Bleeding canker is a disease that affects horse chestnut trees (Aesculus hippocastanum). The symptom of bleeding canker was first reported in Britain in the 1970s, although recognised in the USA much earlier in the 1930s. Pre-2000, symptoms of bleeding canker on horse chestnut were associated with two Phytophthora pathogens.
Today, the incidence of the disease within the UK has increased dramatically. In 2000 only four cases were reported but this rose to more than 110 reports in 2006. A systematic survey in 2007 across England, Scotland and Wales revealed around half the horse chestnut trees in Britain showed some symptoms of bleeding canker. However, the cause is now most often due to a bacterial pathogen, Pseudomonas syringae pv aesculi, and only very occasionally caused by Phytophthora.
This resource will help you to identify bleeding canker disease, understand some of the disease biology and select a suitable management strategy.
Details of the disease
- Trees of all ages are affected and can die
- Cankers and bark cracks on the stem
- Bleeding on the trunk and branches
Bleeding canker of horse chestnut is caused by at least two different pathogens. The symptoms of bleeding canker can also be seen on other tree species but are caused by different pathogens. For example, some root diseases can present with similar symptoms such as bleeding on the lower trunk and root flares.
Our research has shown that the increase in incidence in horse chestnut bleeding canker has been caused by the introduction of a previously unknown pathogen, Pseudomonas syringae pv aesculi.
Until 2000, bleeding canker thought to be caused by two fungal-like pathogens: Phytopthora cactorum and Phytophthora citricola (now called P. plurivora). Instead Pseudomonas syringae pv aesculi is now the most frequent cause of bleeding canker symptoms on horse chestnut throughout Britain.
Confirming the cause of symptoms of bleeding canker on horse chestnut is critical to any recommendations about effective management. Surveys are also recommended to assess the number and condition of affected trees.
There is no chemical treatment currently registered or approved for use in the UK to cure or arrest the development of bleeding canker caused by Pseudomonas syringae pv aesculi:
- If cankering lesions become extensive the entire trunk may be girdled and the tree will inevitably die and have to be removed.
- Consider removing major branches that are infected and show dieback. Recently-dead branches of horse chestnut may be susceptible to sudden fracture and drop as the wood dries out.
- Trees with bleeding cankers on the trunk can still have healthy-looking crowns and may not pose an immediate safety risk.
- Some trees may survive for many years as disease progression can be very slow or even show signs of recovery (vigorous callus development at the margins of cankers when bark has been killed by the disease).
- Removing affected trees unless they pose a safety hazard is unecessary. It will not prevent disease spread on a site where some trees already show symptoms. Also, significant numbers of trees do recover.
- Some trees are apparently resistant and never go on to develop symptoms despite exposure to the disease cause.
Find out more about specific recommendations on how to manage bleeding canker.
Forest Research scientists have identified the bacterium that is responsible for the increase in incidence of bleeding canker disease on horse chestnut. Researchers are now using molecular technology to characterise the biology of this pathogen.
Scientists are also exploring the impact that Phytophthora species have on the health of trees. Frequent symptoms associated with Phytophthora pathogens include bleeding canker on trunks and branches.
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