- Susceptible trees
- Policy, pest risk assessment
- Advice and Guidance
- Import restrictions
- Reporting sightings
Phytophthora austrocedri (P. austrocedri) is a fungus-like pathogen which poses a threat to juniper trees in Britain. Juniper (Juniperus communis) is an important native species, and a significant proportion of the small area of juniper woodland in Britain is protected. P. austrocedri was first reported in the UK in 2011, and infected trees have since been found at sites across Scotland and the north of England. The pathogen primarily attacks juniper roots, killing phloem and forming lesions which extend up into the lower stem. Eventually the tree will be killed by girdling of the main stem. P. austrocedri is a notifiable pathogen and all suspected cases should be reported to the plant health authorities.
P. austrocedri is a species of phytophthora which was only recently ‘described’ (in 2007), although it is thought to have been present in Argentina for at least 50 years. The name ‘austrocedri’ 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. austrocedri, 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. austrocedri in the UK are the first confirmed findings of this pathogen here. The current reported distribution of P. austrocedri is limited to Argentina and 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.
To date (2015), P. austrocedri has only been recorded in Argentina and Britain, and its geographical origin and global distribution are currently unknown. It was first described in Argentina in 2007, where it was associated with the widespread dieback and mortality of the native Chilean cedar (Austrocedrus chilensis), which is also known as Patagonian cypress and Cordilleran cypress. In 2011 it was reported in Great Britain for the first time, and it is now known to be widely distributed on juniper trees in the Cairngorm region of Scotland and the Lake District in the north of England, where juniper is relatively abundant. The first case to be confirmed in Britain was in juniper bushes at the Upper Teesdale National Nature Reserve in the North Pennines in England in 2011. More juniper sites in Scotland, England and Wales were under investigation in 2014.
The map below shows confirmed cases at November 2016.
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. The Native Woodland Survey of Scotland identified 1,482 hectares containing juniper scrub in Scotland, but there are no reliable statistics currently available for England and Wales. 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 since about 1990 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. austrocedri in the UK could further contribute to its decline.
Foliage on infected trees turns bronze/brown over all or part of the crown. The pathogen also occasionally attacks the stem or branches, so that the foliage associated with that particular infected branch or stem turns bronze/brown.
Wood/bark - When the outer bark of the tree is cut away at the infected area, discoloured phloem (inner bark) is revealed. The diseased tissue is usually cinnamon brown in colour, often with a distinct yellow colouration at the lesion edges, whereas healthy phloem is white.
P. austrocedri symptoms can be confused with those of other infections, including those caused by other Phytophthora species, such as P. cinnamomi, 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 host of P. austrocedri in South America is the Chilean cedar (Austrocedrus chilensis), on which it causes a disease known in Spanish as mal de cidres (cedar disease). However, the available evidence suggests that P. austrocedri was introduced to South America from elsewhere.
In the UK, juniper is the main host, but Lawson cypress (Chamaecyparis lawsoniana) and Nootka cypress (Chamaecyparis nootkatensis) have also been confirmed as hosts, although the number of reported infections of these species is small.
P. austrocedri is a notifiable pathogen, and statutory action is taken on findings in the nursery trade – usually destruction of infected stock. In the wider environment, the plant health authorities work in collaboration with conservation organisations and other stakeholders to protect unaffected areas where possible. At known infected sites, they work in collaboration with conservation organisations, land managers and other stakeholders to minimise the risk of spread. (See also ‘Policy, Pest Risk Assessment and Consultation’ below.)
Because of the rugged, wet and remote nature of many of the affected sites, destruction of infected trees is not feasible. Where appropriate, disinfectant mats are used at entry/exit points at sites with high levels of public access, and staff and visitors are asked to use them to kill any spores from the pathogen which they might pick up on footwear. Notices have also been erected at these public sites to inform visitors of the infection and to encourage them to observe sensible biosecurity measures, such as keeping to the footpaths, keeping dogs on leads, and cleaning shoes and boots after leaving the sites.
In 2015 the Chief Plant Health Officer reviewed government policy on P. austrocedri management in consultation with interested parties. The key decisions from the review were to:
- end statutory controls in the wider environment, other than in exceptional circumstances, but maintain statutory action against findings on nursery plants for movement; and
- continue to work in collaboration with conservation organisations and other stakeholders to protect unaffected areas where possible and, at known infected sites, continue to work in collaboration with conservation organisations, land managers and other stakeholders to mitigate the risk of spread.
Guidance on reducing the risk of causing further spread of P. austrocedri 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.
If the suspected case involves a number of trees in a woodland please check the symptoms section above before reporting it.
If you are a nursery owner or involved in a business handling young trees and plants, you should report suspected cases on infected trees to the relvant plant health authority (APHA or the Scottish Government).