- Spreads by seed with an average plant bearing about 20,000 seeds.
- Seed bank can last for up to 10 years.
- GHW grows large and forms a dense canopy which smoothers native vegetation.
- Winter die back leaves riverbanks exposed and susceptible to erosion.
- The sap from this plant is dangerous to humans reacting with sunlight and causing severe blistering and recurring dermatitis. If contact with GHW occurs:
- Keep area of skin in dark conditions, away from sunlight.
- Wash the affected area as soon as possible.
- Seek medical advice especially after contact with eyes.
- It is an offence under the Wildlife and Natural Environment Act 2011 to plant or otherwise cause Giant Hogweed to grow in the wild
Recommended methods of control.
- Spraying using knapsack sprayer and systemic, glyphosate based herbicide. Timing of spraying is important. Too early and many plants won’t have emerged from the soil. Too late and plants may already be flowering or developing seed. Our experience in Ayrshire indicates that late March/ April until early June is usually an ideal time to spray however if we experience a harsh winter it is likely that spraying will be delayed by around 1 month. Plants should be around 18″ (0.45m) tall when sprayed. Care must be taken to ensure that plants are sprayed using the appropriate strength/dilution and that the whole plant is sprayed. (when plants receive less than a lethal dose, they often survive and develop flowers prematurely as a stress response.)
- Cutting stems only delays flowering. For cutting to be effective, the plant should not have flowered and the root should be cut through at least 50mm below the soil surface. This method is suitable on scattered individual plants or where chemical application is not possible. Anyone cutting GHW should wear adequate personal protective equipment and be aware of all emergency procedures to follow should contact with the plant occur. This method should only be used as a last resort.
- Cutting/Strimming is not advisable as the risk of contact with the sap is too high.
- Grazing. Grazing is not a substitute for other treatments but it may be used in certain circumstances to assist in control. In its native range GHW is grazed on by mountain goats.
Any person spraying herbicide near a water course must have a PA6AW certificate. This is the minimum qualification required to carry out this task. (Training available through the Carrick Project for interested volunteers) Applications to SEPA in the form of a SEARS licence must also be completed to ensure permission is in place to use herbicide near watercourses. (SEARS applications will be completed by the project officer for the life span of the Carrick Project).
Download Poster here (pdf): Giant Hogweed Poster