The second in our invasive species series, we turn this month to Giant hogweed (Heracleum mantegazzianum).
Listed on Schedule 9 of the Wildlife and Countryside Ace 1981 (as amended), it is an offence to plant or cause to grow, or to allow this species to spread to the wild.
How to identify Giant Hogweed
Giant hogweed belongs to the umbellifer family and it’s not difficult to see that it is a close relative of the countryside favourite, cow parsley. Originating from south-west Asia and introduced to the UK in the middle of the 19th Century, this plant is a true giant by UK standards – the stem typically grows 2-3 m high and bears umbels (clusters of short flower stalks) of flowers up to 80 cm in diameter. The basal leaves are often 1 m or more in size.
The flowers are white and all the flowers facing upwards. The stems are thick and bristly and are purple/red-blotched. This species produces a vast amount of seed (as many as 20,000 per plant), which has allowed it to spread rapidly throughout the UK. Images below courtesy of pixabay.
Giant hogweed is especially abundant by lowland streams and rivers, but also occurs widely on waste ground and in rough pastures.
What to do if you find Giant Hogweed
Be careful …
Not only does this plant out compete our native species, it can also cause danger to public health. Giant hogweed sap is highly toxic and can cause severe skin burns. When the sap comes into contact with skin it causes photosensitivity, and can lead to blistering, pigmentation and long-lasting scars. Blistering can reoccur when the skin comes into contact with sunlight for years after the original contact.
Control and removal
If this species is found on site it must be removed and disposed of as controlled waste, using a specialist contractor who is trained to work with the species. Control of giant hogweed can cause delays and additional costs to the timescales of a project if the correct methods are not followed.