Fighting The “Toxic Triffid”

Thursday 28th May, 2020

Giant hogweed (Heracleum mantegazzianumhas) has been in the news headlines recently.

Labelled “The Toxic Triffid” by the Daily Mail, this large plant (up to 20ft) of the cow parsley family (native hogweed) is often found along our rivers. Left unchecked, it can dominate large swathes of ground or rA Giant hogweed plant found in a new location on the river Arrow in June 2019. The Foundation were alerted and the plant dealt with before its seeds were spread downstreamiverbank and reduce biodiversity by out-competing native flora.

However, it is the plant’s effects on humans that is most alarming. When coming into contact with skin and in the presence of sunlight, its sap causes a rash which is often followed by severe burns and blistering welts.

This condition is called ‘phyto-photodermatitis.’ The burns can last for several months but even after they have reduced the skin can remain sensitive to light for many years afterwards. The sap can also cause blindness if it comes into contact with the eyes.

Without the Foundation’s Giant hogweed eradication programme, it is likely that many more anglers and other people that enjoy the riverbanks would have suffered the painful and potentially life-changing effects of a brush with this plant

Like many invasive plant species, we have the Victorians to thank for Giant hogweed, who introduced it to the British Isles in 1893 from the Caucasus.

In 2007 the Foundation set about dealing with the problem in the Wye and Usk. With support from the Esmee Fairbairn Foundation, we began a programme to eradicate this dangerous plant from our riverbanks. Every spring a sweep of the two rivers is carried out, spraying any plants we find before they flower and seed. This is then followed by a boat survey during which any flowering plants missed earlier in the year or inaccessible from the bankside are deadheaded.

Wye & Usk Foundation staff spraying invasive and noxious Giant hogweed plantsCovered head to toe in protective clothing, this is a task we can carry out while complying with COVID19 precautions!

While the plant is still a problem for the lower sections of the Usk, thirteen years on much of both river corridors are now mostly free of Giant hogweed.

However, its seeds can remain viable in the soil for more than eight years before germinating. This is why we need to check both rivers every year. New plants can appear in places we believed to be clear, often on ground disturbed through flooding or animals. Newly uncovered seeds germinate once exposed to daylight.

In addition to improving biodiversity along our riverbanks, it is highly likely that without this eradication programme many more anglers, canoeists and walkers would have suffered the painful and potentially life-changing effects of coming into contact with this plant.

We would like to thank the Esmee Fairbairn Foundation for supporting this programme along with Dwr Cymru Welsh Water, Natural England, Environment Agency and Natural Resources Wales.

Don’t touch it, report it!

If you come across a plant that looks like a large cow parsley, please do not under any circumstances touch it.

If it is on a riverbank in the Wye or Usk catchments, please take a photo and email it to us with as close a description as possible of its location. The What3words app is especially good for recording and reporting the location of Giant hogweed and other invasive plants.

Read more about battle against Giant hogweed and other invasive plants….

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