About Growing Degree Days | GreenCast | Syngenta
About Growing Degree Days | GreenCast | Syngenta

Growing Degree Day Model

Growing degree day (GDD) accumulation is commonly used in row crop agriculture to predict important events in plant development such as flowering or crop maturity. In turfgrass management, GDDs are utilized to predict weed seed germination, seedhead emergence, insect pest activity, and plant growth regulator application intervals. When coupled with traditional scouting methods and phenological indicators, GDDs can provide valuable information for turf professionals to maximize the effectiveness of their agronomic programs.

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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" article. 2013.

Growing degree days are calculated by averaging the daily maximum and minimum temperatures and comparing it to a base temperature. This formula subtracts the base temperature from the average daily temperature and calculates the number of heat units for that day or GDDs. When the GDDs are less than zero, it indicates no growth or development occurred on that day. Only GDD’s above zero are accumulated. The base temperature options for this calculator include 32°F, 50°F, 0°C, and 10°C, which should be selected based on the desired growing degree day model or target organism.

Since weather patterns can vary from one geographic area to the next and from year to year, GDDs allow turf management professionals to monitor heat accumulation in their area, which translates to the development of plants and insects. By tracking GDD days, you are able to refine product application timing based on actual weather patterns in your area rather than a predetermined calendar-based schedule.

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When it comes to growing degree day models, it is important to remember that although they serve as useful guides, they don’t replace scouting techniques or your own observations on the course. It is also important to note that for the most accurate GDD data, it’s recommended you utilize an on-site weather station. That said, models such as this do serve as a guide to help you compare month over month and year over year.

If you do have your own weather station, you may see some variances. Reasons include:

  • The location of your weather station and local station feeding this model may be exposed to differences in elevation, proximity to water, shade/sun, and wind.
  • Online model accumulations are reported once a day at midnight each night. Your station will report in real time.