Development of agricultural pests can be tracked and projected by maintaining an account of the "heat" accumulated during each growing season. This process involves a comparison of daily maximum and minimum temperatures to a base temperature, specific for a particular pest, above which development will occur.

The following pages result from a collaborative scientific effort that combines daily weather data collected by the Illinois State Water Survey and pest information furnished by the Department of Crop Sciences to provide daily, up-to-date information about pest development in Illinois. Computer algorithms have been developed for tracking 30 agricultural pests.

Users begin by selecting the closest weather station to their location and the pest of interest. Degree-day accumulations for some pests have a specific calendar day when accumulations begin, such as January 1 each year. Accumulations for other pests are tied to specific, user-input events; such as the first trapping of adult pests, sighting of eggs, etc. One- and two-week degree-day projections are also included. Maps of degree-day totals and projections for the entire state are produced where appropriate.

All degree-day information is computed from data collected through the day just prior to when a user accesses the system. In general, up-to-date information should be available by 4:00 a.m., seven days a week.