During the "How Pests Pester your Trees" webinar today, I was asked what references I use. I use a lot. Here is a short list. Some of these are for keying out, some would be used for verification of ID. Most of these do not include management recommendations; that's a different list!
Books I use (and I use mostly books for initial ID):
Insects that Feed on Trees and Shrubs. Johnson and Lyon. Cornell University Press: http://www.cornellpress.cornell.edu/book/?GCOI=80140100626460
Diseases of Trees and Shrubs. Sinclair and Lyon. Cornell University Press: http://www.cornellpress.cornell.edu/book/?GCOI=80140100028970
The Common Insects of North America. Swan and Papp, 1972. Harper and Row Pub.
Broadleaved Shrubs and Shade Trees- Problems and Management Options. NRAES: http://www.nraes.org/nra_order.taf?_function=detail&pr_id=183&a...
Landscape Plant Problems. 2000. Byther, R., D.Foss, A. Antonelli, R. Maleike, and V. Bobbitt. Washington State University Cooperative Extension. MISC0194.
Among others…like I said on the webinar, I have a whole shelf of them. Audubon books are also quite handy.
Forestry Images www.forestryimages.org
Bug Guide www.bugguide.net
Cornell Plant Disease Clinic: http://plantclinic.cornell.edu/
Cornell Insect Diagnostic Lab: http://entomology.cornell.edu/cals/entomology/extension/idl/idlfact...
New York Invasive Species: http://nyis.info