Growing Degree Days Calculator
Learn More About GDD and Scouting
What are Growing Degree Days (GDD)?
Growing Degree Days (GDD), also called heat units or thermal time, measure accumulated heat above a base temperature. They help us track the development of temperature‐dependent organisms (insects, fungi, crops) based on how much “warmth” has accumulated rather than just calendar days.
How is GDD Calculated?
Basic (Averaging) Method:
GDD = ((Tmax + Tmin) / 2) – Base Temperature
- Use 50°F as the base for many pests (e.g., cereal leaf beetle).
- If the daily result is negative, record GDD = 0.
- Optionally cap Tmax at 86°F for heat‐unit models.
UI Extension Factsheets & IPM Resources
Why It Matters for Crops and Pests
GDD aligns management decisions with actual biological development (egg hatch, flowering, pest feeding) rather than arbitrary calendar dates. By matching GDD of pests—like cereal leaf beetle or corn earworm—with crop stages (flag leaf, tasseling, etc.), you can better time scouting and treatments, reduce unnecessary sprays, and improve overall IPM effectiveness.
