Forestry Commission map shows incidence and distribution of the disease
Figures released this month by the Forestry Commission show more than 1,100 reported cases of Chalara dieback of ash in Britain just three years after Defra first discovered the disease in a Buckinghamshire nursery.
Chalara dieback of ash, also known as Chalara or ash dieback, is a disease of ash trees caused by the fungus Hymenoscyphus fraxineus. It causes leaf loss, crown dieback and bark lesions in affected trees.
Once a tree is infected the disease is usually fatal, either directly, or indirectly by weakening the tree to the point where it succumbs more readily to attacks by other pests or pathogens, especially Armillaria fungi, or honey fungus.
Chalara dieback of ash has the potential to cause significant damage to the UK’s ash population, says the Forestry Commission, and it has already caused widespread damage to ash populations in continental Europe, ‘where experience indicates that it can kill young ash trees quite quickly’. Older trees, on the other hand, ‘can resist it for some time until prolonged exposure, or another pest or pathogen attacking them in their weakened state, eventually causes them to succumb’.
The best hope for the long-term future of Britain's ash trees, it adds, lies in identifying the genetic factors which enable some ash trees to tolerate or resist infection, and using these to breed new generations of tolerant ash trees for the future. ‘Government scientists, including our Forest Research agency, are working hard on this in partnership with a range of other respected scientific research institutions.’
The Landscape Institute Biosecurity Group is operating as part of the LI Technical Committee to ensure that the landscape profession remains informed of the significance of numerous plant health issues in particular ash dieback says chair Roger Kent.
The group recently held a review of its key objectives, he adds, ‘and confirmed firstly to continue to engage as members of the government’s Tree Health Policy Group with DEFRA, FERA, the FC and other stakeholders to influence them to take more account of the loss of non woodland trees’.
The LI continues to raise the profile of biosecurity issues within its membership through the quarterly LI Biosecurity Newsletter and its biosecurity web page.
‘The landscape profession has directly applicable skills in landscape character assessment and visual impact assessment to identify the significant impact ash dieback is likely to have in the UK,‘ says Roger, ‘and to promote strategies which minimise loss and encourage effective replacement’.
The first signs of Chalara in Britain were found in a nursery in Buckinghamshire in February 2012, and in October of that year Food & Environment Research Agency (FERA) scientists confirmed a small number of cases in Norfolk and Suffolk, some in established woodland which did not appear to have any association with recently supplied nursery stock.
Latest Defra figures show that 1,131 sites including 27 nurseries, 411 recently planted sites and 693 sites in ‘the wider environment’, including established woodland, have been hit by the disease.
The Forestry Commission’s online Chalara Viewer shows England, Scotland and Wales overlain by a grid of 10km squares ('hectads'). Shaded squares show areas where Chalara dieback has been confirmed to be affecting ash trees in the natural environment, while the colour of the square indicates the year the disease was reported.
Just over 21% of grid squares indicate the presence of the disease in England, compared with 12.6% in Scotland, 3.4% in Wales and 16.3% overall.