- Susceptible trees
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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. Forest Research had been researching for some time the dieback in juniper trees in Natural England’s Upper Teesdale National Nature Reserve (NNR) and at the Glen Artney SSSI in Perthshire. These studies revealed the presence of P. austrocedrae, which causes dieback and eventual plant death.
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. The current reported distribution of P. austrocedrae is limited to Argentina, Chile and the recent findings in the UK. It is not known how the pathogen entered the UK. Scientists believe it is spread by water, infected plant material and contaminated soil, making it difficult to control.
The first case of P. austrocedrae to be confirmed in Great Britain occurred in juniper bushes at the Upper Teesdale NNR in the North Pennines in England in 2011, and in single specimens of Lawson cypress and Nootka cypress trees at garden sites in Scotland. The full list of confirmed cases is now:
Cumbria - 15 sites (14 natural environment, 1 nursery)
County Durham - 4 sites (2 natural environment, 2 nurseries)
Devon - 2 sites (1 private garden, 1 nursery)
Cornwall -2 sites (private gardens)
Glen Artney, Perthshire - 1 site (natural environment)
Highland - 4 (natural environment)
Western Scotland - 2 (private gardens)
The pathogen has also previously been linked by the Royal Horticultural Society’s Advisory Service with symptomatic juniper plants found at a garden in Wales and at other sites during nursery surveys.
The impact of the pathogen is currently limited in the UK as a whole. However, it is potentially serious for the Upper Teesdale juniper, because these are rare plants and this site has the second largest population of the species in the UK. There are only about 400 hectares (1000 acres) of juniper woodland in Great Britain, most of it in Scotland. At Upper Teesdale it is protected as part of a Special Area of Conservation (SAC). Common juniper is already recognised as important and vulnerable, because over the past 25 years its extent and condition have declined considerably, especially on upland sites, where its importance is tied in with nature conservation and game management. Juniper is also a key food plant for a wide range of invertebrates and birds, and it has a unique and specialised group of associated insects, fungi and lichens. Its decline has already been attributed to overgrazing, burning, afforestation and other land use changes. The establishment of P. austrocedrae in the UK could further contribute to the decline of this ecologically important species.
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.
The natural host of P. austrocedrae in South America is the Chilean cedar (Austrocedrus chilensis). In the UK, Lawson cypress (Chamaecyparis lawsoniana), Nootka cypress (Chamaecyparis nootkatensis) and the common juniper (Juniperus communis) have now been confirmed as hosts.
A GB outbreak management team (OMT) met for the first time in September 2013. This OMT replaces the previous separate Scottish and English OMTs. Members of the GB OMT include Forestry Commission Scotland, Natural Resources Wales, Forest Research, Fera, Defra, Scottish Government, Scottish Natural Heritage, Natural England, Plantlife Scotland and Confor.
Natural England staff on the Moor House-Upper Teesdale reserve have been working with the Food & Environment Research Agency (Fera) to survey the area to establish the full extent of infection and implement biosecurity measures for anyone working on site. Removal of all infected plants in certain areas is being tried to see if it slows down or stops spread of the disease. However, there is concern that removal of plants might be of limited value and have the added risk that soil disturbance might promote further spread of the pathogen. This aspect is being monitored.
This is a significant finding, the first of its type in Europe, and Fera, Natural England, the Forestry Commission and its Forest Research agency have been working closely together to tackle the situation in Upper Teesdale.
Further site survey work will take place over 2013/14 and will be led by the results of aerial surveys that were carried out over the summer of 2013 which identified stands of potentially infected juniper bushes both in Scotland and England.
Management decisions are taken on a case-by-case basis according to the specific circumstances of the findings. Eradication is the objective where feasible, but in the case of Upper Teesdale this will not be practicable, so containment is likely to be the goal. The position will be re-assessed in light of further work, in this area and elsewhere. Treating the aerial parts of plants with pesticides is unlikely to be effective because of the nature of infection.
A Rapid Assessment (Fera website) of the need for a full Pest Risk Analysis (PRA) on P. austrocedrae has been published, and a formal consultation on its management closed on 21 September 2012.
Consultation response (Fera website)
Guidance notes on reducing the risk of causing further spread of P. austrocedrae when planting juniper or carrying out associated activities:
Imports of Juniperus and Chamaecyparis species from ‘third’ countries (non-EU countries) are banned under EU phytosanitary (plant health) legislation. Other host species are not prohibited, but must be accompanied by a phytosanitary certificate to ensure they are free from harmful organisms.
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