What is it ?
It is a fungus which originated in Asia. It was introduction to Europe about 30 years ago and has devastated the European ash (Fraxinus excelsior) because our native ash species did not evolve with the fungus. This means it has no natural defence against it.
*Note it does not affect rowans also known as mountain Ash (Sorbus aucuparia)
What happens to the tree ?
The fungus overwinters in leaf litter on the ground then release spores into the surrounding atmosphere during the summer. They land on leaves, stick to and the fungus then grows inside the tree, eventually blocking its water transport systems, causing it to die.
These spores can be carried by the wind many miles away.
The tree can fight back, but year-on-year infections will eventually kill it. Young trees are more likely to die quicker than mature trees.
What does Ash Dieback Look Like?
There are several symptoms but they are not all always be present
- Lesions on the stems
- Browning of the leaves and early leaf fall
- Retaining their seeds or 'Keys' over the winter
- The foliage in the crown of the tree gradually thins as the disease progresses
There are 4 catergories which identify the level of disease in the tree. They are:
Category 1 (T1) - A healthy tree with a good healthy leaf coverage 100% - may be minor signs of disease eg early leaf fall, some leaf browning.
Category 2 (T2) - A tree starting to show signs of disease - 75% leaf coverage/crown density with some other indictors, some leaf browning, lesions or brown keys.
Category 3 (T3) - A tree which is clearly diseased - 50% leaf coverage/crown density. Tips of branches die back, brown keys evident and foliage becomes 'clumpy'.
Category 4 (T4) - A tree which is clearly in terminal decline 25% of less leaf coverage/crown density may have larger dead branches.
How to identify and ash tree and Ash Dieback [1MB]
