Ash dieback disease, caused by the fungus Hymenoscyphus pseudoalbidus (also known as Chalara fraxinea), first emerged in Poland in 1992. It has since devastated ash populations in northern and Eastern Europe, and in Denmark 90% of ash trees are now infected. Its spread to the Netherlands and Belgium was confirmed in 2010.
In February this year, it was discovered in trees imported from Holland to a nursery in Buckinghamshire and a voluntary ban on the import of ash trees was put in place. In October, however, it was first reported from an established woodland, Lower Wood, Ashwellthorpe in Norfolk.
As a result, on Monday 29th October the Government banned all imports of ash trees. In addition, 100,000 trees have been destroyed on 1,000 sites around the UK in an attempt stop the spread of the disease. An urgent survey is being carried out and outbreaks have been identified at over 80 sites around England and Scotland.
At an emergency Cabinet Office briefing Ian Boyd, chief scientist with the Department for Environment, Food and Rural Affairs, warned that ash dieback could spread across the UK by around 20 miles a year, infecting most of the country’s 80 million ash trees within a decade.
Ash is the third most common broadleaf tree in UK woodlands and about 130,000 hectares of British woods contain predominantly ash trees. They contribute to functional ecosystems by providing rich habitats for insects, birds and other wildlife.
The fungus attacks ash leaves, moving inside the tree and preventing it from taking both nutrients from the earth and sugars from photosynthesis. Infected leaves fall in October and the fungal spores spread from these the following July. Symptoms include dark patches on the leaves, which then spread to twigs and branches where cankers can emerge.
Dr Laura Bellingan, Head of Science Policy at the Society of Biology, says: “This disease is not treatable and so in this case as in many others the only option is prevention. Proper resourcing of surveillance and biosecurity measures are essential to keep ahead of the inevitable spread of diseases and we remain to be convinced that these are given sufficient priority in terms of investment and influence.”
What you can do
In 2013 the British Ecological Society is likely to produce a volume of Ecological Issues on this topic, to synthesise the current knowledge and actions concerning tree health. If you would like to become involved with this please contact firstname.lastname@example.org.
UEA’s Adapt Low Carbon Group have launched a smartphone app to help monitor the spread of disease. The free ‘Ashtag’ app will make it possible for anyone to take a photo of diseased leaves, shoots or bark and send it to plant pathologists to identify whether or not the tree is infected. You can upload digital photos and location details direct to the AshTag website.