Advice
RHS Help & Advice
Horse chestnut bleeding canker
This is a newly identified and serious bacterial disease that causes bark death, canopy thinning and dieback and often complete death of the tree in certain species of horse chestnut.
Hosts
Horse chestnut (Aesculus species).
Symptoms
The disease starts with the development of patches on the trunk, which range from rusty-red to yellow-brown and black. A sticky liquid then oozes from these, tending to be dark and transparent in the spring, becoming rusty-coloured and cloudy as the season progresses. The inner bark is an orange-brown, often clearly mottled or striated. In advanced cases, cankers girdle the trunk, leading to crown thinning and dieback.
Biology
Caused by the bacterium Pseudomonas syringae pv. aesculi. Little is known about the infection process, but it is thought that it starts at wounds in the bark. Transmission is thought to occur by mechanical means.
Control
Trees will sometimes recover from the disease, so it is advisable to leave those with minor symptoms and monitor their progress. Horse chestnuts are prone to sudden limb drop when under stress, so prompt removal of dying branches and those with significant cankers is advisable. It is best to burn infected waste on site, to minimise pathogen spread. Tools and footware should also be sterilised after use. There are no chemicals to control the disease.
Further Information
Further information on the disease, with pictures of symptoms and details of the progress of current research can be found on the Forest Research website.