Growing Degree Days (GDDs)
GDDs are becoming a more popular way to determine when to control insect pests that attack ornamental trees and shrubs.
National Weather Service (NOAA), Climate Prediction Center
National Sustainable Agriculture Information Service - Publication #IP157
Weather Underground
University of New Hampshire Cooperative Extension
Cornell University - Woody Ornamentals Entomology
provide accurate and complete climatological data for the commonwealth of PA
