Chalara dieback of ash is a serious disease of ash trees caused by a fungus called Chalara fraxinea (C. fraxinea). The disease causes leaf loss and crown dieback in affected trees, and it can lead to tree death.
In February 2012 it was found in a consignment of infected trees sent from a nursery in the Netherlands to a nursery in Buckinghamshire, England.
In June 2012 it was found in ash trees planted at a car park in Leicestershire which had been supplied by a nursery in Lincolnshire, and the origins of the disease in this case are being investigated. In July 2012 Food & Environment Research Agency (Fera) confirmed cases in the nursery trade in West and South Yorkshire and Surrey, and by September 2012 it had been reported in a nursery in Cambridgeshire.
It has also been found at four recently planted sites - a Forestry Commission Scotland woodland at Knockmountain, near Kilmacolm, west of Glasgow; the car park in Leicester, a college campus in South Yorkshire, and a property in County Durham.
But the disease has not yet been found in the natural or wider environment in Great Britain, that is, outside nurseries and recent plantings.
C. fraxinea is being treated as a quarantine pest under national emergency measures, and it is important that suspected cases of the disease are reported.
A Pest Risk Assessment (PRA) on C. fraxinea has been published, and a formal consultation on its management has been launched by Fera. Comments may sent to Fera until 26 October 2012. To read the PRA and find out about the consultation, visit the plant pests and diseases consultation pages of the Fera website.