On 2 April 2008 we published a report on a survey into the incidence of horse chestnut trees (Aesculus hippocastanum) displaying symptoms of a new disease in Great Britain, referred to as Horse Chestnut Bleeding Canker and caused by the bacterium Pseudomonas syringae pathovar aesculi.
Horse chestnut trees had for many years been affected by two water mould organisms, Phytophthora citricola and P. cactorum, which also cause bleeding cankers, but at a low level which had not given cause for concern.
However, in the first few years of the 21st century Forest Research scientists noticed that many specimens sampled did not reveal presence of either Phytophthora. They subsequently isolated a bacterium, Pseudomonas syringae pv. aesculi, which originates in the Himalayas.
A Great Britain-wide survey in 2007 to better understand the incidence and distribution of this bacterium found 49 per cent of trees surveyed showed symptoms which indicated or might have indicated infection by it: regional averages ranged from 36 per cent in Wales to 76 per cent in South-East England.
The information obtained from the survey provided a scientifically sound picture of the extent of the symptoms of the problem, and a basis for decisions about further research to learn more about the the disease with a view to developing appropriate management advice for tree owners.
Forest Research scientists are also conducting a long-term study to determine whether there are any interactions between P. syringae pv. aesculi and the insect pest Horse chestnut leaf miner, including whether one influences the extent of the other, and how they affect the health of affected trees. A paper reporting the results of the first 10 years of the study was published in the journal Agricultural and Forest Entomology.