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Giant Hogweed

Giant Hogweed is a highly invasive plant that grows vigorously. Contact with this invasive weed produces a skin reaction that is antagonised by exposure to sunlight. Blisters occur 24 to 48 hours after exposure. Damaged skin heals very slowly, leaving residual pigmentation that can develop into recurrent dermatitis.

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How to identify Giant Hogweed

Giant hogweed is very aptly named - it really is a giant of the plant kingdom with umbrella-shaped flowering spikes growing up to 5m tall on stems over 50 mm in diameter.  Although these only appear from mid June onwards the previous year’s ‘spikes’ may remain in place too (when not blown down by winter winds or deliberately cleared away) so a big stand of Giant hogweed presents a very distinctive feature in the landscape!

Giant Hogweed - Full blossom - PCA

Giant Hogweed - looking up - PCA

Giant Hogweed - in the park - PCA

The problems caused by Giant Hogweed

The distribution and frequency of Giant hogweed is increasing over time and this is causing significant problems for homeowners and those responsible for managing public spaces due to the harmful nature of the leaves which, when touched, can cause painful blisters when the skin is exposed to the sun (so-called photo-sensitisation).

Quite apart from this feature, Giant hogweed is a major concern from an ecological point of view too.  It occupies a similar habitat to Himalayan balsam (by rivers, canals etc.) and they are often seen together.  The huge size of the leaves (2m span is not untypical) cuts-off any sunlight reaching the soil so there can be major changes to the local plant communities and all the invertebrates that depend on them.  

The law regarding Giant Hogweed

Under the Wildlife and Countryside Act 1981 and the Wildlife and Environment (Scotland) Act 2011 it is an offence to introduce giant hogweed into the wild. Although you are allowed to have giant hogweed on your own land you should take measures to limit its spread onto adjacent land. If not the adjoining landowner could take legal action against you.
 
It is also worth noting that Giant hogweed, like other ‘Schedule 9’ invasive weeds, is a controlled waste under the Environmental Protection Act and should be (together with soil containing its seeds) be disposed of at a licensed landfill site.

Controlling & treating Giant Hogweed

DIY control of Giant Hogweed is possible ‘with care’ from a health and safety point of view however, due to the risk of harm from the harmful leaves, it is not recommended.  

The plant spreads by seed dispersal so any interventions BEFORE flowering are encouraged to maximise the benefit of any control and management of the invasive plant.  However, Giant Hogweed seeds can be long-lived in the soil, so you will have to be vigilant over time to spot and remove any new plants emerging.  

In terms of control methods, there are 2 main methods: Spraying and Excavation.

  1. Spraying with herbicides is the most cost-effective treatment option, but like many invasive plants & weeds, it may take several years to be fully effective.  
  2. Excavation is a quicker method of control, but due to cost is normally only considered on development sites. If this is considered, it should be remembered that the soil/seeds and green waste all need to be handled as controlled waste.

Concerned about Giant Hogweed? There are professionals you can talk to

If you have come across Giant Hogweed and you are concerned, there are professionals that can help. Most specialist PCA invasive weed members will be happy to offer advice and guidance over the phone and, if you have pictures, will be happy to help identify and make initial assessments of the severity of the problem.

To find local PCA invasive weed specialists near you, simply run a search using the search tool below.

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