An espalier apple of about 30 years of age produced a profusion of blossom this year (and last) but now looks dead. There is no recognisable sign of disease, other than all dried up. There has been no drought. Do you know why?
Wilting diseases happen suddenly, like verticillium wilt.
Another apple disease, collar rot, can girdle the tree.
https://www.gardeningknowhow.com/edible/fruits/apples/apple-tree-diseases.htm
https://www.gardeningknowhow.com/plant-problems/disease/verticillium-wilt-treatment.htm