17 September 2009

By Bryan Irvine, Countryside Management Delivery Branch, Department of Agriculture and Rural Development (DARD)

Japanese knotweed is relatively common plant found along Northern Ireland’s waterways. It is a non-native invasive species meaning that it has come from another country and it has the potential to damage our habitats by out-competing our native plants.  

Farmers or landowners who are in receipt of Single Farm Payment and / or agri-environment scheme participants must avoid infestation of their lands by non-native invasive species under Cross-Compliance rules. Furthermore, removing non-native invasive species such as Japanese knotweed is one of the enhanced riparian zone management requirements along waterways in the NI Countryside Management Scheme (NICMS).

Japanese knotweed can be easily identified by its heart shaped leaves, bamboo-like purple speckled stems and cream flowers at this time of year.

As there are only female Japanese knotweed plants here, spread is mainly by the movement of contaminated soil material containing fragments of its rhizome (root) system or stems. Spread may also occur naturally during flood events which wash stems and bits of roots downstream.

Eradication of Japanese knotweed is difficult but achievable within four to five years of repeated herbicide application. It can be sprayed from mid to late September with the herbicide glyphosate for maximum uptake by the rhizome system. However, it will be difficult to get good coverage within the dense stands which can be over 2.5 metres in height.  It is recommended to spray once early in the growing season between April and May and the stunted growth is sprayed again in September. Follow up spot spraying will be required for several years to achieve full eradication. When spraying near a watercourse ensure you follow the directions on the product label.

For further information please check the Invasive Species Ireland website downloads section, or contact your local Countryside Management office.

Notes to Editors

All media enquiries to DARD Press Office, tel: 028 9052 4619.