Ash Dieback. Did the disease really kill 90 percent of ash trees in Denmark? Is this really a good comparator for the UK and have 100,000 trees really been ‘felled’ in the UK?

A hub for crowdsourcing information and genomic resources for Ash Dieback.

On this website you’ll be able to get data to do your own analyses on ash and ash dieback.
You can see the results of other peoples work as soon as it is available and share your own discoveries in the same way.

You will always get full credit for your work and in doing so contribute to a real community effort.

[S]cientists are now saying it has been in the country for more than a decade.

Clive Brasier, a former Government adviser on forestry, said the fact that 121 of the infected sites are mature trees in the wider environment, rather than in nurseries or recent plantings, suggest that the disease has been spreading for years.

The disease will only spread the year after the tree has been infected. Prof Brasier, who continues to advise the Forestry Commission in his role as emeritus Mycologist at Forest Research, said foresters will have assumed trees showing signs of infection were suffering from other diseases or frost damage.

“It will not have been spotted because people would have thought it is wind, frost damage, other diseases or even squirrels.”


For foresters like Anders Grube, the disease is a management nightmare. Many of his ash trees have already been cut down – the timber worth a fraction of the price he was getting before the fungus arrived.

“It is a disaster. I am losing lots of trees and lots of money. In this forest I have lost about a million pounds,” he says.

“Before this disease we were getting double the money for ash we are getting now. I am lucky I can sell to China, but I am only getting half the price.”

Ash dieback also causes big problems for those who rely on a steady supply of ash wood.

As some ash species show very few symptoms after infection, they may act as undetected carriers.  There is evidence of low susceptibility to disease in some Asian ash trees (Drenkhan and Hanso, 2010). (Moderate confidence)

Common ash (Fraxinus excelsior) is the most severely affected species.  Young trees are particularly vulnerable to C. fraxinea and succumb to disease rapidly.  (Kowalski, 2006; Forest Research, 2012).  (High confidence)

There is no evidence that C. fraxinea can spread to tree species other than ash. (High confidence)

Infection is via spores from fruit bodies on leaf litter.  Spore production (in fruit bodies) occurs on infected fallen leaves and shoot material in the growing season after infection (High confidence)

C. fraxinea infection starts primarily on leaves, and is progressive over time, with dieback and stem lesions usually manifesting in the next growing season.  Leaf symptoms can be detected within two months of infection. (Moderate confidence)

C. fraxinea causes infection from June – October, mainly in July – August. (High confidence)

Spores are produced on Chalara fruit bodies formed on fallen leaves and shoots the year following infection. Natural spread is by wind-blown spores (ascospores). Wind-blown spores cause the disease to spread up to 20-30 km per year. Longer-distance spread occurs via infected plants or potentially via wood products. (High confidence on wind dispersal; Moderate confidence on untreated wood products)

There is low probability of dispersal on clothing and footwear or via animals and birds. (High confidence).

C. fraxinea is found in seeds (Cleary M., et al. 2012), and this is reflected in the legislation, which restricts the movement of plants and seeds. (High confidence)

There is a lower risk of C. fraxinea spreading over the winter because there is now a ban on ash plant and seed imports into the UK, restrictions on plant movements through Statutory Plant Health Notices, and spore production is not expected to resume until June 2013. (High confidence)

larger trees can survive infection for a considerable time and some might not die. (High confidence)

The impact of C. fraxinea infection depends on tree age, location, weather conditions and co-presence of honey fungus (Armillaria) or other secondary pathogenic / opportunistic organisms. Trees in forests are more susceptible because of the greater prevalence of honey fungus. Timber trees are generally felled before they are killed by honey fungus.

  • 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 more than 40 years old, there is no direct evidence of tree deaths just from C. fraxinea to date, but there is little comprehensive survey data from Europe on which to base firm conclusions.
    (Moderate confidence)