During the past week national and local news has reported the outbreak of a disease affecting ash trees, Chalara Fraxinea, or Chalara Dieback, has been detected in South East England.

What is Chalara Dieback?

Chalara Dieback is a fungal disease that causes leaf loss and crown dieback in affected trees, and can lead to the death of the tree, especially in young saplings. The disease is found in many countries across continental Europe and has resulted in the death of many ash trees – it has killed up to 90% of the ash trees in Denmark alone. Until earlier this year it had not been detected in the UK. Since February it has been detected in ash saplings imported from nurseries in Europe. Last week it was found in recently planted woodland in East Anglia which had no association with sapling trees from imported stocks. It was also found earlier this month in Co. Leitrim in the Republic of Ireland. To date it has not been detected in Northern Ireland.

If allowed to become widespread, has the potential to wipe out the ash tree population in the same way Dutch Elm Disease almost wiped out the elm tree population back in the 1970s. At this stage it is thought the disease is spread by airborne spores.

Government Response

The Department of the Environment, Food and Rural Affairs (DEFRA) has banned the import of ash trees into the UK, with the NI Executive and the Irish Government bringing in similar bans. All infected trees are being destroyed. They have also advised that anyone visiting woodland should clean their boot/shoes of mud to prevent any potential spread.

In Northern Ireland the Department of Agriculture and Rural Development (DARD) has commenced a programme of monitoring recently planted ash woodland to assess whether the disease is present in Northern Ireland. They are urging everyone engaged in the plant/forestry industry to be vigilant for, and to report, any signs of the disease – this includes NIE.

Symptoms to Look For

Chalara Dieback can be visible on leaves, shoots and branches of affected trees. Leaves can suffer from wilting and black-brownish discoloration (1) and dieback of shoots and twigs is very characteristic. Small lesions can appear on the bark of stems and enlarge over time (2). These can cause wilting and dieback of shoots and branches, particularly in the upper crown. Underneath the bark lesions the wood has a brownish to grey discoloration (3) which often extends beyond the site of the lesion.

Trees with withered tops and shoots are also very characteristic. Heavily affected trees have extensive crown loss, shoot, twig and branch dieback (4). It is also important to remember that some of these symptoms can stem from causes other than Chalara Dieback, such as root disturbance, bugs & insect larvae, fungus or frost damage.