Giant Hogweed (Heracleum mantegazzianum) is a non-native, invasive species in the UK and, similar to other invasive species, it was introduced as an ornamental plant in the 19th Century for its large white flowers. Giant Hogweed can grow up to 5m in height and is identified by its size, purple spotted stem and sharply cut leaf shape. On the stem, small “hairs” are found and these are filled with a phototoxic sap which causes phytophotodermatitis when the affected area of skin is exposed to sunlight, resulting in severe skin irritation and blistering.
As Giant Hogweed is a non-native species it has no predators, its sheer size dominates ecosystems and overpowers native species and ruins biodiversity. Coupled with the health and safety risk associated with the sap of the plant and the ease with which it spreads, each flower head can produce 1500 seeds and when dispersed can remain dormant in the soil for years, it must be eradicated from affected areas. Dr Lindsey Stenhouse describes the dangers of Giant Hogweed when in public areas and covers the work required to eradicate the weed on BBC’s Landward programme.
How to identify Giant Hogweed in Autumn:
Flowers: Large white flowers may be apparent, however, these do not last for long as they become covered in thousands of seeds.
Stems: When the Giant Hogweed dies, it leaves tall, brittle, brown stems in the perfect shape of the former plant. These tubular root stalks produce buds in the spring that quickly develop into the mature plants we are familiar with.
Leaves: The large jagged leaves turn yellow and shrivel up before rotting away.
Treatment: Although, when the plant has died over Autumn and Winter it cannot be treated effectively with herbicide but if the infested areas are identified then the plant can be controlled from spring onwards by a trained weed control company such as Invasive Weeds Agency. Excavation works are effective at this time of year.
Giant Hogweed stands can spread very quickly and grow over large areas as seen in the Landward video. In these instances Giant Hogweed out-competes native species and dominates ecosystems, sapping nutrients from the soil and blocking sunlight with its large leaves. Giant Hogweed has had such a damaging effect across the world that Genesis wrote a song about it (view it here) describing its devastating spread and risk it poses “Around every river and canal their power is growing…A victorian explorer found the regal hogweed by a marsh, He captured it and brought it home…Strike by night! They are defenceless. They all need the sun to photosensitize their venom”.
If you suspect that your land is infested with Giant Hogweed and you want an effective control strategy, contact Invasive Weeds Agency on 0845 676 9252 or contact us here for a free quote.
IWA. Getting to the root of the problem.