany. 25(89):1045-1052. Fischer, F. C., Jasperse, P. H., Karlesen, J., and A. Berheim-Svendsen. 1974. A new furancocumaringlycoside from Heracleum mantegazzianum. Phytochemistry. 13(10):2334-2335. Fischer, F. C., van Doorne, H., Dannenberg, G. 1982. Glycosides and glycosidase in Heracleum mantegazzianum their possible role in resistance against fungi. Monographs in Systematic Botany of the Missouri Botanical Garden. The Garden. 6:783-792. Grace, J., Stewart, F. 1982. Hybridization in the genus Heracleum in the British Isles Heracleum sphondylium with Heracleum mantegazzianum, ecosystems. Monographs of Systematic Botany of the Missouri Botanical Garden. The Garden. 6:773-782. Hart, J. W., Sabnis, D. D. 1973. Colchicine binding protein from phloem and xylem of a higher plan. Planta. 109(2):147-152. Hart, J. W., Sabnis, D. D. 1976. Binding of colchicine and lumicolchicine to components in plant extracts [Heracleum mantegazzianum]. Phytochemistry. 15(12):1897-1901. Hart, J. W., Sabnis, D. D. 1975. The occurrence and some properties of a new filamentous component of plant extracts [Heracleum mantegazzianum, electronmicroscapy]. Annals of Botany. 39(159):153-159. "Horticulture: The Magazine of American Gardening". November 1991* Hypio, Peter, Cope, Edward. 1982. Giant Hogweed, Heracleum mantegazzianum. Cornell Cooperative Extension. Misc. Bulletin 123.* Kees, H., Krumrey, G. 1983. Heracleum mantegazzianum -- ornamental plant, weed and poisonous plant. [toxicity to livestock and humans, control]. Gesunde Pflanzen. Kommentator. April 1983. 35(4):108-110. Morton, J. K. 1975. The giant cow parsnip, Heracleum mantegazzianum Umbelliferae, in Canada. Candian Field Naturalist. 89(2):183-184.* Morton, J.K. 1978. Distribution of giant cow parsnip (Heracleum mantegazzianum) in Canada. Canadian Field Naturalist. 92(2):182-185.* Murphy, R. 1986. A reanalysis of particle motion in sieve tubes of Heracleum. Annals of Botany. May 1986. 57(5):667-674. O'Brien, T. P., McCully, M. E. 1970. Cytoplasmic fibres associated with streaming and saltatory-particle movement in Heracleum mantegazzianum. Planta. 94(1):91-94. Rubow. T. 1979. Control of Heracleum mantegazzianum in economic crops. Medd-Statens-Planteavlsforsog. 81(1497):4p. (in Danish) Sabnis, D. D., Hart, J. W. 1974. Studies on the possible occurrence of actomyosin-like proteins in phloem. [Heracleum mantagazzianum]. Planta. 118(4):271-281. Stewart, F., Grace, J. 1984. An experimental study of hybridization between Heracleum mantegazzianum Somm & Levier and Heracleum sphondyllium L. subsp. sphondylium (Umbelliferae) [Transfers of pollen between the parent species]. Watsonia. August 1984. 15(2):73-78. Vanhaelen, M. Vanhaelen-Fastre, R. 1974. Furanocoumarins from the root of Heracleum mantegazzianum. Phytochemistry 13(1):306. Vanhaelen-Fastre, R., Vanhaelen, M. 1973. Polyacetylenes in C17 of Heracleum mantegazzianum roots. Phytochemistry. 12(11):2687-2689. Weimarck, G., Stewart, F., and J. Grace. 1979. Morphometric and chromatographic variation and male meiosis in the hybrid Heracleum mantegazzianum x Heracleum sphondylium (Apiacease) and its parents. Hereditas. 91(1):117-127. Wright, M. 1984. Giant hogweed: time for action is now [Heracleum mantegazzianum, Great Britain]. New Scientist. April 1984. 101(1404):44.* Yapa, P. A. J., Spanner, D. C. 1972. Isoelectric focusing of sieve-tube protein. Planta. 106(4)369-373. |
Giant hogweed is native to the Caucasus mountains
and southwestern Asia. It has been introduced to the European continent, the United
Kingdom, Ontario, Vancouver Island (Canada), and New York State as a garden ornamental.
From these initial sites of introduction it has escaped and naturalized. In Washington it
has been reported from Thurston, Kitsap, Mason, King, Island, and Clark counties. Escaped
populations in the Seattle area are known from Lake Washington Boulevard, West Seattle,
and the Wallingford area. Individuals have recently been noted along Interstate 5 in
Seattle and Rainier Avenue south near Renton.