Forestry Commission Scotland is advising landowners and managers across Scotland to be on the alert for a plant health threat to juniper.
Phytophthora austrocedrae is a fungus like pathogen that was only recently (2007) identified in Argentina and Chile, where it is believed to have been causing disease in their native Chilean cedar since the mid-20th century. It infects the plants through their root systems, initially
leading to discolouration and loss of foliage but ultimately resulting in the death of many affected trees.
In 2011 the pathogen was identified as the cause of disease in juniper bushes within the Upper Teesdale National Nature Reserve in England and in single specimens of Lawson cypress and Nootka cypress trees at two sites in Scotland.
The presence of Phytophthora austocedrae has now been confirmed at several other sites in northern England and at Glenartney Juniper Wood Site of Special Scientific Interest (SSSI) in central Scotland.
Hugh Clayden, FCS’s tree health policy adviser, said
“This development is of concern because juniper is quite rare in Britain. Around 80% of Britain’s surviving juniper population is in Scotland and - as a priority species – it is the focus of significant conservation effort.
“This newly discovered pathogen has the potential to harm not only the juniper population but also the unique and specialised group of associated insects, fungi and lichens for which juniper is a key food plant.
“An Outbreak Management Team, which draws on a wide range of expertise, has been set up to agree how best to manage this disease at Glenartney. As a result, a containment notice has been issued and no plant material or soil will be permitted to be removed from the site. All field staff and individuals working on the site will also adopt biosecurity measures to prevent further spread of this pathogen.”
Surveys will also be carried out at other key juniper sites in Scotland to see if this disease is present, and any other affected areas will need to be managed appropriately after discussion with landowners and other stakeholders.
It is not known how the pathogen entered the UK but it has the potential to be moved in soil from infected sites and on host plants such as Chilean cedar, Lawson cypress and Nootka cypress. Scientists believe it can also be spread in water, which makes it even more difficult to control.
Above-ground symptoms on infected bushes include discolouration and death of the foliage and the presence of ‘tongue-like’ lesions in the inner bark at the bases of their stems. The foliage of infected trees and bushes initially becomes slightly lighter in colour and may have a yellow cast but it rapidly turns bronze and finally light brown. These changes reflect progressive death of the inner bark at the base of the stem which dries and darkens as it is killed by the pathogen.
It is easy to confuse the symptoms caused by Phytophthora austrocedrae with those of other diseases so expert involvement is required to obtain an accurate diagnosis.
Anyone in Scotland who finds suspicious symptoms on juniper, Lawson cypress or Nootka cypress should report them to the Tree Health Diagnostic and Advisory Service at email@example.com or contact the Forestry Commission’s Plant Health Service on 0131 445 2176.
1) Forestry Commission Scotland is part of the Scottish Government’s Environment & Forestry Directorate.
2) Glenartney Juniper Wood SSSI is also designated under the EC Habitats Directive as a Special Area of Conservation.
2) In the UK, Lawson cypress (Chamaecyparis lawsoniana), Nootka cypress (Chamaecyparis nootkatensis) and the common juniper (Juniperus communis) have been confirmed as hosts of Phytophthora austrocedrae.
3) Phytophthora austrocedrae has also been linked by the Royal Horticultural Society’s Advisory Service with juniper plants at a garden in Wales and at other sites during nursery surveys.
4) Media Enquiries to Paul Munro, Forestry Commission Scotland press office, 0131 314 6507.
P. austrocedrae is a species of Phytophthora that was only recently ‘described’ (in 2007), although it is thought to have been present in Argentina and Chile for at least 50 years. It is a fungus-like plant pathogen which causes an often fatal disease of its host plant. The name ‘austrocedrae’ originates from Austrocedrus, the genus of conifer trees first recorded as a host (i.e. a plant capable of being infected) of this pathogen in Argentina. The recent discoveries of the pathogen are a concern because of the often fatal nature of infection of the host plant, and because the recent findings of P. austrocedrae in the UK are the first confirmed findings of this pathogen in the UK.
P. austrocedrae was confirmed in juniper bushes at the Upper Teesdale National Nature Reserve (NNR) in the North Pennines in England in 2011, and in single specimens of Lawson cypress and Nootka cypress trees at two sites in Scotland. In 2012 it was confirmed in juniper plants in Cumbria in North-West England; at Glen Artney in Perthshire, Scotland; and in a nursery and a private garden in Devon in South-West England. Meanwhile, other juniper sites showing possible symptoms are being investigated in South-East England.
Above-ground symptoms on infected trees include dieback of the foliage, stem and collar lesions. The root/collar infection is described as ‘tongue-like’; this can be observed by removal of the outer bark, whereupon the phloem is necrotic, often cinnamon brown, with a distinct margin between diseased and healthy tissue. When roots and collars/stem bases are affected, foliage of infected trees initially appears a slightly lighter colour than that of healthy trees. Later the foliage withers, turns bronze, and finally, light brown, concurrent with drying and darkening of the inner bark.
Disease symptoms caused by P. austrocedrae can be confused with other infections, including those caused by other Phytophthora species, such as P. cinnamomi, a pathogen which is already present on a range of host plants in the UK and around the world. Physical damage caused by heavy snow or drought might result in similar browning of the foliage, but there would be no associated lesions.