Ash die back

Hymenoscyphus fraxineus is a fungus that infects ash trees, often seen in young trees and saplings that begin to lose leaves and die back at the tips. Older trees are also affected although a small amount may survive. Here’s a pic of a sapling with the distinctive diamond shaped lesion on the bark. For more details see https://www.forestresearch.gov.uk/tools-and-resources/fthr/pest-and-disease-resources/ash-dieback-hymenoscyphus-fraxineus/