The following resources can help while investigating a shade tree problem. the list of resources is compiled and reviewed every spring in preparation for the Plant and Insect Diagnostic Clinic hands-on workshop "Diagnosing Health Problems of Woody Plants" during the annual Shade tree short course in Ames IA.
ISU Plant & Insect Diagnostic Clinic
Digital photography tips
Iowa DNR Forestry
To find forestry staff and a map of district foresters in Iowa, see https://www.iowadnr.gov/Conservation/Forestry/Forestry-Landowner-Assistance.
IDALS Iowa tree pest information: http://www.iowatreepests.com/
ISU Forestry Tree Identification: http://www.extension.iastate.edu/forestry/iowa_trees/tree_id.html
Recommend shade tree publications
Looking for an Arborist? Trees Are Good is a site with ISA certified Arborist.