Predicting Winter Wheat Heading Date with a Growing Degree Unit Model.

In wheat, maturity is typically categorized as early, medium, or late. However, these designations do not assist growers in determining the approximate date a variety will produce heads in their field, forcing them to scout all of their wheat acreage during a late spring freeze. A heading date model based on growing degree unit (GDU) accumulation was developed to provide growers with a tool to predict wheat maturity. Heading date ratings were taken on 57 varieties replicated five times in Lenoir, Perquimans, and Washington counties in North Carolina, beginning on March 1^st and concluding on April 30^th, 2017. A Julian Date was recorded for each variety on the day it reached 50% heading. The GDU accumulation was calculated using temperature observations from weather stations near each field site. The GDUs were then regressed against the presence or absence of wheat heads at the end of each Julian Day using a logistic regression, which provided a prediction for the number of GDUs that each variety requires to produce 50% of their heads in the field. Based on the model from this year, an early heading variety requires an average of 1831.56 GDUs, a medium heading variety requires 1918.0 GDUs, and a late heading variety requires 1991.5 GDUs to produce a wheat head. On average the predictions were within 54.1, 49.9, and 34.3 GDUs of the actual GDU accumulation in Lenoir, Perquimans, and Washington Counties. The predictions made with this model provide growers with targeted freeze damage warnings for different varieties across the state. Growers can also use this model to make targeted freeze scouting and management decisions based on the maturity of individual wheat varieties.