Horse Chestnut Bleeding Canker Or Brown Leaves

What's happening?

The RHS says horse chestnut leaf miner causes white or brown blotches that by August can cover most of the leaf and give the impression the tree is dying, although it will survive, and that the tree appears to tolerate it so control is not necessary or practical. Forest Research says bleeding canker is a disease of European horse chestnut in Great Britain characterised by lesions on the stems and branches that ooze dark fluid, in most cases since 2000 caused by the bacterium Pseudomonas syringae pv. aesculi. It says there is no chemical treatment registered or approved in the UK, that some trees recover and some are resistant, and that similar bleeding can have other causes such as root diseases, so confirming the cause is critical.

What usually causes it?

• Horse chestnut leaf miner, which causes brown blotches on the leaves by late summer
• Bleeding canker caused by the bacterium Pseudomonas syringae pv. aesculi, with lesions that ooze dark fluid
• A root disease, which can cause similar bleeding on the lower trunk and root flares
• More than one problem at once: Forest Research says leaf miner might exacerbate decline triggered by other threats
• Drought or flood damage to leaves

Is it dangerous?

Medium. Forest Research says recently dead branches of horse chestnut can be susceptible to sudden fracture and drop as the wood dries out, and that for public and property safety you may consider removing major infected branches that show dieback. It also says trees with trunk cankers can have healthy-looking crowns and might not pose an immediate safety risk. Keep people away from a tree with dead branches and ask a tree surgeon to assess it.

Can I fix it myself?

Look at the symptoms. Brown blotches between the veins that appear from summer are leaf miner and need no action, according to the RHS. Dark, gummy fluid and cracked bark on the trunk or branches point to bleeding canker: do not apply treatments, because Forest Research says none is approved in the UK. Ask a tree surgeon or arboriculturist to confirm the cause and check the safety of dead branches. Forest Research says there is no need to report suspected bleeding canker to them.

When should you call a tree surgeon?

Call a tree surgeon when there is fluid oozing from the trunk, dieback or dead branches, or when the tree is near a house, road or path. Forest Research says confirming the cause is critical to management, and surveys help assess affected trees.

What will the tree surgeon actually do?

• Examine the trunk, branches and root flares and confirm whether it is bleeding canker, leaf miner or a root disease
• Assess the safety of dead and dying branches
• Remove major infected dead branches where they are a risk
• Advise on monitoring a tree that has cankers but a healthy crown
• Write a condition report for the owner, the council or an insurer

Who fixes this

• Tree survey and report
• Deadwood removal

Questions people ask

Sources & References

1. Forest Research: bleeding canker of horse chestnut
2. Forest Research: horse chestnut leaf miner
3. RHS: horse chestnut leaf-mining moth