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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 file.
  • 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 a pesticide


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."


Statewide IPM Program, Agriculture and Natural Resources, University of California
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Agriculture and Natural Resources, University of California

Accessibility   /MODELS/DDU/ revised: July 10, 2014. Contact webmaster.