Hogweed Burns

Hogweed Burns

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Giant hogweed in the news

Giant hogweed has made headline news this year for all the wrong reasons. Not only is it considered a non-native invasive species*, but it can also cause severe skin burns and even blindness.

Giant hogweed can be found in gardens, allotments, parkland, verges, and frequently close to water courses. It’s active from spring through to autumn and over the winter the leaves die back and the tall, hollow flower-stem dries out. The period from spring to autumn is when care should be taken around this dangerous plant.

How Does Giant Hogweed Cause Burns?

The sap of Giant hogweed is phototoxic and causes phytophotodermatitis in humans, resulting in blisters and scars. If the sap is rubbed into the eyes, it can cause blindness. Contact with the sap can be caused by just brushing against the hairs on the stalks and underside of the leaves.

The affected area of the skin may remain sensitive to UV light for some years after the original burn and blisters and can be left with scars.

This year (2020), there seem to be more reports of burns caused by exposure to Giant hogweed sap. Perhaps this is due to COVID-19 lockdown and people spending more time outdoors exercising, as a result.

Giant hogweed Burns
Image 1: Burns caused by exposure to Giant hogweed sap

How to Identify Giant Hogweed

Until Giant hogweed is fully grown, it’s easy to confuse it with common hogweed.

  • Giant hogweed will grow to 4 metres tall before flowering
  • Common hogweed grows to about 2 metres tall
Giant hogweed grows up to 4 metres high
Image 2: Giant hogweed can grow up to 4 metres high
  • Giant hogweed flower umbrels have 50 or more flower stems
  • Common hogweed flower-stems are usually no more than 21
Giant hogweed flowers
Image 3: Giant hogweed has over 50 flowers per umbrel
  • Giant hogweed stems can reach up to 5 inches in diameter and are reasonably smooth. They can also develop purple blotches.
  • Common hogweed stems are rarely more than a couple of inches in diameter. In contrast to Giant hogweed, the stems are hairy all over.
Giant hogweed stems are up to 5 inches in diameter
Image 4: Giant hogweed stems can reach 5 inches in diameter
  • Giant hogweed leaves are more sharply serrated and hairless. They’re also shiny due to not having any hairs.
  • Common hogweed has smaller leaves which are less shiny due to being covered in small hairs.
Giant hogweed grows up to 4 metres high
Image 5: Giant hogweed leaves are hairless and sharply serrated

Hogweed Burn Treatment

Cover the exposed area to keep it away from sunlight and wash the sap off using soap and water or eye wash, as appropriate. Seek medical advice.

How Does Giant Hogweed Spread?

Giant hogweed is a very large, short-lived herbaceous plant. After germinating from seed the plant grows a tap root from which it can over-winter and return the following spring. The plant initially grows without flowering and typically flowers between years 2 to 3 in the months of June to August. Generally these plants don’t live longer than 5 years, and most plants completely die-off after flowering.

Each plant produces seed on a prolific scale, allowing it to colonise large areas quickly and affect the local biodiversity. The volume of seed production varies per plant though is typically around 20,000 seeds, and has been reported to be as high as 100,000 seeds.

The seeds disperse over the local area, up to 7 metres from the mother plant, with most seeds germinating the following growing season. Seeds that don’t germinate remain in the soil and seed longevity has been reported to be up to 7 years, and longer in favourable conditions.

How to Remove Hogweed

Giant hogweed can be effectively treated with herbicide, requiring successive years of treatment. Quicker results can be obtained via excavation of the plant and surrounding seed-infested soils.

Giant Hogweed: Herbicide Treatment Programme

Correct application of systemic herbicide can kill a plant outright, with the application of herbicide timed to stop the plant flowering and producing seed. Successive years of treatment are required when the surrounding soils harbour previous years' seeds. These seeds will germinate as they find space and light, requiring ongoing monitoring and treatment to infested areas, typically over a period of 3 to 5 years.

Giant Hogweed: Excavation

Giant hogweed can be excavated to provide an immediate eradication solution. This is sometimes desirable in public space areas where the plants are posing an immediate health risk. Excavation is also required where there are changes in land-use proposals for the infested area, such as a housing development. Where development, for example, will disturb the area the plant and soils containing the seed are classed as a controlled waste if removed from site.

Excavation requires removal of the plant, its deep taproot and a shallow depth of soils surrounding the plant to remove the potential seed bank.

Is Giant Hogweed Dangerous?

Yes, it is! When treating or excavating Giant hogweed, our operatives wear full PPE to avoid accidental contact with the plant. Any attempt at removing or treating Giant hogweed should only be undertaken by a professional company that understands the danger of the plant and how to deal with it.

Contact The Invasive Weed Experts

Japanese Knotweed Ltd is the UK's trusted Invasive Weed treatment and remediation company, with a proven track record in working successfully for local authorities, developers, construction companies and private landowners. Our highly knowledgeable and skilled staff provide a comprehensive service and are committed to providing the highest level of customer care.

We provide surveys and invasive weed management plans, including long term chemical treatment, guarantees, and immediate excavation options. Our remedial methods are tailored to each site and provide sensible and efficient eradication solutions to meet all requirements.

If you suspect you have a Invasive Weed problem, call us on 0333 2414 413 or email us at contact@knotweed.co.uk

Full PPE for treating Giant hogweed
Image 6: Full PPE must be worn when treating or removing Giant hogweed

*Giant hogweed is listed under Section 14, Schedule 9 of the Wildlife & Countryside Act (1981). Put simply, the UK Government has issued a list (Schedule 9) of animals and plants that are already established in the wild, but which continue to pose a conservation threat to native biodiversity and habitats. This is to such an extent that further releases of these species should be regulated.

If you wish to read more about the Wildlife & Countryside Act (1981), you can view the guidance published by the Government.

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