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Giant Hogweed (Heracleum mantegazzianum) has hit the headlines lately with weekly tales of agony, burns and blisters. A native of SW Russia, Giant Hogweed is the big cousin of Hogweed – commonly found in grassland and meadows. It was introduced in the 19th century as an ‘exotic’ and quickly spread due to the excessive amount of seeds produced after flowering. Giant Hogweed is listed under schedule 9 of the Wildlife & Countryside Act and is also classified as controlled waste by the Environment Agency.
Identify: Easy to spot, Giant Hogweed has very large, serrated leaves, not unlike thistles, that can reach a diameter of upto 3m. It has a round, hairy and hollow stem spotted in red and can reach upto 5m in height. The flowers are white umbels that look like cow parsley on steroids. The flower heads can produce over 50,000 seeds – each seed measures 1.5cm and is the sole means of spreading and reproduction – usually carried along waterways to lodge on riverbanks.
Danger: The sap is well known to be toxic to animals and causes a photo sensitive burn in humans – sunlight and UV triggers a painful and red flare up. Sap rubbed in the eyes can even lead to permanent blindness in severe cases, however the leaves and stems have fine hairs which can also produce burns very like scalding and even permanent scarring.
Treatment
How to contain it? Needless to say any survey or treatment should be carried out in full PPE – including mask and full face shield. The hollow stem means a stem injection treatment is effective but working in close proximity amongst these plants is not advised. Spraying a herbicide presents the least risk to an operator - especially prior to flowering to stop the formation of seeds. Products containing triclopyr – such as Grazon Pro, Flail or Kaskara are very effective while a hi-load glyphosate near to water is a legal essential. Using an extended lance avoids close contact.
For help in dealing with Giant Hogweed contact Louise or Richard at Progreen or friendly advice. Email iinfo@progreen.co.uk
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