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Viticulture & Enology

Calculating Degree Day Model

Instructions for Excel file containing Degree Day (Base 50) Model:

  1. Find Mesonet temperature data for your closest weather station (, or your own on-site weather station, to input the daily maximum and daily minimum temperatures (in Fahrenheit) into the corresponding data cells for each calendar day (TEMP MAX and TEMP MIN).
  2. The daily average temperature (TEMP AVG) as well as the daily average temperature minus 50 (AVG-50) and degree day (DD50) calculations will be generated automatically.  Values in Column F (AVG-50) that are negative will result in zeros.
  3. The total accumulated degree days (Column J, TOTAL DD) needs to be adjusted to your data range (i.e., range of dates starting with January 1).  To do this, click on the calculated total degree day cell (J1).  In the function (fx) box, you will see the data range currently selected, shown as “=SUM(G3:G368)”.  Change the second number in the range to include the current date.  For example, if you are calculating accumulated degree days between January 1 and February 15, the selected data range should show as “=SUM(G3:G48)”.
  4. Key insect developmental thresholds (i.e., the number of accumulated degree days) will be discussed in class for various insect pests, especially grape berry moth.
  5. Any questions should be directed to Dr. Eric Rebek,

Download Excel Worksheet