Black lesions on pear tree leaves and stem

We have 3 pear trees planted 2010 as 3 yr old trees. This year all three have black spots and lesions concentrated along the central rib of the leaves. Virtually all the leaves are affected. The black areas start out moist and then tend to dry out and the leaf cracks. The worst affected tree also has black areas on the new growth shoots, which look like they are all dying. There are small cracked and peeling areas on the bark of all the trees, nothing oozing from them. We have searched the RHS book on Pests and Diseases but are at a loss to identify. Any help much appreciated as we are brand new to gardening.