A growing degree day is a measurement tool for tracking the accumulation of heat
units, which are necessary for monitoring the growth and development of plants and
insects1. GDDs increase as the temperature increases throughout the spring
and summer seasons. This calculation allows you to track the growth stages of various
plants & insects based on accumulated heat units over time.
Growing degree days can help to predict annual bluegrass weevil (ABW) activity,
and along with local monitoring can help to time insecticide applications for best results.
A base temperature of 50F should be used to track GDDs beginning on March 1.
Peak adult activity typically occurs when GDD50 is between 80 and 150.
Small larvae are active in the stem from 175 to 300 GDD50, and large larvae become most active outside of the stem once GDD50 exceeds 350.
Growing degree days can also be useful to time re-application of plant growth regulators such as Primo Maxx.
A base temperature of 0C is typically used for cool-season grasses, whereas 10C is used for warm-season grasses.
Growing degree day thresholds vary by grass species, management intensity, and local climatic conditions, so refer to local research for the best recommendation for your area.
1United States Golf Association "Getting a Handle on Nature's Clock"