I agree with the above those texts are a must have. For some one just starting out they can be overwhelming.
Just attended the TCI Expo in Hartford Ct. One of the seminars was Plant Health Care taught by Mike Raupp. We all received a copy of his new book, Managing Insects and Mites on Woody Plants: An IPM Approach. How to quickly identify and research more than 145 different pests. One is also available on diseases, these may be helpful on ID'ing the common key issues found in the landscape.