Accumulated Degree Days (ADD)

Definition:

Accumulated degree days, or ADD, are a measurement of thermal units required for growth and development of an arthropod, based on 24 hour periods of time. Accumulated degree hours, or ADH, measure the same heat requirements in hours instead of days.

Because arthropods are cold-blooded, their development is influenced by ambient temperature. Each species requires a specific temperature range for development to occur.

If the temperature is too low or too high, development stops.

The alfalfa weevil, for example, has a minimum, or threshold, temperature of 48° F for development to occur. When the ambient temperature falls below this threshold, development is arrested.

Farmers and gardeners can use accumulated degree days to predict when an insect pest will reach a certain stage in its life cycle. Growers can then monitor for pests at appropriate times, and apply treatments of pesticides at the correct life stage. Forensic entomologists also use accumulated degree days to estimate when insects first colonized a corpse and calculate the post-mortem interval.