COMSTOCK/ CORNELL UNIVERSITY PRESS, Quarto, PP.574, A COMPREHENSIVE PICTORIAL SURVEY OF THE DISORDERS OF FOREST AND SHADE TREES AND WOODY ORNAMENTAL PLANTS IN THE UNITED STATES AND CANADA
This is a big, heavy book with perhaps more information than one wants on tree and shrub diseases. However, it is considered by many to be the most comprehensive and does have great photos. It is written like a science manual, so it is not very inviting to the casual gardener.