Growing Degree Days

This information will be updated weekly from March through October to provide current data for use in making pest management decisions. The accumulated Growing Degree Days are 121 from March 1, to March 25, 2020.

About Growing Degree Days (GDD)

The GDD are a measure of heat accumulation used by horticulturists, gardeners, and farmers to predict plant and animal development rates. For example:

  • A crop will reach maturity.
  • An insect will emerge from dormancy
  • The date a flower will bloom

By monitoring the GDD on a daily or weekly basis it is possible to respond accordingly with timely controls.

How It’s Calculated

Calculating GDD is determined by the difference between the daily average air temperature and the base temperature of 50 degrees Fahrenheit (10 degrees Celsius). You must first find the mean temperature for the day. The mean temperature is found by adding together the high and low temperature for the day and dividing by two:

  • Max Temperature plus Minimum Temperature divided by 2 minus Base Temperature equals the Daily GDD

How to Use the Following Table

Using the following table will improve the timing of control measures by helping predict when common pest will appear in Chesterfield County. The table uses the minimum GDD, from past years, to show how it is helpful to monitor pests on a daily or weekly basis in order to predict the appearance and respond accordingly.

Pest Minimum GDD
Eastern Tent Caterpillar 92
Pine Tip Moth 121
Pine Spittlebug 148
Azalea Lace Bug 239
Two-spotted Spider Mite 363
Euonymus Scale 406
Boxwood Leaf Miner 448
Bagworm 600
Fall Webworm
Japanese Beetle