There are various methods for calculating degree days, such as average, triangulation and sine. One simple method involves using the "lower developmental threshold" or "base temperature" and the "maximum threshold" for a specific insect pest or disease organism. This is called the Daily Averaging Growing Degree Day Method. The base temperature and maximum threshold information can be obtained from your local Cooperative Extension Service, while the minimum and maximum temperatures are obtained from local weather instruments.
= the temperature below which the pest will not
= the temperature above which the pest will not
= the lowest temperature for the 24-hour
= the highest temperature for the 24-hour
For example, let's calculate the number of degree days accumulated on one day for an insect that has a base temperature of 55°F and a maximum threshold of 90°F. A min/max thermometer will show you that the maximum (high) temperature on that day was 86°F and the minimum (low) temperature was 62°F.
To calculate degree days for that day, you would add 86 + 62 = 148, then divide 148 by 2 = 74, then subtract 55 from 74 = 19. You would have 19 Growing Degree Days for that day.