Catchment News

Battling the invaders in Duhallow

There is a war being fought across Duhallow to control the alien invasive plant species Japanese knotweed. IRD Duhallow’s RaptorLIFE project has committed a huge amount of time into trying to eradicate this plant within Duhallow (located in North Cork and East Kerry). RaptorLIFE is a 4.5 year programme (2015-19), whose overarching objective is to bring local communities together to achieve a better environment for everyone within the region. They are doing this by connecting and restoring upland habitats for hen harrier and merlin, as well as freshwater habitats for Atlantic salmon and brook lamprey. A large part of this restoration work involves the control of invasive species.

The invasive plant, Japanese knotweed is now common across Ireland, particularly along rivers, roads and on waste ground. It blocks routes used by wildlife to disperse, damages flood defence structures and leaves riverbanks exposed to erosion when it dies back in winter. Not only an environmental problem, Japanese knotweed can seriously damage houses, buildings, and infrastructure by growing through concrete, tarmac and other hard surfaces. For example, knotweed costs the UK economy an estimated £166 (€186) million per year for treatment and home devaluations.

The spread of Japanese knotweed is a global problem and whether it can be eradicated in Ireland is debatable. Eradicating invasive species is an attainable goal if new infestations are detected early. However, eradication might not be feasible when populations are large and widespread. A more realistic management goal for knotweed could be to control the plant by reducing its density and abundance to a level that does not compromise the integrity of the ecosystem and allows native species to thrive. In this case, control strategies must strike a balance between the ecological impacts of allowing invasive species to spread and the economic considerations of control measures. The UK is trialling a number of novel control methods including the introduction of a tiny sap-sucking psyllid bug, which has been found to inhibit the growth of Japanese knotweed, leaving it weakened and less able to exploit its invasive abilities.

In 2016, RaptorLIFE treated 367 stands of knotweed on Duhallow roads and riverbanks. In 2017, this effort was significantly increased with 644 stands of knotweed treated. Knotweed can be controlled successfully through the application of appropriate herbicides (typically glyphosate); however, eradication of the plant usually takes several years depending on the size of the infestation. Data on successful eradications in Ireland is limited so RaptorLIFE are trialling a number of methods and recording important information about each stand including its size, location, method of treatment, and the proportion of the stand that died following treatment. While the 2017 data is still being collated, preliminary results show that the proportion of the stand killed following treatment in 2016 varied between 50 to 100%, with spraying more effective than the stem injection method. While RaptorLIFE have won this years’ battle against knotweed, whether they win the war is another story.

RaptorLIFE would like to acknowledge and thank all of the landowners, supporters and volunteers for their assistance with the project to date. If you would like further information or to participate as a volunteer, you can contact them on Tel: 029-606 33; Email john.ballinger@ irdduhallow.com; Website www.duhallowlife. com/raptor-life or Facebook www.facebook.com/ IRDDuhallowLifeProject/

John Ballinger, RaptorLIFE Project Scientist