A Technical Report from The Bartlett Tree Research Laboratories
Growing degree days (GDD) are a measure of accumulated heat units. For a physiological change to occur, such as insect molting or plant flowering, an organism must accumulate enough growing degree days. The number of growing degree days needed for these changes to occur in some insect pests and flowering plants is known and should be utilized in integrated pest management programmes (IPM). Using GDD can improve efficiency of plant health care applications. However, limitations exist for its use and landscape managers should be aware of these to make informed decisions.