Horse chestnut bleeding canker (Pseudomonas syringae pv. aesculi)

What does horse chestnut bleeding canker look like?

Trees of all ages can be affected by horse chestnut bleeding canker. Some infections can last for years with little impact on the crown, while some spread rapidly and cause crown thinning, die-back, and sometimes death of part of or even the whole tree.

Symptoms include:

• Cracks in the bark which ooze dark or reddish-brown sticky liquid. These can dry out in winter, leaving a rusty-brown or black deposit.
• Discoloured wood under the bark. Healthy wood is a white or pinkish colour while an infected tree will have patches of brown or purple discolouration.
• On older cankers, the dead bark might fall away to expose the wood.

What is horse chestnut bleeding canker?

Horse chestnut bleeding canker is a bacterial pathogen.

The bacteria multiply within the water transport systems of the tree just under the bark, eventually blocking them. This causes the tree to die because it can no longer take up water.

How did horse chestnut bleeding canker get here and what impact will it have?

We don’t know how horse chestnut bleeding canker got to the UK. It was first recorded in the 1970s but was relatively uncommon until the mid-2000s.

The severity of infection can vary tree to tree. Some can withstand years of infection while others can die within a few years. The last survey for the disease was undertaken in 2007 and it found that 36% of the horse chestnut trees surveyed in Wales and 76% of the trees surveyed in South East England showed symptoms. The impact therefore could be significant with the loss of many mature horse chestnut trees.

What are we doing about it?

To combat pests and diseases like horse chestnut bleeding canker we have:

• Developed a UK and Ireland Sourced and Grown assurance scheme to make sure that all the trees we plant and sell are produced in the UK.
• Lobbied the government to improve biosecurity at border points to stop new pests and diseases entering the UK.
• Partnered with Observatree, a tree health citizen science project which trains volunteers to spot pests and diseases, thereby helping tree health authorities identify and manage outbreaks early.

What to do if you spot horse chestnut bleeding canker

If you think you’ve spotted the signs and symptoms of horse chestnut bleeding canker, please report it to the plant health authorities via TreeAlert if you are in Britain and TreeCheck if you are in Northern Ireland.