Information about Covid19:
Please read our information on how we are supporting residents and businesses, as well as information on affected services.

Disease Identification

The First Signs of Ash Dieback 

The leaves will start to develop dark patches during the summer months (July to September). These leaves will wilt and begin to discolour to black.  Often you may notice dead and blackened leaves hanging amongst live foliage. The bark of live shoots and twigs will become discoloured and darkened, often with a purplish tinge

Continue reading

The disease will cause diamond shaped lesions where older twigs and branches join the stem or trunk. Lesions are areas of discoloured, sunken and dead bark. These lesions can eventually wrap around and kill the affected branch, stem or trunk. Often trees will respond by producing a growth of new shoots and leaves beneath the lesion.

Please note: care needs to be taken when identifying the disease, as other diseases and conditions may cause similar symptoms. 

The Forestry Commission, Woodland Trust, Arboricultural Association and the Tree Council have all produced online guides to aid identification of the disease.  We have found these two guidance documents particularly useful:

This video about how to identify ash dieback in the field from the Forestry Commission is also really helpful.

All ages of trees can be affected. Younger trees can decline and die in one or two growing seasons.  Mature trees have greater resilience and may decline over numerous growing seasons. 

  As the disease progresses the leaf canopy will decline. Leaf cover will become sparse. Dead twigs and small branches will become visible    at the edge of the canopy. Lesions will start to become increasingly obvious upon larger branches and stems. In later growing seasons larger dead branches and dead stems will become visible. You will often see a flush of new growth below the dead stem. Mature trees may survive for many years with a smaller canopy. As branches and stems die back there will be a greater possibility of falling deadwood. The longer the deadwood is present, the greater the chances of it failing. This presents an increasing risk to the public and property. 

The loss of the leaf canopy places trees under stress. This can make them more vulnerable to other diseases and decay fungus. It is often fungus and other diseases in combination with ash dieback that will cause the death of more mature trees.

Trees can also be infected at the base of their trunk when they are surrounded by many diseased trees and diseased leaf litter. Lesions will be visible at the base but there may be no obvious signs of infection in the leaf canopy. When combined with the effects of other decay fungi, the tree can become unstable over time, leading to tree failure. (See Responsibilities - Landowners and Cornwall Council). 

Look out for sunken and dark lesions on the branches and trunk, and young shoots or twigs with a dark purplish tinge. Also, dead twigs and branches in the upper crown of the tree. Please note it is advisable to wait until the tree has come back into leaf to confirm the presence of the disease. This is because some similar symptoms can be caused by other factors, such as insect attack, other diseases or old age.

Ash dieback is caused by a vascular wilt fungus. This is a fungus that affects the water transport system of trees, which is just beneath the bark. 

The fungus (formally known as Chalara fraxinea) produces small white mushroom-like growths (Hymenoscyphus pseudofraxineus) between July and October. The fungus develops upon leaf stalks found within the leaf litter from the previous autumn's leaf fall. These release numerous spores into the air. Winds can then disperse the spores many miles from the original site. Trees need a high ‘dose’ of spores to become infected. This means that isolated ash trees are often slower to be affected by the disease.

The spores land on the leaves, which are then penetrated by the fungus and the disease spreads through the stems. Ash trees that are surrounded by diseased trees and diseased leaf litter can also become infected at the base of the tree. Please note that there is a very low likelihood of spread by clothing or from animals or birds.  As the disease is spread by winds it is not possible to protect trees from the fungus.

This photo shows the fruiting bodies (mushroom like growths) of ash dieback upon a leaf stem (photo: Forest Research).

The disease originated within Asia, and both the Manchurian ash (Fraxinus mandschurica) and Chinese ash (Fraxinus chinensis)  have resistance to the disease. Our native ash (Fraxinus excelsior) has not had the benefit of evolving with the fungus and so has very little or no resistance to it.  The disease is also known to affect other ash species. These include Manna ash (Fraxinus ornus), Black ash (Fraxinus nigra), Green and Red ash (Fraxinus pennsylvanica). 

There is a very low likelihood of other trees or plant species being affected and there is no evidence of harm to animals or wildlife apart from the considerable loss of habitat.