What is the problem?

Our conker trees are under attack!

Horse-chestnut ('conker') trees have been part of our landscape for only a few hundred years [find out more]. They were planted in parks because they are such beautiful trees - wonderfully shapely, producing white 'candles' of flowers in spring and, of course, conkers in the autumn. But our conker trees have recently come under attack from pests and diseases.

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.

Find out more

The leaf blotch fungus

Damage caused by the leaf-blotch fungus

What is it? A fungus (it's scientific name is 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

Trunk wounds are 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).




Conker Tree Science is a 'citizen science' project in which anyone can get involved in scientific research about the horse-chestnut leaf-miner moth.

The main project ran for four years from 2010 to 2013. It was hypothesis-led, which means that the records that people submitted directly contributed to answering some questions about the leaf-miner moth. The first paper with thes results was published in the scientific journal PLOS ONE in 2014. One of the aims of the paper was to show that people could collect scientifically-valuable data.

From 2014 onwards we have changed the project. The aim of the project for now is to undertake longer-term monitoring of records of damage caused by the leaf-miner moth and also the leaf-blotch fungus.