The Department of Agriculture in Dublin is working with its Northern Ireland counterpart to prevent the spread of a virulent plant disease, commonly known as "sudden oak death", which has been found in Co Derry.
The plant fungus, known as phytophthora ramorum, was found on an ornamental plant in a private garden in Northern Ireland for the first time. It has been found in garden centres there before this discovery.
The garden is on the outskirts of Derry, but Department of Agriculture and Rural Development officials have declined to give its exact location.
A 100m-radius monitoring zone has been established around the scene of the discovery as the fungus could cause significant damage to trees and landscapes if it were to become established.
A spokesman in Belfast said the fungus normally attacked a wide range of woody plants, including rhododendron, viburnum and certain species of trees, including beech.
He said the fungus had been detected in many European countries, but this was the first time it has been found outside nurseries or garden centres in Ireland on imported planted material.
"On rhododendron, the first indication of the disease is wilting of shoots, which then develop a brown or black colour which spreads along the twig.
"Symptoms can be similar to those caused by related fungal diseases, although development of this disease may be more rapid.
"On trees, the disease can affect just the bark, as in beech, and the leaves.
"Symptoms in beech are bleeding cankers on the bark and the disease is favoured by damp conditions. The main means of spread is by rain splash," the spokesman added.
Meanwhile, plant pathologist Alistair McCracken said the discovery of the fungus was reported last week and was confirmed following a series of tests.
"All adjacent plants were removed and burnt and the roots of the infected rhododendron were taken out and buried at quite a depth.
"The area around the discovery will be monitored for the next 12 months, but we are confident that this is an isolated case," he said.