Appendix 2. Calculating Degree Days
The concept of degree days is based on the premise that the higher the temperature, the faster plants and insects grow. Degree days, also called heat units, quantify this relationship.
Degree days are accumulated whenever temperatures exceed a minimum growth (or base) temperature. Base temperature for corn and beans is 50 degrees F. Base temperature for turnips, cabbage and peas is 40 degrees F. Base temperature for peppers is 65 degree s F.
Information on the total degree days required for a crop to reach maturity is often provided by the company selling the seeds. Using this information, the approximate maturity date of the crop can be predicted given the average number of degree days in a particular month for a particular location. Degree days are also used in insect pest management programs to calculate development rates, i.e., how long it will take for eggs to hatch or larvae to mature. Degree days are calculated as shown below.
| Degree days accumulated = [(maximum + minimum daily temperature)/2] - base temperature |
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A typical early corn requires 1,750 degree days, midseason corn 1890 degree days and late corn 1,050 degree days for maturity. Grower with access to maximum and minimum temperatures for their farms could calculate the number of degree days accumulated by the crops to date, subtract this from the total required and estimate the remaining time to harvest based on the past monthly degree-day averages.
Exceptions to this are: