So you think you have a Diseased Tree – what to do.
Among the first symptoms that an ash tree might be infected is blackening and wilting of leaves and shoots in mid- to late summer (July to September). These months are the best time of year to survey ash trees for symptoms in the foliage. This is because once autumn begins in late September or October, the normal seasonal change in the colour of the leaves can be mistaken for symptoms of the disease.
Most infected leaves are shed prematurely by the tree, but in some cases the infection progresses from the leaves and into the twigs, branches and eventually the trunk, causing dark lesions, or cankers, to form in the bark. These often have a characteristic elongated-diamond shape.
Report a sighting
Management and Control
You are not legally required to take any particular action if you own infected ash trees, unless your country forestry or plant health authority serves you with a Statutory Plant Health Notice (SPHN) requiring action. This is unlikely.
With the exceptions of felling for public safety or timber production, Forest Research advises a general presumption against felling living ash trees, whether infected or not. This is because there is good evidence that a small proportion will be able to tolerate H. fraxineus infection. There is also the possibility that a proportion of ash trees can become diseased, but then recover to good health. These, too, would be valuable for research, although it is still too early to know whether there are such trees in the British ash population.
However, by keeping as many ash trees standing as possible, Forest Research can identify individuals which appear to survive exposure to the fungus and which can be used for breeding tolerant ash trees for the future.
That said, public safety must be the priority, so keep an eye on the trees’ safety as the disease progresses, and prune or fell them if they or their branches threaten to cause injury or damage. In particular, watch for basal lesions (lesions, or cankers, forming near the bottom of the trunk), which can weaken the trunk and make the tree more prone to falling.
There is no known cure, although some fungicides might be effective in suppressing the disease, enabling individual ash trees of particular value to be saved. These might include trees of high amenity, heritage or cultural value. However, such treatments often have to be re-applied periodically, perhaps every year, and can therefore be expensive.
- Ash dieback (Hymenoscyphus fraxineus)
- Interactive Map
- Pictures of Ash DieBack (Hymenoscyphus fraxineus)
- Tree Alert