How to Manage Pests
Interactive Tools and Models: Degree-Day Utility
What is DDU?
The Degree-Day Utility (DDU) is a very simple program developed by UC IPM for use on personal
computers. The program works under MS-DOS, on Windows computers.
- The program includes five methods for calculating degree-days.
- The calculations are based on a series of system prompts and user responses.
- Degree-days can be calculated from temperatures in a weather file or from
temperatures you enter from the computer's keyboard.
- Resulting daily or accumulated values can be displayed on the screen or stored in a
- Reference degree-day tables can be created and printed.
- More than fifty phenology models are included in DDU, giving upper and lower
developmental thresholds, degree-day accumulations required for various stages of
development, location of the study, and references. Others are available online.
- Each phenology model can be displayed or printed.
What are degree-days?
A degree-day (oD) is a unit that combines time and temperature, used to estimate the
development of an organism from one point to another in its life cycle. Several methods
are available for calculating degree-days. The user's guide describes degree-day concepts and
methods in detail, and the same info is available online.
Degree-days are a valuable tool in crop management:
- to help growers and consultants to anticipate biological events resulting in better
pest control and crop management decisions
- to minimize conflicts between cultural operations such as irrigating and applying
The DDU software and documentation are now available free online. California
weather data formatted for DDU is also available on this site, under "Degree-days."