Understanding the threat posed by Phytophthora austrocedri to juniper in Britain

Juniper treesPhytophthora austrocedri is causing widespread mortality of native juniper in northern Britain. This project aims to provide the evidence base to guide juniper conservation strategies that mitigate the effects of the pathogen. 

Research objectives

  • Evaluate the genetic diversity of P. austrocedri to determine whether it is a recent introduction to Britain, how long it may have been evolving here for and to elucidate, if possible, ‘source’ populations and routes of spread.
  • Develop a greater understanding of the epidemiology of P. austrocedri by defining optimum conditions for growth and survival and by identifying mechanisms of spread.
  • Determine the wider distribution of the pathogen in Britain, linking disease severity with key site factors (soil type, wetness, climate, human activity). 
  • Determine whether natural resistance occurs in the juniper population and whether this could form the basis of a resistance breeding programme.

Results so far

Phytophthora austrocedri has very little genetic diversity in Britain and is therefore almost certainly a fairly recent introduction. The British strain of the pathogen is genetically distinct from the strain causing widespread mortality of Chilean cedar in Argentina and the geographical origins of the epidemics in both countries remain unknown. P. austrocedri grows best at 15°C and is killed at temperatures of 22.5°C and higher. This pathogen is widespread on juniper in many parts of Scotland and northern England and its DNA is readily detected in soil at infected sites. P. austrocedri DNA is also detectable in stream water and ground-level rain traps. Observations of healthy trees within high mortality sites suggest that there may be some resistance or tolerance in juniper to P. austrocedri. A provenance/progeny trial of juniper was established in autumn 2015 with seed collected from fifteen geographically separate locations across Britain. The long term goal of this trial is to assess genetic diversity in juniper and whether heritable resistance to P. austrocedri exists.


This project started in 2015 and will run until 2019

Related services

To report a possible finding of P. austrocedri on juniper to Forest Research scientists please use TreeAlert

Related resources

P. austrocedri page on the FC site

P. austrocedri Pest Alert

P. austrocedri Factsheet

Phytophthora austrocedrae emerges as a serious threat to juniper (Juniperus communis) in Britain (Plant Pathology)


Sarah Green

Funders and partners

Funded as part of the Forestry Commission Programme 2 ‘Understanding Biotic Threats’ and by Forestry Commission Scotland.
In collaboration with NERC Centre for Ecology and Hydrology (CEH)

Forestry Commission policy

This research underpins the evidence base for the delivery of healthy and resilient forests and wider ecosystems which is part of the Tree Health and Plant Biosecurity Action Plan