Extension Ag Update
November/December 2003
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Degree Days Help Predict Crop and Insect Growth

Ellen Phillips, Extension Educator – Crop Systems, Countryside Extension Center, 708-352-0109, ephillps@uiuc.edu

Development of agricultural pests and crop growth can be tracked and projected by maintaining an account of the "heat" accumulated during each day in the growing season. This process involves a comparison of daily maximum and minimum temperatures to a base temperature, specific for a particular pest or crop, above which development will occur. New websites assist growers in quickly calculating this data.

Pest Degree Days: http://www.sws.uiuc.edu/warm/pestdata
Crop Degree Days: http://ipm.uiuc.edu/degreedays/index.html

To use the calculators, begin by selecting the closest of 19 weather stations to your location. Then chose the crop or pest of interest. Degree-day accumulations for some pests have a specific calendar day when accumulations begin, such as January 1 each year. Crop calculations begin later in the year. Accumulations for other pests are tied to specific events; such as pheromone trap catch or finding eggs. Maps of degree-day totals and projections for the entire state are then produced and may be used to assist your scouting efforts.

This webpage is a collaboration combining 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.