Early signs can be hard to spot. If you notice early thinning or yellowing of leaves, or the tips of branches dying, especially in a group of ash then it could be a sign of infestation. Other signs include long shoots growing from the trunk, vertical cracks in the trunk, signs of tunnelling under the bark and exit holes. If branches are dying or the leaf canopy is sparse this could be a sign of later stages. Call an arborist at the first signs whilst there is still a chance to save your tree.