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Bleeding Canker of Horse Chestnut

Bleeding canker Close-up of rusty coloured exudate Serious disfigurement caused by bleeding cankers and associated bark cracking

Bleeding on the trunk and branches of horse chestnut in the UK is not a new phenomenon.  This type of symptom was first reported in the 1970s, when the cause was found to be a fungal pathogen known as Phytophthora (Brasier and Strouts,1976).  The same disorder had also been recognised in the USA much earlier in the 1930’s (Caroselli, 1953).

Incidence of the disease

Geographical location of cases of Horse Chestnut Bleeding Canker reported to Forest Research Disease Diagnosis Advisory Service

Until recently, such Phytophthora bleeding cankers were considered to be uncommon and were only seen in the south of England (Strouts and Winter, 2000).  However, over the past four or five years, the number of reports of horse chestnut trees (Aesculus hippocastanum) with 'bleeding cankers' has increased markedly.  Symptoms visible on the heavily affected trees include extensive bleeding areas on their stems and sometimes on their scaffold branches.  The increased incidence of stem bleeding on horse chestnut is not just limited to the UK; the Netherlands, Belgium, France and Germany are also experiencing a similar upsurge.

Closer investigation of the bleeding cankers on horse chestnut has revealed that Phytophthora is no longer the primary causal agent. Instead a completely different pathogen, Pseudomonas syringae pv aesculi, is responsible for the increase in these symptoms appearing on horse chestnut.

Over the past four years the Tree Health Diagnostic and Advisory Service of Forest Research has received increasing numbers of reports about the disease.  In 2000 only four reports had been received but by 2003 more than 60 reports of stem bleeding in horse chestnut were recorded.  In 2004, 90 reports were received, around 75 in 2005, and more than 110 in 2006.  Affected trees have been recorded as far north as Lancashire, Glasgow and Fife.

What trees are affected?

Trees of all ages have been affected by the recent disease upsurge.  Young trees with a stem diameter of only 10cm (4 inches) have been found with advanced symptoms.  However, the impact on the environment can be particularly profound when large, mature trees are infected and disfigured by the disease.  If the disease is severe and the areas of bark which are killed are extensive, large trees can undoubtedly be killed.  However, younger trees (10-30 years old) are at greater risk and can succumb to the disease in just a few years (3-5) as the smaller diameter of their trunks means that they can be girdled more quickly.

Detailed information


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.



Poster (PDF-852K)