The accumulated Growing Degree Days are 4563.5 from October 24, 2016 through October 31, 2016.

This is the last update until March 2017. 

This information will be updated weekly from March through October to provide current data for use in making pest management decisions.  

The concept of GDD presumes that both plant growth and pest development depend on the accumulated amount of heat received during the growing season.  The generally accepted method for calculating GDD is to determine the difference between the daily average temperature (average of the high and low temperature for a given date) and the base temperature, usually 50°F.  For example, if the average temperature on a given day were 65°F, the GDD accumulated for that day would be 15.  Negative values are ignored, for on cooler days, plant growth and insect development do not regress, but simply slow, to speed up again when the weather warms.

 When pest management is based solely on calendar dates, predicting the timing of control measures can be difficult.  It has been determined that a given insect pest appears each year when the accumulated GDD reaches a critical value for that pest.  Along with the current GDD data provided above, this information can be used to predict when a given pest will appear, thus allowing for improved timing of control measures.  The same is true for plant development, e.g., bloom times for many ornamentals correlate well with GDD.

 The following table utilizes the GDD for the years 2000-2009 for some of the common pests encountered in the Chesterfield County area.  The “Minimum GDD” column shows the minimum GDD needed before the pest appears.  As you can see, temperature differences from year to year can shift the appearance of these pests by more than three weeks.  By monitoring the GDD on a daily or weekly basis, it is possible to predict a pest’s appearance and to respond accordingly with timely control.

Predicted Appearance Dates for Various Pests, 2010-2014

Chesterfield County, Virginia

Pest Minimum GDD Average Range
Eastern tent caterpillar 92 March 28 March 13 - April 9
Pine tip moth 121 April 3 March 24 - April12
Pine spittlebug 148 April 6 March 27 - April18
Azalea lace bug 239 April 23 April 2 - April 25
Two-spotted spider mite 363 April 29 April 2 - May 10
Euonymus scale 406 May 2 April 25 - May 12
Boxwood leaf miner 448 May 4 April 28 - May 15
Bagworm 600 May 14 May 9 - May 26
Fall webworm 867 May 31 May 22 - June 8
Japanese beetle 970 June 4 May 25 - June 11

For more information on the use of Growing Degree Days (GDD) contact us