Arboriculture.com currently provides a selection of links related to arboriculture and tree care, particulary in the areas of Integrated Pest Management and Plant Health Care. The site is primarily geared primarily towards arborists and horticulturists, but should also be useful to foresters, landscape architects or anyone interested in trees and shrubs.
- Commercial Services
- Plant Health Care 
- Diseases of Trees
- Insect and Mite Pests of Trees 
- Integrated Pest Management (IPM) 
- Pruning 
Pirone's Tree MaintenanceOrder from Amazon.com for only
I used the sixth edition of this book for the basis of a Maryland Tree Expert certification exam course I developed in the late 90's. I found it to be an excellent introductory text on a number of issues related to tree care; tree selection, planting, soils and pruning. There is also a very good overview of the mirad of tree insects, diseases and other problems, --a topic which might otherwise seem overwhelming in its scope. If you are new to the practice of tree care or looking to prepare for certification, then Pirone's Tree Maintenance is a great place to start.