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Growing Degree Days (GDD) and Wheat Growth
Under good conditions wheat plants grow faster in warmer conditions than when its cold. Accumulated GDD is a measure of warmth that has accumulated overtime. For Hard Red Spring Wheat, a GDD is the average of the (daytime high and daytime low) minus 32 degrees. After emergence of the first leaf HRS wheat growth can be accurately predicted by recording temperature. When 143 GDD have accumulated HRS wheat will produce 1 leaf. Each successive leaf also requires 143 GDD. Knowing this, GDD can predict when the crop will be ready to spray with various herbicides. Durum wheat is later maturing than HRS wheat and each leaf require slightly more GDD to fully develop. Barley leaf development requires slightly less GDD than HRS. These growth differences result in more barley development and less durum leaf growth over time compared to HRS wheat depending on variety. GDD, however, provides a practical guide to wheat growth but will need some modifications when applying GDD formula to durum wheat and barley. The NDAWN weather system calculates GDD for wheat http://ndawn.ndsu.nodak.edu/ for many North Dakota locations. Use the date for completions of the first leaf as a base. Subtract this number from current date, divide by 143 to calculate how many additional leaves have developed, add this number to one to arrive at the approximate leaf stage. See W564 http://www.ext.nodak.edu/extpubs/plantsci/weeds/w564w.htm for additional information.
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