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Giant Hogweed: A Menace To People And Wildlife

Posted: Wednesday 19th July 2017 by RiverSearch

Tom Richards - Wye and Usk Foundation

Growing to a height of 3.5m, Giant Hogweed dwarfs most other invasive plant species and can cover whole fields once established. It is particularly dangerous to people, with children being the most vulnerable.

Although an impressive sight when fully grown, giant hogweed (Heracleum mantegazzium), is invasive and potentially harmful. Chemicals in the sap can cause photodermatitis or photosensitivity, where the skin becomes very sensitive to sunlight and may suffer blistering, pigmentation and long-lasting scars

There is also a native hogweed, Heracleum sphondylium, which is a familiar sight around the countryside. It can grow to six foot or so when in flower but is nevertheless a much smaller plant than giant hogweed. It can cause rashes and other skin complaints but reactions tend not be as severe as with the larger species.

The giant hogweeds were introduced into Britain and Europe from the Caucasus Mountains in the nineteenth century as a Victorian garden plant.
Unfortunately they quickly escaped from cultivation with the first naturalised (‘wild’) population recorded in Cambridgeshire in 1828, and are now widely naturalised as invasive species throughout much of Britain and Europe.

The flowers are white and held in umbels, (flat-topped clusters, like those of carrots or cow parsley), with all the flowers in the umbel facing upwards. The flower heads can be as large as 60cm (2ft) across. It can reach a height of 3.5m (11.5ft) or more and has a spread of about 1-2m (3.5-7ft).

Giant hogweed is usually biennial, forming a rosette of jagged, lobed leaves in the first year before sending up a flower spike in the second year and then setting seed.

Giant Hogweed has been recorded in Surrey by RiverSearch volunteers mainly on the headwaters of the river Arun close to Haslemere. It is now also starting to move along the South Wey towards Liphook.
The plant is best tackled by trained operatives who will inject the stem with a herbicide.

If you come across this plant, keep a good distance away and don’t allow children or dogs near. You can send in details of your sightings to

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