April Armstrong – Forest Research
Phytophthora austrocedri disease
of juniper
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What is Phytophthora?
• A large group of plant pathogens that infect
ornamental plants and crops of considerable
economic importance
• E.g. P. infestans – the cause of the Irish potato famine
(1845-49)
• Described a ‘fungal-like’ pathogen called an
oomycete
• Mostly water borne and persist in soil
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Phytophthoras in forestry
Approximately 100 species have been described, although 100–
500 undiscovered Phytophthora species are estimated to exist –
44 species recorded in Scotland
• P. ramorum (148 hosts)
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Including larch, rhododendron and bilberry
Air borne
Responsible for large scale felling of larch
• P. lateralis
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Discovered in Nov 2010 infecting Chamaecyparis lawsoniana in West
Dunbartonshire
Taxus brevifolia and Thuja occidentalis
• P. kernoviae (37 hosts)
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Oak
• P. alni
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alder
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P. lateralis
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Phytophthora austrocedri
• First described in 2007
associated with mortality of
Austrocedrus chilensis in
Patagonia, Argentina
• Confirmed in the UK on Juniperus
communis in 2011 by FR
• P. austrocedri in the UK is
distinctive from the Argentinean
strain of the pathogen –
alternative origin
• Found to infect Lawson cypress
and Nootka cypress
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Determining distribution in Britain
Surveys since 2011 conducted by;
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FR (research project and THDAS)
FCE and FCS Plant Health
Natural Resources Wales
FERA
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Known distribution currently confined to
Scotland and northern England (~ 100
positive sites)
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43 juniper sites surveyed in Wales –
none positive for the pathogen
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Recent finding in a shrubbery in
Southern England
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qPCR and isolation used to test samples
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Associated with wet sites
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Possible methods of spread
• Water-borne pathogen that
persists in soil
• soil tested positive
across a number of
infected sites
• Inoculum in stream and
ground water
• Explains local spread
• Juniper in remote locations
are infected
• Longer distance spread? –
aerial ? berries ?
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Natural resistance ?
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Discussion session
• Symptoms – a guide to identifying
Phytophthora austrocedri in the field
• Collecting samples
• Discussion of possible routes of spread
• Conservation implications
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Field symptoms – root/stem
infections
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Field symptoms – root/stem
infections
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Diseased phloem
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Lesion at base of stem
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Multiple stems with lesions
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Aerial branch lesion
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Aerial infections
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Range of field symptoms
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Range of field symptoms
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Range of field symptoms
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P. austrocedri
Infected J. horizontalis in Lake District
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Unlikely to be P. austrocedri
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Needle blight
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Definitely not P. austrocedri !
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Lesions
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