Millions of conker trees face being wiped out by deadly new disease

Tree experts believe bleeding canker disease has affected up to one million "conker trees", far more than anyone previously realised.

Thousands of trees have already been felled after succumbing to the bacteria, which first appeared in the UK a few years ago.

While the disease poses no threat to people, there are concerns that it could be one of the biggest threats since Dutch elm disease wiped out more than 25 million trees in the 1980s.

The condition is caused by a bacterium Pseudomonas syringae which appeared in Britain at the start of the decade. It has also been found in Germany and the Netherlands.

The bacterium causes bleeding cankers - "running sores" on trunks and branches - areas of dying bark that ooze liquid.

Until the bacterium arrived in Britain, bleeding canker was thought to be caused by fungus-like organisms.

Some trees become so weak they die, or have to be chopped down.

The Forestry Commission survey of 2,600 trees across Britain found that 49 per cent showed symptoms of bleeding canker.

Previously, tree experts believed only five per cent of horse chestnuts were infected.

The condition is most common in the South East, where around 70 per cent of trees showed symptoms. But even in the least affected parts of Britain, a third of horse chestnuts are suffering.

Roddie Burgess, head of plant health at the Forestry Commission, said little was known about how the disease spreads, and how it reached the UK.

"Horse chestnuts are a much-loved feature of the British landscape and we want to be able to offer manage advice to tree owners to help them minimise the impact of this condition," he said.

"We also need to learn as much as we can about the extent of the risk to horse chestnut and, if any, to other tree species."

The survey, carried out last summer, found that 54 per cent of urban horse chestnut showed symptoms of infection, while 44 per cent of rural trees were affected.

There are thought to be around one to two million horse chestnuts in Britain. The bacteria was first detected in the leaves of the Indian horse chestnut - a native of north west Himalayan region of the Indian sub--continent.

It is likely to have been carried to Britain on trees imported for planting.

There is no chemical treatment for the disease and some trees can recover from infection.

A spokesman for the Forestry Commission said the future for horse chestnut trees in Britain was unclear.

"We know that some trees survive bleeding canker, some die and some have to be felled for public safety reasons when the condition weakens the trunk or a branch to a point where it is in danger of falling," he said.

"There is also anecdotal evidence of uninfected trees being found very close tot trees that have been heavily infected for some time, suggesting that some horse chestnut trees might have a genetically inherited ability to resist the pathogens that cause bleeding canker."

The Commission added that the disease was very different from Dutch elm disease.

Because there were only one to two million horse chestnuts -compared to the tens of millions of Dutch elms - the disease would find it harder to spread and so as unlikely to have the same devastating impact on the countryside.