While there are many ailments and conditions that can have a serious impact on the health of a tree, Chalara dieback of ash is an extremely serious disease that can have fatal consequences. The disease is caused by a fungus which is known as Hymenoscyphus fraxineus (while previously being referred to as Chalara fraxinea,) and the symptoms of the disease lead to the loss of leaves and crown dieback.
Symptoms of Chalara dieback of ash
The initial symptom of Chalara comes with leaves looking as though they have wilted with the next step seeing a discolouration of the leaves. It is common for affected leaves to grow much darker in colour with affected autumn leaves looking dark brown or black as opposed to the yellow and greens that should be seen on these trees. In later stages, the stem will also appear discoloured which occurs as the fungus makes its way through to the stem. After this, there are often diamond shaped lesions (commonly black or purple in colour) caused by the fungus making its way through the tree to the main trunk.
Development of disease in Britain
The condition was first uncovered in Britain in February of 2012 and it was related to sites where there has been the introduction of saplings from nurseries over the past five years. This led to ash imports from European countries being banned and in October of 2012, the government announced that around 100,000 saplings and nursery trees had been destroyed in an attempt to quell the spread of the disease but it was dubbed “too little too late” by many specialists.
The serious nature of the disease can be seen in the fact that comparisons have been made with the 1960s and 70s outbreak of Dutch Elm disease. However, the real extent of the concern over this disease comes with the fact that estimates suggest between 90% and 99% of UK ash tree population, standing at 80 million, could be wiped out by the disease.
Even taking a more balanced approach to the disease, there is no denying that Chalara dieback of ash has been responsible for significant damage to Europe’s ash population. There are enough findings to indicate that young ash trees can be killed off in a short period of time although more mature trees show a greater level of resistance. However, even mature trees which are exposed to the condition for a lengthy period of time or which are weakened and then impacted by another pest are at risk.
The key steps taking place in the United Kingdom are focused on:
- Slowing down the rate at which the disease is spreading
- Assisting trees to develop resistance
- Improve awareness of the condition to ensure people are looking out for the symptoms
While there is no strategy that has been declared as wholly effective for containing this disease, it has been found that the removal of infected trees or areas can be counter-productive as this doesn’t affect the fungus growing or living on the floor of the forest and it can also lead to many resistant trees being destroyed.
One step that is being encouraged, which is where calling on the services of an experienced tree surgeon can help, is to take branches from trees with a strong level of resistance and then grafting them to the rootstock in order to produce seeds that will hopefully be resistant to the disease. Early diagnosis and swift action has a big role to play in preserving the future of ash trees in Britain.