Confirmed cases of the deadly tree disease ash dieback are now so widespread that controlling the illness without a cure will pose "long term problems", the environment secretary warns.

Confirmed cases of the deadly tree disease ash dieback are now so widespread they are beyond containment, experts warn (Reuters)

Owen Paterson conceded that earlier estimates that 80m ash trees may be lost to the illness were likely to be an "underestimate" and that we were "at risk of losing a significant number of ash trees".

A survey of 2,500 blocks of land by plant health experts has established that the disease has been confirmed in 115 sites across Britain, from woodlands in the south east, including Sussex and Berkshire, to Yorkshire and Northumberland in the north. It had already been identified in countryside in Norfolk and Suffolk.

Speaking after a tree health summit involving businesses, charities and woodlands organisations, Mr Paterson said: "This is a serious long term problem if we have an airborne disease which has come in, for which we have no cure.

"I don't begin to underestimate the difficulties of this problem. It will be long and hard and will present a real problem for years, but we can over come it if we work together."

The department for food and rural affairs (Defra) insisted that the discovery of the disease chalara ash dieback, does not mean that it is spreading rapidly, and that instead, it is likely it has been present in these areas for a number of years.

But experts have warned that it has now taken hold so extensively that there is little that can be done to combat it. Defra added that it is unlikely that all cases of the disease have yet been identified, and "it is likely that more cases will emerge as checks continue".

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Commentary from Science Editor Tom Clarke:

The red dots on today's forestry commission map show cases of Chalara fraxinea in the wild now outnumber cases found in nurseries and newly planted areas. What's more, they cluster along the east coast, rather than clump around the imported disease.

The take-home message seems to be is that the disease probably made its own way here on the wind - and could have been here for some time. If the government had immediately banned imports the disease would always have got here - or been here already.

However, some of the criticism levelled at the government over the slow action on ash dieback is justified. Despite awareness of the disease since 2009, the movement of ash trees in and out of Britain continued. Today's new figures reflect how important the trade in trees has been in bringing the disease to our shores - its been found in 15 nurseries and 39 planting sites.

So it's probably too late for us to save our ash trees. Instead we will have to rely on the species' own natural resistance to do that. But this latest crisis could well force much needed change that tree experts in Britain have been calling for for a long time. There is a woeful lack of biosecurity when it comes to the trade in plants. Millions of plants and thousands of tonnes of soil come into Britain each year. Many other familiar tree species such as oak, larch, plane and scotts pine remain under threat. More funding and profile is needed for plant diseases.

But it's also time the value of our woods was recognised, not just for walking the dog, but as a breeding stock from which to grow and maintain a more robust domestic forest industry. That would benefit our forests, and our economy.

The warnings were made after the summit involving charities, businesses and woodlands organsations, and was chaired by the environment secretary, Owen Paterson.

However, despite a second Cobra meeting scheduled to discuss the crisis on Friday, the government has not yet given any indication of what it intends to do to treat or combat the illness.

The government has faced criticism for apparent inaction, with the disease first confirmed in February this year. The Horticultural Trades' Association urged the Forestry Commission to ban imports of ash trees from Europe in 2009 after seeing that the illness was widespread in Norwegian nurseries.

Ash dieback, which is caused by the fungus Chalara fraxinea, causes leaf loss and crown dieback in affected trees and may lead to tree death.

However confusion over the exact cause of the illness, and problems with identifying it, has delayed any potential action.

Imports have already been banned, and some 100,000 trees culled.

Ash dieback death rate
•Trees under 10 years of age are likely to die from C. fraxinea in 2-10 years.
•Trees under 40 years old will die in 3-5 years if also infected with honey fungus, and likely more rapidly if the tree is already debilitated.
•For mature trees over 40 years, there is no direct evidence of tree deaths just from C. fraxinea to date. But comprehensive survey data from Europe on this is scant.

The illness has already devastated 90 per cent of Denmark's trees, and it is feared that the effect of the illness in the UK could be as disastrous as Dutch elm disease, which wiped out 25m of Britain's 30m elm trees after it arrived from north America in the 1920s.

Although there is no evidence that it can spread to other tree species, or that it is harmful to the health of people or animals, the illness could completely alter the look of British woodland landscapes if it continues.

Defra has pointed to scientific advice from Norway which suggests the disease progresses some 30km a year. They will continue to survey land for further traces of the illness.

Martin Ward, chief plant health office, said: "We have thrown all possible resources at this surveying exercise which has given us a much clearer picture of the distribution of the disease to inform our evidence base.

"The science on Chalara is still emerging and the more evidence we have, the greater our knowledge and understanding of this disease and the better we are able to tackle it.

"Together we've surveyed over 92 per cent of England and all of Scotland and Wales so far - a tremendous achievement, especially in such a short time, which shows our combined determination to deal with Chalara."

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