Growing degree days calculated with a base of 60 (DD60) have been used almost exclusively by the U.S. cotton industry since the 1980s, and since the initial adoption, DD60s, yield potentials, varieties, and the types and quality of weather data collected have changed drastically. The Extension Cotton Specialists, with the help of a climatologist from North Carolina State University, recently tested the potential of other base temperatures, upper thresholds, and the incorporation of solar radiation to see if slight changes in the calculation might strengthen the predictive power. Results indicated that although the number of required heat units to reach key growth stages has changed slightly, a change in base temperature will likely not increase the predictive power of the calculation. Additionally, an upper threshold may help predictions, but solar radiation will not likely help. Heat units remain a helpful tool for timing certain management decisions based on the maturity of fruiting bodies and comparing weather from season to season.
