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Phytophthora austrocedrae

Phytophthora austrocedrae (P. austrocedrae) 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. austrocedrae 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. austrocedrae is a notifiable pathogen and all suspected cases should be reported to the plant health authorities.

P. austrocedrae is a species of phytophthora that was only recently ‘described’ (in 2007), although it is thought to have been present in Argentina for at least 50 years. 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 here. The current reported distribution of P. austrocedrae 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. 

Distribution

To date (2014), P. austrocedrae 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 June 2014.

Map - P. austrocedrae infections

Impact

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. austrocedrae in the UK could further contribute to its decline.

Symptoms

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. austrocedrae 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.

Susceptible trees

The host of P. austrocedrae 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. austrocedrae was introduced to South America.

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.

Action

P. austrocedrae is being treated as a notifiable pathogen. Infected sites are subject to statutory control measures involving the imposition of biosecurity protocols and restrictions on the movement of livestock, plant material and soil. Because of the rugged, wet and remote nature of many of the affected sites, destruction of infected trees is not a feasible option. Where appropriate, disinfectant mats are being used at entry/exit points from 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.

Pest risk assessment and consultation

A Rapid Assessment (Fera) has been made of the need for a full Pest Risk Analysis (PRA). A formal consultation on its management closed on 21 September 2012. 

Consultation response (Fera)

Advice and Guidance

Guidance on reducing the risk of causing further spread of P. austrocedrae when planting juniper or carrying out associated activities is available from the following documents:

Scotland

England and Wales

Our P. austrocedrae Pest Alert (see right-hand column) contains much of the information on this page in an easily printable format.

Import restrictions

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.

Reporting sightings

Tree Alert icon If the suspected case involves a number of trees in a woodland, you should report it to the Forestry Commission via Tree Alert at www.forestry.gov.uk/treealert

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 (Fera or the Scottish Government).

Please check the symptoms section above before using our Tree Alert form:

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Last updated: 10/31/2014