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Pseudomonas syringae pv. aesculi (Bleeding Canker of the Horse Chestnut)

Pseudomonas syringae pv. aesculi (Bleeding Canker of the Horse Chestnut)

There are around 2 million horse chestnuts in the UK.  Technically, it is not a true native tree although it has been here for centuries.

Bleeding canker was first reported in the UK in the 1970s and was originally associated with two low level Phytophthora pathogens (P. citricolaand P. cactorum), but a rapid increase in infection in 2002 resulted in the identification of Pseudomonas syringae pv. aesculi as the cause.

A Forestry Commission survey in 2007 confirmed that 49% of the UK’s horse chestnuts were infected with this bacterial disease which results in slow tree death.  Today it is estimated that the infection rate has increased to more than 70%. Most infected trees will die within 10-15 years and, in many places, damage in the form of felled horse chestnuts is already visible.  As in many cases of tree disease, the actual cause of death is the tree’s own defences which to prevent the spread of the bacteria, block the xylem with tyloses, effectively girdling and starving the tree.

The Forestry Commission website states that there is no chemical treatment available to cure or arrest the development of this disease.  Our lab results show that Pseudomonas syringae can be controlled and that implantation or injection treatment at the right stage can prevent tree death, making this a treatable disease, if caught in time.