UK CROWN COPYRIGHT COURTESY OF FERA / SCIENCE PHOTO LIBRARY UK CROWN COPYRIGHT COURTESY OF FERA / SCIENCE PHOTO LIBRARY
Ash dieback disease. This ash tree disease is caused by the fungus Chalara fraxinea, also known as Hymenoscyphus pseudoalbidus in its fruiting stage. It causes necrosis (tissue death) in the tree's stems, causing dieback of the leaves and shoots. Here, the dark brown lesion (top centre, on the cut surface) has occurred after the disease entered through a leaf and worked its way down to the heartwood. The disease can be lethal, especially in young trees. This fungus was first found in the UK in 2012, and it is feared that it may infect millions of ash trees in the UK. Photographed in the UK by the Food and Environment Research Agency.
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