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Quick facts

Common name: none

Scientific name: Phytophthora lateralis

What does it affect?: Lawson cypress, sometimes juniper and western red-cedar

Areas affected so far: across the UK

Origin: thought to be Asia

What does Phytophthora lateralis damage look like?

Symptoms include:

  • Lesions under the bark which are tongue-shaped and cinnamon-brown in colour.
  • Resin bleeding on the outer bark which might be a sign of lesions underneath.
  • Foliage changing colour from green to reddish-brown.
  • Foliage death. This can be across the whole tree or on individual branches.
Phytophthora Lateralis lesions at the base of Lawson cypress tree

Credit: Ana Perez Sierra / Forest Research

What is Phytophthora lateralis?

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

P. lateralis infects and damages the roots of trees so it can no longer take up water and nutrients, killing the tree.

Where has Phytophthora lateralis impacted?

P. lateralis was first discovered in the UK in 2010. There are some isolated reports of it across England and Wales, but it is more common in Scotland and Northern Ireland.

It has recently been found in other parts of Europe too but has been present in North America, where Lawson cypress is native, for decades.

How did Phytophthora lateralis get here and what impact will it have?

P. lateralis most likely arrived via infected plants imported from Europe. Four confirmed outbreaks on mature trees were found next to nurseries, garden centres, and plant sales areas.

It can spread very easily via soil and water on footwear, tyres and machinery. Trees that are infected rarely recover and normally decline and die quickly.

Commercial imports of Lawson cypress from Europe continue, and while they are checked by authorities for symptoms, it is likely that the pathogen is spreading via the potting soil. This means that the spread is likely to continue.

What are we doing about it?

In some cases where there is a risk to sensitive natural habitats or an isolated case is found in a new area, government authorities will destroy the infected trees and monitor the area.

To combat the spread of pests and diseases like Phytophthora lateralis 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. 
  • 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 to do if you spot it

If you think you've spotted the signs and symptoms of this disease, you must report them to the plant health authorities via TreeAlert if you are in Britain or TreeCheck if you are in Northern Ireland.

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