TEMPERATURE
DEVELOPMENTAL UNITS
There are three methods
that are used to determine temperature development units. Two methods, Degree
Days (DD) and Heat Units (HU), are used to help determine insect development
while the third method, Growing Degree Days (GDD) is used in determining the
stage of plant development. A brief description of each method and how it is
computed is as follows: 1. Degree Days (DD) is used to predict
the development of insects. It assumes there are 12 hours of low temperature
and 12 hours of high temperature in a 24 hour period. The DD is calculated by
adding the low and high temperatures, dividing by 2 and subtracting a base temperature
at which the insect is active.
| DD
= Average temperature - Threshold |
| Ex: Max. Temp.=70;
Min. temp.= 45; Threshold = 50 |
|
| In this example
7.5 degree days have accumulated. |
2. Growing Degree Days
(GDD) is used to predict physiological maturity in hybrids and is a modification
of Degree Days. GDD assumes that some biological activity occurs even if the temperature
is above 50F for part of a day, even if the average temperature is below threshold.
| Ex: Max. temp =
65; Min. temp = 40 Threshold = 50 |
|
GDD also assumes that maximum
biological activity occurs at 86F and plants do not grow faster above this temperature.
| Ex: Max. temp =
90; Min. temp = 70; Threshold = 50 |
|
3. Cosine Curve Method
(CCM) - Heat Units (HU) This method is used to predict
insect development and accounts for the fact that temperatures do not stay the
same throughout the 24 hour period, but follow a curve. A cosine curve is fitted
to yesterday's minimum and today's maximum and the temperature after each hour
is computed. The HU accumulations for a 24 hour period are summed and that gives
the number of HU for the day. Ohio IPM & Survey Program
1991 Kenny Road
Columbus OH 43210
Phone (614) 292-8358
Corn,
Soybean, Wheat, and Alfalfa Field GuideBulletin 827