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Growing Degree Days

  • The Growing Degree Day method (GDD) for estimating when insects will emerge is based on the average daily temperature. It is therefore a more accurate method for timing pest management strategies (spraying pesticides, etc.).
  • GDD is calculated by averaging the daily maximum and minimum temperatures and then subtracting the base temperature as follows: ((maximum temperature + minimum temperature)/2) – base temperature.
  • Insects, like plants and many other organisms, are dependent on temperature to develop. During warm years insects develop faster and become problems sooner. During cooler years development is slowed down. Problems from ornamental plant pests may be noticed weeks later in a cooler year than in a warmer year.
  • The Pest Predictive Calendar is a monitoring tool to assist in predicting when susceptible stages of pest insects are active.
  • Use GDD in combination with the Pest Predictive Calendar (click on link to access) to make timely decisions on implementing management strategies to protect your plants.

          Cumulative GDD   (as of Apr 07, 2024)

          Eastern Henrico                175

          Western Henrico              128

Pest-Predictive Calendar | University of Maryland Extension (