I have included pictures of samples taken from a cotoneaster and a mountain ash tree located in the same yard. From my research my best diagnosis is that it is fireblight that is infecting these plants. However the Mountain Ash does not display the a-typical shepards crook which is often associated with Fireblight? Could someone confirm my diagnosis, and perhaps offer some advice as to how to best deal with this? The Cotoneaster is dying back very quickly and is beyond pruning, I fear the entire hedge will be lost with out some sort of chemical intervention?
Check the roots. Summer drought conditions, extreme winters, planting depth, over fertilizing, these are some reason for foliar damage similar to your pics. Not as likely to be a disease or fungus as it is to be environmental stress. Jim.
