Growing Degree Days Tool

What are Growing Degree Days, and why are they useful?

Different crops have different ranges of temperatures in which they can grow. If the temperature is above or below that temperature range, crop development will not take place. The same is true for the lifecycles of various insects and plant diseases.

Growing Degree Days (GDD) tell us how much time within a certain period the temperature has been within that range. GDD is strongly linked to plant growth stages, insect life cycles, and disease emergence. This allows us to predict what stage of growth a crop should be at, as well as when to expect the appearance of different pests or diseases. Having this information can help with decision making regarding things like harvest and pesticide/herbicide applications.

How are Growing Degree Days calculated?

The first step in calculating GDD is to find the daily average temperature:

The second step is to find the difference between the daily average temperature and the base temperature for a particular crop, insect, or disease:

Where:

• T_mean is the average daily temperature.
• T_max is the maximum daily temperature.
• T_min is the minimum daily temperature.
• T_base is the base temperature for the particular crop, insect, or disease you are looking at.

The GDD value for each day between the selected start and end date is then added together, giving a cumulative value for the time period.

How do I find the correct base temperature and start date for my crop?

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How do I calculate growing degree days for a particular weather station?

On the map, find your weather station and then click on it. A window opens where you can input the start date, the end date, and Tbase to get the total cumulative GDD on the selected time period.

How do I use the GDD calculator tool?

1. Log into Farm Data Tools (opens in a new tab)
2. Hover over “Other tools” in the tool bar near the top of the screen, then select “Growing Days”.
3. Select your preferred station from the drop-down menu.
4. Fill in your start and end dates, as well as the base temperature for your crop.
5. Click “Calculate GDD”.
6. The total GDD, as well as a graph showing the accumulation by date, will show up on the right.