Threats to our horse-chestnut trees

Our horse-chestnut trees are facing a range of different threats. The most striking is the damage caused by the horse-chestnut leaf-miner.

The leaf-mining moth


Damage caused by the leaf-mining moth.

What is it? A tiny little moth (it's scientiifc name is Cameraria ohridella), which has caterpillars that mine the inside of the horse-chestnut leaves.

What damage does it do? Each caterpillar living inside the leaf produces a blotch about the size of a ballpoint pen lid. Blotches are initially pale, but turn brown. Get enough leaf mines and the tree can turn so brown that it looks like autumn has come early.

How serious is it? It does not kill the tree. There is mixed evidence of the effect it has on the trees, but it does reduce the photosynthetic capacity of the tree - meaning the tree produces less food for itself.

How long has it been attacking our conker trees? It has only been in Britain since 2002. It spread from London at a rate of about 30km per year and is now found across most of England and Wales - but not any further than Newcastle.

Don't confuse it with the leaf blotch fungus. Find out how to tell the two apart.

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The leaf blotch fungus


Damage caused by the leaf-blotch fungus

What is it? A fungus (it's scientific name isĀ Guignardia aesculi) that lives inside the leaf - the only sign of the fungus is the damage it does to the leaves.

What damage does it do? It produces brown blotches on the leaf. The blotches are irregularly shaped and have a yellow ring around their edge.

How serious is it? Not at all serious, it is just a little unsightly. Damage happens late in the summer. It is especially prevalent in damper climates in the west of Britain.

How long has it been attacking our conker trees? It was accidentally introduced from North America about a century ago.

Don't confuse it with the leaf blotch fungus. Find out how to tell the two apart.

Find out more


Bleeding canker


'Bleeding' from the trunk is the most
obvious symptom of bleeding canker

What is it? Many different organisms cause symptoms called bleeding canker in trees. The current disease in horse-chestnuts is caused by a bacterium called Pseudomonas syringae pv aesculi.

What damage does it do? To put it simply it clogs up the tree's veins. The most obvious symptom is weeping wounds from the trunk of the tree and rust-coloured stains on the bark.

How serious is it? It is very serious. It is likely to cause the ultimate death of the tree, although many individual trees can cope with the bleeding canker for a long time. In serious cases it can cause tree boughs to die and drop without warning. It is worth ensuring that

How long has it been attacking our conker trees? Although different types of bleeding canker have been attacking horse-chestnuts for a long time, this current epidemic has been spreading since about 2000 (which is about the time the leaf-miner arrived).

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