Sweet chestnut blight. Branch of a sweet chestnut tree (Castanea sativa) that has been infected with the fungus Cryphonectria parasitica, the cause of sweet chestnut blight. The diseased area is bright orange. The fungus attacks the bark, killing the tissue, and causing all of the foliage above the infection site to wilt and die. Infection can be chronic and can eventually be lethal, especially in young trees. This disease was first confirmed in the UK in 2011, but has been known in continental Europe since 1938. In the early 20th century the disease wiped out the American chestnut (Castanea dentata) population of the eastern USA. It is feared that the spread of the disease may affect millions of sweet chestnut trees in the UK's woodlands. Photographed in the UK by the Food and Environment Research Agency.