Case Study:

Eradicating Invasive Alien Species

Background

Limerick City & County Council has been engaged in the collection of data and awareness raising in relation to invasive alien species in the city and county for a number of years. This work has highlighted the serious problem of giant hogweed in the River Maigue Catchment. This infestation has its origins in the River Loobagh, which is one of the tributaries of the Maigue. A comprehensive exercise has been undertaken by Limerick City & County Council to map the extent of giant hogweed in the River Loobagh catchment. This has shown the infestation to be more widespread than previously thought. This data was captured in the field using geospatial applications, including both a QGIS field app and a “Report Invasive Plants” smartphone app, which was developed by Limerick City & County Council in 2016.

Solution

In order to tackle the infestation, Limerick City & County Council successfully applied to the Department of Culture, Heritage and the Gaeltacht under National Biodiversity Action Plan funding for biodiversity projects to undertake a three-year control programme for giant hogweed on the Loobagh Catchment. The overall objective of the programme is to achieve complete control and possible long-term eradication of giant hogweed in the Loobagh Catchment. Limerick City & County Council highlighted the need to engage experts in invasive alien species whose methodology would move away from the more conventional approach to control, which is to spray with herbicide up to four times a year. This approach is different from conventional eradication programmes in several respects: herbicide will not be used unless there are no other options; habitat restoration to prevent colonisation by secondary plant invaders (e.g., Japanese knotweed) will be prioritised; and, the community will be encouraged to engage through citizen science and active participation (Figure 1).

The eradication programme has two main phases:

1) reduce the seed bank by cutting seeds from the plants before they ripen and disperse, and,
2) dig up the tap roots in early spring. The success of this approach is dependent on systematic removal of seeds and plants from the top of the catchment downstream: even one plant left in the upper catchment could lead to recolonisation along the entire length of the catchment.

Benefits of solution

Environmental
Conventionally, herbicide spraying is repeated year on year until the seed bank is exhausted and it could lead to unacceptable levels of chemicals in the environment. When giant hogweed is treated with herbicide the plant is killed, along with some of the surrounding vegetation, and this leaves bare, exposed soil, which is subject to erosion and is therefore vulnerable to colonisation by other invasive alien species. For example, giant hogweed is frequently replaced by hybrid butterbur, and this leads to a continued degradation of habitat and loss of biodiversity. It is for these reasons that a non-herbicide approach is being taken in this eradication programme. The eradication programme methodologies being undertaken by the contractors vastly reduces the amount of herbicide introduced to the environment and the reseeding of exposed areas prevents colonisation by other invasive plants.

Economic
Remediation to mitigate erosion of riverbanks will be reviewed and discussed with individual landowners.

Social
Giant hogweed represents a serious risk to public health. Contact with the plant’s toxic sap can cause painful burns/blisters. Eradication of giant hogweed from the Loobagh catchment will prevent members of the public from accidental exposure to the plant. In addition, a number of public meetings throughout the project will help educate local stakeholders in relation to the identification and control of giant hogweed.

Figure 1: Removal of giant hogweed in Co. Limerick.

Project Details:

Timeframe/timescale
The programme commenced in Q3 2019 and will be completed by 30th September 2021.

Local authority project contact
Sharon Lynch
Environmental Technician
Limerick City & County Council
Merchants Quay
Limerick
V94 EH90