Alien invasion of knotweed takes root across nation

A parish just outside Cork City is one of many urban and rural communities under threat from an invasive alien species.

Japanese knotweed is in the top 100 list of the Global Invasive Species Programme (GISP) and has taken a grip on communities such as Glounthane.

The knotweed plant has vigorously invaded natural habitats, hedgerows and waterways all over Ireland and pushed out our own native species, leading to huge areas of monoculture where no other species can survive and the biodiversity in the area is greatly reduced.

In recent years, over 3,000 reports of the troublesome plant have been filed by the National Biodiversity Data Centre from all over the country. Huge chunks of Leinster from Wicklow to south Kilkenny, along with most Munster and Ulster counties are affected. Data suggests the weed has taken root in over 550 areas of 10sq km and over 120 areas of 50sq km.

According to GISP’s mission statement: “The spread of invasive alien species — non-native organisms that cause, or have the potential to cause, harm to the environment, economies, or human health — is creating complex and far-reaching challenges that threaten both the natural biological richness of the earth and the well-being of our people.”

The knotweed has been identified in Ireland as one of the worst, and highest risk, invasive, non-native, species. The problem is, once established, it is extremely difficult to eradicate.

In Glounthaune, about 7km from Cork City, there is almost continuous infestation between Dunkettle and the Killacloyne Bridge leading into Little Island.

Even though there is no apparent management plan by Cork County Council or budget to deal with this infestation, it would be all too easy to lay the blame there.

The solution is much more complex as it is a problem facing local authorities all over Ireland and Britain.

The only relatively knotweed-free area is in the centre of Glounthaune along the Ashborne walkway where there has been a concerted campaign of spraying, over several years by the Tidy Towns committee.

Glounthaune has a vibrant community association and an active Tidy Towns group. However, in the recent Tidy Towns’ adjudication, the amount of Japanese knotweed was described as “astonishing”.

The control of the alien species is seen as beyond the work of community groups alone. In the same way as it cannot exclusively be a local authority issue, it cannot fall entirely on voluntary effort. A multi-pronged approach is needed combining local authorities, NRA, Irish Rail, local communities and perhaps local business to tackle this challenge.

Local resident and Tidy Towns member Gary Tomlins is concerned about the unwanted invader: “Verge cutting management practices by the county council of flailing the undergrowth is actually spreading the knotweed and is probably responsible for the linear infestation.

“This practice places the county council at risk of prosecution for spreading the knotweed. Under the relevant EU directives, Glounthaune Tidy Towns believes community involvement is required in tackling the problem and we have made a proposal to the county council proposing an investigation into methods of control and to cooperate to find a sustainable model for other communities.”

Mr Tomlins said: “The response to our proposal by the council has been disappointingly low key. We do not believe the council is showing leadership or ownership here. Our proposal included an offer of investment of time, effort and resources.

“We are concerned that the spread now is so extensive and the growth exponential that unless leadership is undertaken by the council we will have a very extensive problem and that adjacent infrastructure and property will be devalued or damaged.”

- Peter Dowdall is a Cork-based gardening designer, commentator and a contributor to the Irish Examiner’s Weekend magazine.

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