toggle menu

Degree Days

The growth and development of plants, insects, and many other invertebrate organisms is largely dependent on temperature. A constant supply of thermal energy is required for the growth and development of these organisms, but if certain thresholds are surpassed, low or high, this development may slow down or stop altogether. This accumulation of thermal energy over time is known as Growing Degree Days (GDD’s) or heat units. GDD’s and other heat unit measurements have been used for determination of planting dates, prediction of harvest dates, and selection of appropriate crop varieties.

Disease Models          
Frost Warning             
Precision Farming      
Decision Support        

While the principle of Growing Degree Days sounds simple, reality is not. It is not sufficient to just add temperatures. Organisms accumulate heat in many different ways, within different ranges and with very different responses to temperature extremes at either end of the scale. It is not enough to just ask how many GDD’s a specific plant needs to accumulate until maturity, or how many Heat Units an insect needs to accumulate until it starts to fly. No, you will also need to ask for the precise algorithm, the computation method used to determine GDD’s for a specific organism. The importance of this cannot be stressed enough, particularly when talking about pest development and protective measures: by applying an inadequate computation method you could be days too late in combating a pathogen!

While these formulas are not excessively complicated, they still require a lot of effort and daily inputs, sometimes of only two values (daily temperature lows and highs), sometimes three (lows and highs and an average), but sometimes even hourly values are required. And given the speed within which plants and pathogens develop, this needs to be done on a daily bases. This is where an ADCON system comes in as a perfect solution!

ADCON's Heat Unit extension, a component of our data visualization software addVANTAGE Pro, includes the most commonly used methods for calculating heat units. Users can create templates based on information found in published models. These templates can include the method of heat unit calculation and thresholds for alarms - crucial for accurate management decisions.

Eleven calculation methods are provided in ADCON's Heat Unit extension, including Averaging, Standard, GDD (Growing Degree-Days), Single Triangle, Double Triangle, Single Sine, Double Sine and Near Real-Time. Simply select from a drop-down menu the method you like, and set it up with the proper starting values, cut-off methods, etc.

The cut-off method is also a key component of a phenological model and is typically indicated in published phenology models. The cut-off method modifies the daily degree-day calculation to more accurately reflect an organism's growth response to high temperatures. Three cut-off methods are included in this extension and can easily be selected from a drop-down menu as shown to the left. They are the Horizontal, Intermediate, and Vertical cut-off methods.

Chilling unit values are used to predict several management factors. Fruit growers are the primary users of chilling hours. Decisions such as varietal selection, pruning, and other management factors related to potential yields can be aided by chilling hour calculations.

ADCON's Heat Unit extension software includes a template that makes creating customized phenological models very easy. Simply select the calculation and cut-off methods from the pull-down menus, enter the threshold and alarm values into the appropriate boxes, and save the new model for future use


Various meteorological sensors
Sensors you need to run plant protection models

Agricultural Risk Management
A short outline of benefits of ADCON systems regarding modern Agricultural Risk Management.

Back to overview