© Cornell University, 2016. Credits: Tool Developed by Art DeGaetano & Rick Moore.
How do I use this tool?
View our video tool tutorial on YouTube below:
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Instructions on using this tool
Choosing Your Location
- Click the “Change Location” button, which pops up a dialog box with text field and a map (click the small circle button at the top right to exit if needed)
- Create a new location by 1) entering your address, zip code, county, in the text field and clicking the “GO” button, OR 2) clicking on the map at any location in the Northeast
- The “Confirm Location Information” dialog box will appear after clicking “GO,” along with a yellow marker at the new location.
- Click “Save and Select” when you want to see the graph for your chosen location
- Click “Save” when the yellow marker is in the correct location, but you want to add more locations (the color of the new symbol will be changed to blue)
- Click “Cancel” when you do not want to keep the location
Selecting or Deleting Additional Locations
- You may select or delete a location from those already shown (upon clicking “Change Location”) by hovering and then clicking on an existing symbol once the white box with existing location details has appeared
- The “Confirm Location Information” dialog will appear at the top of the map
- Click “Select” when you want to see the graph for that location. When the dialog box closes, the color of the selected location’s marker will be changed to red, and the color of the previously selected marker will be changed to blue. The dialog box will close and your graph will appear
- Click “Delete” to delete the location, immediately removing the marker from the map
- Click “Cancel” when you want to do nothing
Selecting Your Planting Date
- To select a date, click on the small green calendar to display a larger, interactive calendar from which to choose a date by clicking on it, which will automatically update the graph (switch between months by clicking the small arrow in the top left and right of the calendar pop-up box)
Selecting for Growing Degree Day Threshold
- There are two options to select for Growing Degree Day threshold. To select for a Base 50, click on the small circle to left of Base 50. The other option is to select for Base 86/50.
- The graph will automatically update depending on your choice for every parameter.
Choosing Your Season view
- Below the growing degree days there is a group of buttons that allow you to view “Season to Date” or “Season Outlook” charts by clicking on the appropriate button. The “Season to Date” chart contains data for everyday from the beginning of the season until the last forecast date. The “Season Outlook” chart shows the forecast extended to the end of the growing season based on historical accumulations for the remainder of the growing season.
- Each chart shows reference lines to put the current year’s accumulations in context. The most recent 15-year average, the 30-year (1981-2010) average, historical maximum and historical minimum are charted with the selected year’s accumulations.
- The “Info” button provides additional information regarding any methods, models and data used within this tool. References and publications are provided here.
Why is this tool needed?
The Growing Degree Day (GDD) calculator measures heat accumulation to help agricultural producers predict when a crop will reach important developmental stages. It can also be used to help predict potential pest and disease threats. At this time, the GDD tool uses a threshold that was originally optimized for corn production, but it can be suitable for other agronomic crops as well.
How does this tool work?
This tool plots Growing Degree Days (GDD), also called Growing Degree Units (GDUs), which measure heat accumulation in order to predict plant and insect development. In a stress-free environment, the development rate of a plant is dependent on temperature. Using the expected temperature of the summer season, based on previous years, this tool can help predict the best days to plant, harvest, and fertilize.
GDDs are calculated by taking the average of the daily maximum temperature and minimum temperature, and then subtracting a base temperature. The base temperature is the lowest temperature at which a crop will grow. For corn and many other crops, this is 50°F, and is the base that the tool uses. On days when the average temperature is below 50°F, the GDD value is set to zero. Most crops also have a maximum temperature above which growth slows. This temperature is usually approximately 86°F. Thus, the 86/50 degree day method is often used to assess crop development. In this method 86°F refers to the maximum temperature and 50°F the minimum. In computing these degree days, maximum temperatures above 86°F are set to 86 and minimum temperatures below 50°F are set to 50. Typically the 86/50 method is used to assess crop development, particularly corn, while the use of only the 50° base temperature is used to track pest appearance.
Producers can use this tool to:
- Make the best selection of crop varieties, optimize planting and harvesting times, etc…
- Respond to sudden changes: to alter planting plans, seed varieties, etc. if unpredictable weather (i.e. heavy rainfall) occurs
- Assess how a particular season compares to historical or future seasons given climate change.
How is our GDD Calculator different from others?
This calculator uses a moving 15-year average of the most recent 15 years to make predictions, and is updated each year to include the most recent data. Other GDD tools use a fixed 30-year average to make calculations, as opposed to the moving 15-year average, which allows the tool to make predictions that might better align with the changing climate and bring you more up to date information to improve your crop yields.
Please note that this tool only covers the Northeastern United States. If you live outside this region, check out other regional GDD tools:
Unsure of what steps to take next? Click here to find your local Extension office for more detailed advice.