Growing Degree Days: Getting Them and How To Use Them
Insects (and mites) are cold blooded organisms and therefore their development rate is directly related to temperature – as temperatures get warmer insects develop faster. In addition, most insects have a lower and upper temperature development threshold, below or above which, respectively, they do not develop. Growing degree days (GDD or DD) are a measure of the “heat units” (related to temperature and the amount of time per day that an insect spends actively growing) that accumulate over time. Therefore, by keeping track of the number of DD that accumulate over time we can predict activity of different insects and their susceptible life stage(s) (target life stage for control measures). For example, when crawler activity of a specific scale insect is likely to occur could be predicted.