Skip to main content
Quick facts

Common name: none

Scientific name: Phytophthora austrocedri (previously Phytophthora austrocedrae)

What does it affect?: juniper

Areas affected so far: over 100 infected sites so far

Origin: unknown

What does Phytophthora austrocedri look like?

Symptoms include:

  • Discolouration and death of foliage. This can be uniform bronze-coloured discolouration from a root infection, or patches from lesions on the stem or individual branches.
  • Tongue or flame-shaped and cinnamon-brown coloured lesions visible underneath the bark. They can extend up to 50cm and might have associated resin pockets.

What is Phytophthora austrocedri?

Phytophthora is a genus of fungus-like soil and water-borne organisms that cause some of the worst plant health issues across the world. For example, the potato famine in 19th Century Ireland was caused by a species of Phytophthora.

P. austrocedri infects and damages the roots of trees so the plant can no longer take up water. It causes the tree to die.

Dead and dying Juniper infected by Phytophthora Austrocedri

Credit: Forest Research

What happens to the tree?

Symptoms of acute oak decline are essentially normal tree responses to stress. Thinning of leaves on the crown is caused by a tree struggling to take up water and wet patches on the bark known as bleeds can be a response to drought.

If the stress is particularly severe or prolonged, the tree can reach a tipping point where it runs out of energy to get through the winter or fight off pests. These trees can die within a few years.

Where has Phytophthora austrocedri impacted?

P. austrocedri infects trees at over 100 sites in northern England and Scotland. Juniper already has a limited distribution in the UK; the strongholds are in northern England (eg. the Lake District) and Scotland. Unfortunately, this disease can now be found in all these areas.

How did Phytophthora austrocedri get here?

We don’t know where it originated from but P. austrocedri was first described as a new species in 2007 in Patagonia, Argentina. It was then realised that this same species of Phytophthora was also in the UK and responsible for the decline of juniper at a site in Teesdale, County Durham.

This pathogen was later discovered in lots of juniper populations in the UK, so it is likely that the disease has been here for some time, perhaps over 30 years.

What impact will it have?

P. austrocedri can kill a juniper tree in as little as one or two years, but it depends on environmental conditions and the health of the tree.

There are already only around 400 hectares of juniper woodland in Britain, mostly in Scotland. It supports a specialised group of insects, fungi and lichens, as well as birds such as goldcrest, and provides winter cover for black grouse. The loss of juniper will impact all of these species.

Sadly, there is no natural resistance, but hopefully some junipers on drier sites might survive.

What are we doing about it?

To combat pests and diseases like Phytophthora austrocedri we have:

  • Developed a UK Sourced and Grown assurance scheme to make sure that all the trees we plant and sell are produced in the UK. This reduces the risk of importing new pests and diseases that could add stress to our native oaks.
  • Lobbied the government to improve biosecurity at border points to stop new pests and diseases entering the UK.
  • Partnered with Observatree, a tree health citizen science project which trains volunteers to spot pests and diseases, thereby helping tree health authorities identify and manage outbreaks early.
Horse chestnut tree discoloured to yellow after a leaf miner infestation

Trees woods and wildlife

What we are doing about tree pests and diseases

We are fighting back against pests and diseases. Find out what we're doing to prevent the spread and protect the UK’s trees. 

Learn more

What you can do

Biosecurity is very important with this type of pathogen. It is present in soil therefore it can be spread around and between sites on footwear, tyres and machinery - particularly in wet conditions because it needs water to survive. To avoid any spread, make sure to wash down your shoes and tyres of any vehicles after visiting an infected site.

More pests and diseases: