I overheard some farmers talking about GDDs in the coffee shop the other day. What are those?
GDD is short for growing degree days. GDDs are a way for producers to track the development of crops and pests. We all use calendar days to determine the date, but that system alone isn’t enough to measure crop and insect development.
Different crops have different base temperatures (TBASE), if the temperature does not exceed this base threshold, no growth will occur. Wheat has a base temperature of 40 degrees while sweet corn is 50 degrees.
To calculate the GDDs for corn, you need to find the mean temperature for the day. That will require adding the high and low for the day and dividing by two. If the mean temperature is at or below the base temperature, the GDD value for the day is zero. If the mean temperature is above the TBASE, the GDD value is the mean temp minus the TBASE. So, if the high for the day was 80 degrees and the low was 48 degrees, our mean would be 64 degrees or 14 GDD units above the TBASE.
Warmer days obviously have higher mean temperatures and more GDD units, hence quicker plant growth during the cropping season.
Answered by Jake Ledoux of Cornell Cooperative Extension Jefferson County. Contact him at firstname.lastname@example.org.