Extent of the bleeding canker of horse chestnut problem

Bleeding canker of horse chestnut: Disease Incidence

Reports and survey results show that the incidence of the bleeding canker is increasing

Bleeding canker of horse chestnut trees (Aesculus hippocastanum) was – until recently – considered to be a rare disease restricted to the south of England. In 2000 only four cases were reported but this rose to more than 110 reports in 2006. Since then, the disease has been reported from throughout the UK and also in the Republic of Ireland.

Forest Research scientists now estimate that more than 50,000 trees are affected and many have been felled because they are so debilitated by the disease.

Survey results show disease is widespread

In 2007, The Forestry Commission undertook a survey to assess how widely trees in Britain are affected by the upsurge in bleeding canker. Survey results show that the disease was widespread with around 49% of all trees assessed showing symptoms to some degree. The results also showed that the disease incidence varied in different parts of Britain.

Percentage of horse chestnut trees surveyed in 2007 with symptoms of bleeding canker
RegionRural locationsUrban locations
Northeast 46% 33%
Northwest 54% 64%
Yorkshire and Humber 39% 37%
East Midlands 35% 47%
West Midlands 38% 87%
East of England 33% 59%
Southeast 79% 74%
London 47% 49%
Southwest 52% 58%
Wales 32% 41%
Scotland 34% 50%




Percentage of horse chestnut trees surveyed in 2007 with symptoms of bleeding canker.

A regular annual survey of around 230 horse chestnuts in Hampshire has shown that at least half of the trees have developed bleeding canker symptoms. A higher proportion of trees in towns and rural areas are affected compared with woodland trees, while more red horse chestnuts (Aesculus x carnea) are affected than white-flowered trees (Aesculus hippocastanum). 

Incidence in Europe

However this dramatic increase in incidence is not restricted to the UK: the Netherlands, Belgium, France and Germany have seen a similar upsurge. At least one third of horse chestnuts in The Netherlands are affected by bleeding canker.

What is causing the increase?

Close investigation shows that Phytopthora pathogens are no longer the primary causal agents of bleeding canker. Instead a completely different pathogen, a bacterium called Pseudomonas syringae pv aesculi, is responsible for the increasing incidence of the disease. Find out more about the increase in incidence and the causal agents of bleeding canker.