Bleeding Canker of Horse Chestnut

Serious disfigurement caused by bleeding cankers and associated bark cracking

Bleeding canker is a disease that affects horse chestnut trees (Aesculus hippocastanum). It was first reported in Britain in the 1970s, although it was recognised in the USA much earlier in the 1930s. Pre-2000, symptoms of the disease were associated with two Phytophthora pathogens.

Today, the incidence of the disease within the UK has increased dramatically.  In 2000 only four cases were reported but this rose to more than 110 reports in 2006 and survey results show that in 2007 around half the horse chestnut trees in Britain showed some degree of symptoms. The causal agent is now most often due to a bacterial pathogen, Pseudomonas syringae pv aesculi, and only very occasionally caused by Phytophthora.

This resource will help you to identify bleeding canker disease and select a suitable management strategy.

Details of the disease

  • Trees of all ages are affected and can die
  • Cankers and bark cracks on the stem
  • Bleeding on the trunk and branches

Find out more about the symptoms of bleeding canker.

Although it mainly affects horse chestnut trees the symptoms of bleeding canker can affect other tree species and be caused by different pathogens. For example, some root diseases can present with similar symptoms such as bleeding on the lower trunk and root flares. 


Close-up of rusty coloured exudateOur research has shown that the increase in incidence in horse chestnut bleeding canker has been caused by a new and recently arrived pathogen, Pseudomonas syringae pv aesculi, [Link to sub-page on causal agent].

Until 2000, bleeding canker thought to be caused by two fungal-like pathogens: Phytopthora cactorum and Phytophthora citricola (now called P. plurivora). Instead Pseudomonas syringae pv aesculi  is now the most frequent cause of bleeding canker symptoms on horse chestnut.

Disease management

Bleeding cankerConfirming the cause of symptoms of bleeding canker on horse chestnut is critical to any recommendations about effective control measures. Surveys are also recommended to assess the number and condition of affected trees.

There is no chemical treatment currently registered or approved for use in the UK to cure or arrest the development of bleeding canker caused by Pseudomonas syringae pv aesculi:

  • If cankering lesions become extensive the entire trunk may be girdled and the tree will inevitably die and have to be removed.
  • Consider removing major branches that are infected and show dieback. Recently-dead branches of horse chestnut may be susceptible to sudden fracture and drop as the wood dries out.
  • Trees with bleeding cankers on the trunk can still have healthy-looking crowns and may not pose an immediate safety risk.
  •  Some trees may survive for many years as disease progression can be very slow or even show signs of recovery (vigorous callus development at the margins of cankers when bark has been killed by the disease).
  • Removing affected trees can be unnecessary. Significant numbers of trees do recover.

Find out more about how to manage bleeding canker. You can also review specific recommendations for managing bleeding canker of horse chestnut and find out how to dispose of infected tree material and replant after an infection .

Our research

Forest Research scientists have identified the bacterium that is responsible for the increase in incidence of bleeding canker disease on horse chestnut. Researchers are now using molecular technology to characterise the biology of this pathogen .

Scientists are also exploring the impact that other Phytophthora species have on the health of trees.

Related resources


For further information please contact:

Dr Joan Webber

or the Tree Health Diagnostic and Advisory Service.


What's of interest

Collecting information

Before embarking on any control measures it is important to assess the number of affected trees, their location on the site and extent of the symptoms on individual trees.

Survey results (PDF-348K) from Forestry Commission horse chestnut survey.

See also the Surveying page. This includes a form to use if you want to carry out your own horse chestnut survey.