Bleeding Canker on a Horse Chestnut Tree

Horse Chestnut Bleeding Canker – Pseudomonas syringae pv. aesculi

Pests and Diseases

15th May 2023 | Info

Common Name: Horse Chestnut Bleeding Canker

Scientific Name: Pseudomonas syringae pv. aesculi

Type: Bacterial Pathogen – Disease

Affects: Horse Chestnut (Aesculus hippocastanum)

Current Impact: Across the UK

Origin: Unknown


The Horse Chestnut Bleeding Canker (Pseudomonas syringae pv. Aesculin) is a bacterial pathogen that is currently significantly impacting the Horse Chestnut population in the UK.

The pathogen was first recorded in the UK in the 1970s but became increasingly more common in the early to mid-2000s.

What does it do?

When a tree becomes affected by the pathogen, bacteria begin to multiply within its water transport system that can be found beneath its bark. This eventually can lead to a tree’s untimely death as they are unable to take up any water.

This process can also cause the thinning and dieback of crowns.

Each infected tree will vary in severity, and not all cases will end in a tree’s death. You will often find that many trees remain healthy for years while infected, while others can die within the first few years of infection.

A study in 2017 found that presence of the disease was associated with a loss of microbial diversity within the affected trees.

What is the current impact of the disease?

According to the Woodland Trust, a survey carried out in 2007 identified that over half of the trees surveyed within England, Scotland and Wales were infected by the pathogen.

What symptoms should I look out for?

Both young and old Horse Chestnut trees can be affected by this bacterial pathogen. You should keep an eye out for the following:

  • Cracking in the bark that bleeds a sticky liquid – one of the most apparent symptoms. If you spot cracks in the bark of a Horse Chestnut tree with a dark red-brown liquid seeping out, then this could be a sign of the bacterial pathogen. In colder months, the liquid can dry out and leave behind a rusty deposit.
  • Discoloured wood – Healthy wood of a Horse Chestnut tree is often a white to pinky-white colour. However, underneath the bark of infected trees, you may spot patches of dark brown-purple decolouration.
  • Exposed wood – The bark of trees that have been infected for a long time may fall off to reveal the wood beneath it.
Close up of Chestnut Bleeding Canker
Close up of the bark of a Horse Chestnut Tree showing the bark is cracked and bleeding from having bleeding canker disease

What can I do if my tree is infected? How can we combat it?

In the UK, there is currently no chemical treatment approved to cure/treat the development of bleeding cankers.

Forest Research say that the complete removal of an infected tree is not necessary to prevent the further spread of the pathogen. Instead, consideration should be taken to remove any branches that show any significant signs of infection or dieback. This comes after recent developments which have shown that dead branches of a Horse Chestnut can suddenly fracture and fall.

The general guidance for trees that are affected by the Horse Chestnut Bleeding Canker is to manage it as you would with other bleeding cankers.

Additionally, as with all pests and diseases, organisations such as the Woodland trust are pioneering for tightened biosecurity to be implemented with the aim to stop new ones from entering the UK.

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