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Ash dieback disease

Ash dieback is a highly destructive disease of ash trees (Fraxinus¬†species), especially the United Kingdom’s native ash species, (Fraxinus excelsior). It is caused by a fungus named¬†Hymenoscyphus fraxineus, the disease is also known as chalara, ash dieback and chalara dieback of ash.

Spread in the UK

The disease is of eastern Asian origin. Its introduction to Europe about 30 years ago has devastated the European ash and because our native ash species have not evolved with the fungus, they have no natural defence against it.

Ash dieback has spread ferociously throughout Europe due to airborne spores and trade in ash saplings. When the disease was confirmed in the UK, it was eventually shown to have been imported on saplings which were then planted at multiple sites across the country. The disease is now found across the UK including in South Gloucestershire, there is no cure and very few trees are showing signs of long term resistance, therefore control of the spread is no longer considered viable.

It is expected that less than five per cent of ash trees will prove to be resistant to this disease.

The symptoms

The most obvious signs that a tree is infected with the disease are:

  • dead leaves being held on the tree (not to be confused with hanging seeds or keys which is normal)
  • infection spreading from leaf tip along midrib and into stalk
  • dieback of the crown so that the ends of branches are visibly dead.

Management of infected ash trees

Experience in continental Europe indicates that the disease can kill young and coppiced ash trees quite quickly. However, older trees can resist the disease for some time until prolonged exposure, or another pest or pathogen, such as Armillaria (honey fungus), attacks them in their weakened state eventually causing them to succumb.

Dealing with infected trees can be problematic as many argue that felling live ash trees should be avoided due to the impact on amenity and biodiversity. However, this needs to be measured against the risk of falling branches or whole trees, as the structural integrity of infected trees rapidly declines, especially in public areas.

From March 2020, we are rolling out a programme to remove infected ash trees. Due to the number of trees which need to be felled, we have implemented a priority schedule and will first fell infected trees within falling distance of our A road network. Following this, we will remove trees near B roads, in schools and other public open spaces.

In addition to the management or removal of infected ash trees, council officers and members are currently working on funding arrangements to cover the cost of replacing our valuable tree stock lost to the condition. It may not always be practical to plant a new tree in the exact location of those removed but an equivalent number will be planted elsewhere win South Gloucestershire.

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