As many as two million conker trees in the UK could become a thing of the past over the next 15 years due to disease and an invasive moth.
The leaf-mining moth was found in Europe in 1985, spread rapidly through the continent and was found in southern England around 2002.
The moth’s caterpillars eat the tree’s leaves from the inside, turning the leaves brown and forcing them to drop in the summer before the conkers have fully grown.
Councils are also removing many horse chestnut trees to prevent people being hit by diseased branches when they fall.
The trees are no longer planted because they only last up to five years before they are killed.
The moth may also be responsible for bleeding canker, a fungal disease which can kill trees.
A Forestry Commission survey in 2007 found more than 70% of trees in some parts of England had the disease, with 36% in Wales and 42% in Scotland showing some symptoms.
The commission estimates around three-quarters of the country’s horse chestnut trees are in residential areas and parks, with the rest in woodland.
Professor Robert Jackson from the University of Reading said: “We have a major disease epidemic (bleeding canker) and pest (leaf miner) sweeping through the UK population of trees.
“The canker kills the tree whereas the pest seems to be reducing their vigour (wearing down their health).”
Professor Jackson added: “Most plant populations have some resistant individuals whose immune system can stop the infection, so we might see some trees survive, especially in woodlands.
“But at the moment the picture looks pretty bleak.
“Really we need to assess the population to see how resilient it is over time to see if it can survive.”
St John Burkett, one of the organisers of the World Conker Championships, has said: “It’s a bit of a concern but I think one of the biggest concerns is the human reaction to it.
“We’re quite keen to cut the trees down because they represent a bit of a danger to people with branches dropping off once the trees become ill.”
He added: “The problem is it’s not just the canker – a fungal disease – which is killing the trees but it’s the leaf miner.
“Because it’s a stranger to the country, none of the birds are eating the larvae and it can just lay as many eggs as it wants.”