Wednesday, April 2, 2014

Growing Degree Days and Insects

Many people base  the timing of gardening activities such as pest control on the calendar.  Management decisions based solely on a  calendar can prove misleading.  During cool periods plant development may be slower than usual while during warmer periods plant development may accelerate. 

Insects and plants depend upon the temperature to develop. They begin developing when the temperature exceeds a base temperature.  Each development stage of an insect has its own accumulated heat requirement.

Growing Degree Days (GDD) are a measurement of the growth and development of plants and insects and takes into account the average daily temperature accumulations.  GDDs can be used to time control measures for the pests of plants.  Insect pests appear when the GDD reaches a critical value for that particular pest.

The formula for GDD looks something like this:

Max Temp. + Min. Temp.    
2
50 = Daily GDD

50 F is used as the base for these GDDs because this is the temperature at which woody plants in the northeast begin to grow.  For each day that the average temperature is one degree above the base temperature, one degree day accumulates.

GDDs can also be used to predict other events related to the accumulation of warmth such as the blooming of plants.

Predicted Appearance Dates for Various Pests, 2000-2009
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




Additional Information

Growing Degree Days - Cornell University

Using Growing Degree Days for Insect Pest Management

Track Pest Development with Growing Degree Days

What is phenology? - Ohio State University