Emerging Pest Alert

Update on Bleeding Canker of Horse Chestnut (UK & Europe)

Scientific Name: Pseudomonas syringae pv. aesculi

Describer: nan

Common Name: Bleeding Canker of Horse Chestnut

Title: Update on Bleeding Canker of Horse Chestnut (UK & Europe)


Significance: A new and more aggressive bleeding canker disease of horse chestnut (Aesculus hippocastanum) was first observed in parts of the UK and Europe around 2003. Since then, the incidence of this disease has risen markedly in the UK, where it is now found in England, Scotland, and Wales. Researchers observed a similar upsurge in Europe where the pathogen is causing dieback and tree mortality in the Netherlands, Belgium, Germany, France and Italy.

Until just recently the causal agent of this disease was not certain. UK researchers found, through various tests and the application of Koch’s Postulates, that a single strain of Pseudomonas syringae pv. aesculi is responsible for the disease. Previously this pathovar had only ever been reported from the foliage of A. indica in India. The impact of the bacterium on A. hippocastanum in the UK appears to be widespread and damaging.

Issues of Concern: This bleeding canker disease of horse chestnut appears to be increasing in both prevalence and importance in the UK and Europe. The pathogen is not known to occur in North America. Aesculus hippocastanum is native to Europe, but is grown as an ornamental tree in temperate regions of North America.


Webber, J.F., N. M. Parkinson, J. Rose, H. Stanford, R. T. A. Cook, and J. G. Elphinstone. 2008. Isolation and identification of Pseudomonas syringae pv. aesculicausing bleeding canker of horse chestnut in the UK. Plant Pathology Vol. 57:368.

Mabbett, T. 2007. Bacterial bleeding canker beyond doubt. Forestry & British Timber Vol. 36(9):16-18, 20, 22-23.