Growing Degree Days

Growing Degree days (GDD) are heat units used as an index to measure pest development during the growing season. Growing degree days for Christmas tree pests are calculated by taking the average of the maximum and mimimum temperatures, measured in degrees Farenheit, each day, and then subtracting a base of 50 degrees F. from that temperature. All positive numbers that result are added to the previous days' total to get cumulative GDD's. For example:

If your daily maximum temperature is 76 deg. F., and the daily minimum is 44 deg. F., then add 76+44 to get 120. Divide 120 by 2 to get an average of 60, and then subtract the base temperature of 50 to leave 10 GDD's for that day.

At this site we have previously listed cumulative GDD's for the current growing season, for sites in New York State, and selected sites in adjacent states. GDD data was collected and displayed for the period from March 1 through mid-September.

We regret that we will no longer be able to provide GDD updates at this site. If you wish to obtain GDD's for your immediate area, you may calculate them yourself using your local temperature records. To calculate your own GDD's, you need to have a good source of minimum and maximum daily temperatures for your growing area. A good max.-min. thermometer will help you in this endeavor.

In previous years, we have obtained GDD's through the Northeast Regional Climate Center at Cornell University. You may obtain more information about the NRCC by visiting their home page at

* For information about the most current Pest Management Guidelines for Commercial Production and Maintenance of Trees and Shrubs please contact the The Resource Center, Cornell University, PO Box 3884 Ithaca, NY 14852-3884. Telephone: 607-255-2080. Fax: 607-255-9946.

Back to Pest Menu