Most Unwanted: Chalara dieback of Ash

How to identify Chalara dieback of Ash (Chalara fraxinea)


  • Leaves turn black and hang on twigs
  • Dark, diamond-shaped lesions form where twigs meet the main stem
  • It leads to death of twigs and branches.

Plants affected:

  • Ash trees
  • Common Ash (Fraxinus excelsior) is very susceptible and young trees are particularly vulnerable.

UK status and other information:

  • Currently it has a limited distribution in the UK
  • Chalara fraxinea emerged as an entirely new disease in Europe in the 1990s. It has already infected a large number of Ash trees across continental Europe, with a
    significant loss of trees anticipated in the next 20 years
  • It was first found in Britain in 2012
  • There is evidence that it has spread between countries via the plant trade and at present there is a ban on imports and movement of Ash in the UK.

Why will any findings be important?

  • We need to know about the distribution and extent of Chalara dieback of Ash
  • Knowing exactly where it is will help us to manage the spread of this disease.

Could be confused with:

Useful links:


Images: leaves © Andrej Kunca, diamond shape © Forestry Commission, death of branches © Iben Thomas