Ash disease

Hymenoscyphus fraxineus

Ash dieback is caused by the fungus Hymenoscyphus fraxineus, which was first scientifically described in 2006 under the name Chalara fraxinea. Chalara fraxinea was later discovered to be the asexual stage of the fungus Hymenoscyphus fraxineus. The fungus causes the leaves of ashes to turn black and wither, and long, dark brown spots to appear on the bark of the branches and trunk. Young trees die within a few years of infection, but old trees survive with disease symptoms. Fruiting bodies of the fungus are formed on the leaves of diseased trees that have fallen from the previous year, the spores of which infect the new leaves and twigs in the spring. Since diseased ash trees have a weakened root system, they are easily blown over by the wind.