Fig. 3.

Cumulative daily growing degree days (GDD) for 2005 (open circle) and 2006 (closed circles) in Rock Springs, PA, for the 2005 and 2006 cropping seasons. Growing degree days were calculated by the following equation: GDD = [(*T*
_{max} + *T*
_{min})/2] – *T*
_{base}, where *T*
_{max} is the maximum daily temperature, *T*
_{min} the minimum daily temperature, and *T*
_{base} is the base temperature (4.4°C) (Nuttonson, 1958).