ēKo Pro Series User’s Manual
Page
103
Doc. # 7430-0710-01 Rev. C
9.2 Degree Days (Heat)
Temperature controls the developmental rate of many organisms. Plants and invertebrate
animals, including insects and nematodes, require a certain amount of heat to develop from one
point in their life cycles to another. This measure of accumulated heat is known as physiological
time. Theoretically, physiological time provides a common reference for the development of
organisms. The amount of heat required to complete a given organism's development does not
vary—the combination of temperature (between thresholds) and time will always be the same.
Physiological time is often expressed and approximated in units called degree-days (°D).
Upper and lower developmental thresholds have been determined for some organisms through
carefully controlled laboratory and field experiments. For example, the lower developmental
threshold is 51°F and the upper developmental threshold is 90°F for the San Jose scale
(
Quadraspidiotus perniciosus
). Thresholds vary with different organisms.
The lower developmental threshold for an organism is the temperature below which development
stops. The lower threshold is determined by the organism's physiology. It is independent of the
method used to calculate degree-days.
The upper developmental threshold is the temperature above which the rate of growth or
development begins to decrease or stop as determined by the cutoff method.
Refer to the UC Davis site for more detailed information and also the upper and lower thresholds
used in the calculation:
(
http://www.ipm.ucdavis.edu/WEATHER/ddconcepts.html)
Configuring the Degree Day Calculation
Configure this calculation similar to chill hours but with the appropriate upper and lower limits.
