Deadly fungus will infect most ash trees in the south and east of England by 2018, government models suggest

The spread of a deadly fungus killing ash trees in the UK could affect up to three-quarters of the species in the worst-hit areas within just four years, according to government scientists.

Conservationists said such a rapid spread would be "devastating" to landscapes and have a "very real economic cost".

Chalara fraxinea, a fungus that was found in England in 2012 after being blown over the English channel or imported via nurseries, causes the crown of ash trees to blacken and wither, and can kill younger trees.

Ministers have admitted the spread of the disease cannot be stopped, and are resigned to mitigating the worst distribution and impact of the organism on the UK's estimated 80 million ash trees.

By 2018, more than 75% of ash in Kent will be infected by ash dieback, with a similar percentage of ash in Sussex affected, modelling published in the government's tree health management plan shows. Ash is the most abundant species in Kent, making up around a fifth of the county's trees.

Other counties in the east will be badly hit, it predicts, with around half of ash trees in Essex, Norfolk and Suffolk expected to be infected by 2018.

Austin Brady, director of conservation at the Woodland Trust, said: “If the predicted spread of ash dieback is accurate it would prove devastating to the landscapes of Kent and East Sussex in particular. This highlights the need to ensure that other species can fill the gaps and help restore lost tree cover. This will only happen in the long term if we ensure that risks to our remaining species are identified and minimised and we work to boost the natural resilience of our woods by improving their diversity.”

Nick Johannsen, director of the Kent Downs Area of Outstanding Natural Beauty, said:“Ash is a critical component of Kent’s land and townscape and already we have seen a major impact from ash dieback. The costs of the loss of many ash trees in the county will be many fold, our landscapes and townscapes will diminish and our wildlife will suffer, there will be a very real economic cost in making roads, railways and urban areas safe as trees succumb to primary and secondary infections over time."

Ash dieback distribution map. Photograph: /Defra

Ash makes up just under 5% of the UK's woodlands, and as well as being a vital part of the UK's ecosystem – 45 species are only found on the trees – it makes for valuable timber. It is estimated to be worth £72- £124m annually in social and environmental benefits and is famously good for burning, known in poems as a firewood fit for a queen.

The Department for Environment Food and Rural Affairs said that it had already agreed payments totalling £120,000 for the removal of young ash trees to be replanted with other species, a strategy it announced in March 2013 to tackle the disease's spread.

A spokesman for Defra said: "This projection is based on our current understanding of Charala. We are learning about this disease all the time, having invested £8million into research in tree and plant health. We are working to identify a strain of ash tree which is naturally resistant to Chalara, both through research projects and through the largest field trial of its kind with 155,000 trees planted in East Anglia. Our woodland changes all the time but these measures will help to ensure that ash continues to have a place in our forests."

The tree health plan said that while there was no known cure for Chalara fraxinea, the pathogen has been tested with 17 chemical treatments, four of which it proved highly sensitive to.



"Further research is under way to test the level of control that can be achieved using the most promising chemicals under field conditions," the plan said.

The report highlights other threats to Britain's woodlands, including a caterpillar that is toxic to humans and strips oak trees of their leaves.

The oak processionary moth, so-called because of the way the caterpillars march in procession, has taken hold across south west London and officials were so concerned by its spread to a wood in Berkshire that they sprayed the area with insecticide from a helicopter last year.

Spraying to limit the caterpillar's spread in London will continue this year, "to contain the outbreak in south-west London and seek to eradicate outbreaks where they occur outside the outlying sites of infestation."