Guide: What is 'ash dieback' disease and why is it threatening UK trees?

  • 29 October 2012
'Ash dieback' disease Image copyright forestry commission

A killer tree disease called 'Ash dieback' (or Chalara dieback) is threatening to wipe out thousands of the UK's ash trees but what is it?

It was recorded for the first time in the UK in October 2012 but here's our guide to why it's so deadly for trees.

What it does

Ash dieback does not affect humans but it does have a devastating impact on ash trees, one of the most popular species in the country.

It's caused by a fungus called Chalara fraxinea which kills the trees leaves and crown, or outer edge. In worst cases, it can lead to the tree completely dying.

It can affect a wide range of ash trees, including those in forests and cities, and even young trees in nurseries.

It's thought 'ash dieback' can be spread by infected wood moving around to different places.

Other possible ways of the tree infection spreading include rain 'splashing' the disease spores from one tree to the next, and insects transporting the disease.

'Ash dieback' has been found across much of mainland Europe. In Denmark, it's infected 90% of ash trees.