Common ash, Fraxinus excelsior, growing in Ashwellthorpe Wood, Norfolk in September 2013. The brown foliage hanging from the stem in the centre of the picture has died as a result of fungal infection by Hymenoscyphus pseudoalbidus ( also known as Chalara fraxinea ). The affected stem is regrowth from a coppice stool. It will die back to the base.Ash die-back disease was first confirmed in the natural environment in 2012 in the East of England. In May 2013 an occurrence was confirmed in South West Wales. Spread is thought to occur by wind over short distances (up to several kilometres); over longer distances, by the movement of infected tree stock.F. excelsior produces large amounts of seed, which offers an opportunity for the selection of progeny resistant to the disease. However, the fungus also produces sexually, and so may be able to mutate to overcome such resistance.