Most (un)wanted plant of the month:
Giant Hogweed
Heracleum mantegazzianum
Description:
A member of the parsley and carrot family, giant hogweed can be distinguished from most other plants in that family by its massive size. It is a perennial herbaceous plant with enormous, dark green leaves and hollow stems with purple blotches that can reach a height of 2.5 to 5 metres when in flower. The flowers are borne in large umbrella-shaped clusters which can be up to 0.8m across. The seeds are winged and oval and approximately 1cm long. Each giant hogweed plant can produce up to 50,000 seeds. Giant hogweed produces toxic compounds which, when human skin comes into contact with it, can cause \"phyto-photodermatitis\". This makes the skin extremely sensitive to sunlight resulting in painful blistering and scarring of the skin, akin to third degree burns.
Ecology:
Giant hogweed grows best in rich, moist soils in both open and partially-shaded areas. It will take from 3 to 8 years before it produces seed, depending on how good the growing conditions are.
What makes it invasive?
Giant hogweed produces copious seeds, grows from a dense taproot which keeps producing leaves and is also very dangerous to human health, making it difficult to remove. In the UK, giant hogweed is considered toxic waste.
How to control it:
Control must be conducted very carefully so as not to touch the leaves and get the sap on your skin. Waterproof clothing including gloves, boots and safety goggles should be used. The best way to rid an area of a hog weed infestation is to excavate the plants with the soil, and to bury the waste under at least 2 metres of soil. As this may not be an option for most individuals, another option is to repeatedly remove all vegetation, cut the root crown at an angle (below the soil surface) with a sharp spade, and mulch the area with deep soil or bark, planting with shrubs. Remember to use extreme caution when handling giant hogweed. If the plants have already gone to seed, it is possible to simply cut the seed heads and bag them for disposal, then cut the remaining vegetation and leave on-site to decompose. It will be necessary to return to the site repeatedly over the next couple of years to maintain a hogweed-free site.
Additional Information:
BC distribution, detailed species information and additional photos available here.
Ecology and Management of Giant Hogweed (Heracleum mantegazzianum), edited by P. Pysek, Institute of Botany Prhonice, Czech Republic; M. J. W. Cock, CABI, Switzerland; W. Nentwig, University of Bern, Switzerland and H. P. Ravn, Forest & Landscape, Denmark. January 2007, 352 pages. Available here from Amazon for $84.
The Giant Hogweed: Best Practice Manual available here. The manual provides up-to-date knowledge about all relevant aspects of the biology, ecology, taxonomy and management of invasive hogweeds. It is very useful and accessible to a broad audience.
King County Noxious Weeds Giant Hogweed website includes photos, identification information, and links to best management practices for control, and a online form for reporting occurrences.
The Biology of Invasive Alien Plants in Canada, Giant Hogweed (Heracleum mantegazzianum). N. A. Page, R.E. Wall, S. J. Darbyshire, and G. A. Mulligan, 2006. Review paper in the Canadian Journal of Plant Science, 86. Available at http://www.raincoastappliedecology.ca/plantecology.html.
Petr Pysek (Czech Invasion Ecologist) website available here. Dr. Pysek has undertaken a number of studies on giant hogweed.
Biological flora of the British Isles, Heracleum mantegazzianum Sommier & Levier. Tiley, G. E. D., S. D. Felicite, and P. M. Wade, 1996. Journal of Ecology 84: 297-319. Review paper with emphasis on British and European populations. Not available online (see UBC Library for hard-copy).
date posted: 19/10/2007
LIST OF MOST (UN)WANTED PLANTS:
Giant Hogweed Heracleum mantegazzianum |
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