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Degree Days
Temperature is a key factor contributing to the development of plants,
insects and plant diseases. Degree Days are a way to quantify the
amount of heat that is available, which is a function of the time the tem-
perature is within a given temperature range. For example, if the base
temperature is determined to be 40 degrees and the actual temperature
is 41 degrees for 24 consecutive hours, one Degree Day is said to have
accumulated (41 –
40 = 1
degree for 24 hours or 1 day). Degree Days
indicate the developmental stage of a pest generation. This allows for
more precise pesticide recommendations.
The station
’
s firmware has two options for calculating Degree Days, the
Actual Degree Day Method and the Single Sine Method.
Actual Degree Day Method
Rather than simply using high and low temperature data for an entire
day, the Actual Degree Day Method integrates the data at smaller time
steps. Degree Day subtotals are calculated at 15 minute intervals to
produce Degree Quarter
-
Hours (DQH), which are then summed over a
full day. DQH are calculated as follows:
DQH = T
avg
-
T
base
Where T
avg
is the average temperature over the 15
-
minute interval and
T
base
is the base temperature. If the average temperature is greater than
the upper limit of the temperature range, the upper temperature limit is
used instead of the average temperature when calculating DQH. If the
average temperature is less than the base temperature, DQH is set
equal to zero for that interval
.
Single Sine Method
The Single Sine Method uses the day
’
s maximum and minimum tem-
peratures to generate a sine curve. This approximates the pattern of
temperature variation during a typical day. The area between this curve
and the lower threshold temperature represents the accumulated De-
gree Days for that day.
Chill Hours
Chill hours are calculated as the amount of time spent below a base
temperature. Chill hours accumulations are used to estimate dormancy
for tree fruit.
Degree Days/
Chill Hours
