What is ash dieback?
Ash dieback (Chalara fraxinea) is a serious airborne fungal disease caused by the organism Hymenoscyphus fraxineus, which primarily affects ash trees (Fraxinus species). The disease manifests through a range of symptoms, including wilting of leaves, blackened stems, and dieback of branches, ultimately leading to the death of infected trees. As they decline, the branches can become brittle and drop, or in some cases the main stem of the tree can become brittle and become a risk of total tree failure (falling).
Why is this a problem?
Ash dieback poses a significant and growing ecological and economic threat because ash trees are a vital component of many woodlands and urban landscapes in the UK. In Devon alone, it is estimated there are over 2 million ash trees (Source: Devon Wildlife Trust). Ash trees support diverse habitats, contribute to overall biodiversity, and play a crucial role in carbon sequestration, which helps combat climate change. The widespread mortality of ash trees has the potential to dramatically alter ecosystems and landscapes, reduce available wildlife habitat, and shelter for animals and humans.
What are the different stages of dieback?
There are different stages which advance as the fungal infection takes hold and spreads throughout the tree:
Initial Infection: During the first stage, small, dark lesions appear on the leaves and leaf stems of the ash tree. This is often most noticeable in the summer months, leading to early leaf loss.
Leaf Symptoms: As the disease progresses, leaves become increasingly discoloured, often turning yellow or brown. Necrotic lesions develop on the leaf margins, and overall defoliation occurs.
Branch Dieback: In this phase, branches start to show significant symptoms of dieback. Symptoms include wilting or dying leaves and the presence of dark marks on the bark, which indicates the movement of the fungus within the tree.
Crown Decline: The tree's crown begins to thin out further, showing extensive dieback. This decline may lead to significant reductions in height and overall vigour. Hyphal branching may be visible in the bark.
Bark Cracking: As the disease takes hold, the bark starts to crack, revealing dark streaks under the surface. This symptom is indicative of deeper invasive fungal activity affecting the tree's vascular system.
Tree Mortality: Ultimately, the affected tree may succumb to the disease, with complete death occurring several years after infection. In some cases, surviving trees may show partial resistance, while others become fully compromised.
Understanding these stages is essential for effective management and intervention in affected trees. Regular monitoring allows for timely actions to mitigate the spread of ash dieback across wider landscapes.
What can be done about infected trees?
To effectively manage trees that are affected by ash dieback, several proactive actions are necessary and should be undertaken promptly:
Immediate assessments should be conducted to determine the extent of the disease's impact and the viability of the affected trees. Some decline will be rapid, others will either take longer to decline, or may recover. A survey should be undertaken by a suitable arboricultural consultant (like us).
Infected trees should be monitored closely over time, and if they pose a risk to public safety due to their condition or are severely affected, they may need to be removed for safety reasons. If they are close to people and property in the event of a total failure, it is likely the tree will need to be felled. If the tree is in an areas where total failure wont cause harm to people or property, they can be left to decline and eventually become a value standing deadwood habitat.
Replanting with disease-resistant species or diversifying tree planting strategies is crucial for future resilience and the health of our woodlands.
Do you have an ash tree?
If you have an ash tree and are concerned about its health, get in contact for a survey. Now (March) is a good time to assess ash tree condition because the lack of leaves, enabling closer inspection of the volume of deadwood or lack of growth in the crown.
You can contact matt@generationarboriculture.co.uk or call 07846 510139, or fill out the contact form on our contact us page.