Ash Dieback – References & Background

External Site References

BBC News Archive 8th March 2013 – Inside lab unravelling genetic code of deadly tree fungus
BBC News Archive 8th March 2013 – Ash fungus genetic code unravelled 8th March 2013 – Woodland devastated by ash dieback could be restored by finding resistant trees
Forestry Commission – Ash Dieback Symptoms Leaflet
Woodland Trust / – Threats to our trees
Smiths Gore – Ash Dieback Article – Fight to save a third of Britains trees from killer fungus – Ash Dieback – How to spot Chalara fraxinea in your garden – Ash Dieback – One of ten epidemic tree pests and diseases.html – Ash Dieback mistaken for squirrel damage – Must we ban the privet hedge to save the ash

Ash Dieback, A Background piece submitted by our Chairman, Roland Fox

Although European ash (Fraxinus excelsior) is not particularly common in Crinnis Wood, it totals around a fifth of all trees in the whole of the UK and is often the most common tree on limestone soils.

Ash Dieback is caused by a fungus that can be deadly to ash trees. It was first diagnosed twenty years ago in an area of Poland. Since then it has spread to ash trees in over 20 European countries, especially devastating around the Baltic. Elsewhere the impact has been varied with some ashes surviving. It spreads by wind and its spores are quite capable of being blown to the British Isles. Also it could have been brought here on infected imported trees, migrating birds, vehicles and people. Whatever the route, it has now been found on many sites throughout Britain and Ireland.
The disease was detected first in several English nurseries where the outbreaks were traced to trees and seeds that had been imported from countries already affected. The Horticultural Trades Association (HTA) in Reading, which represents British suppliers had already warned the government in 2009 that the disease was rife in Danish nurseries and could easily reach the UK but this warning was ignored and over 100,000 nursery trees and saplings have since been destroyed. However since then the disease has also been
detected on mature wild ash trees, it probable that the fungus spread here naturally when spores landed on leaves, germinated and invaded their tissue before moving into the leaf stalks. From these the fungus could spread into the tree trunk and once there block off its water supply thus killing the tree.

However the fungus does not spread from infected trees themselves, but from infected leaves shed in the autumn. The fungus then grows on the leaves and leaf stalks as they decay to produces abundant spores in
summer which spread to uninfected ash trees, completing the life cycle. The fungal species exists in two forms, Chalara fraxinea that reproduces itself asexually, and one called Hymenoscyphus pseudoalbidus that multiplies sexually by producing spores.

Most likely the fungus originally came to Poland from Asia, either via the wind or accidentally brought in on imported ash trees. There is circumstantial evidence as Asian ash trees like the Fraxinus ornus trees
(some are growing locally in some Wheal Regent Park gardens and the Tesco car park) are immune to the disease. Alternatively H. pseudoalbidus could have evolved from a harmless European relative. It is also feasible climate change has made European ashes more vulnerable to a pathogen that was already here. In Lithuania, where 99 per cent of the original ash population died out, the offspring of the survivors are proving resistant.
In the meantime, the UK government has banned any further imports of ash trees and ordered a survey to establish how far the disease may have spread. It is possible that in the whole of Europe, ash tree populations could be reduced to less than 10 per cent what they were originally

Ash Dieback fungus is not the first introduced plant disease problem, nor will it be the last. It is unfortunately true that imported plants are often the main source of deadly tree diseases. The US Department of Agriculture have shown that the fivefold increase in importation of live plants in the US
over the past half-century,was responsible for 70 per cent of the worst non-native pathogens afflicting US forests. Nursery plants from Asia are the source of California’s sudden oak death which is caused by Phytophthora ramorum which also infected the feral Rhododendron ponticum that had to be removed from Crinnis Wood and neighbouring Council land. Another example is chestnut blight that spread to the US on imported Japanese chestnut trees in the late 19th century. Dutch elm disease that wiped out Britain’s elms is the result of hybridisation between two strains of the disease-causing fungi. English elms are a clone that was propagated by cuttings. Fortunately ash is genetically diverse so some trees are resistant
to the fungus implying that the outbreak may not prove as catastrophic as Dutch elm disease.

If you see or suspect any of the symptoms illustrated in the links provided, please let us know immediately.