USING GROWING DEGREE HOURS ACCUMULATED THIRTY DAYS AFTER BLOOM TO PREDICT PEACH AND NECTARINE HARVEST DATE

The unusually early harvest of California’s peach crop in 2004, which had record high temperatures during bloom time, have increased interest in using earlyspring temperature data to predict harvest date. In the present study an analysis of historical data (2002–2006) for four peach and four nectarine cultivars was used to develop a predictive model for estimating the number of days between full bloom date and harvest date based on growing degree hours accumulated 30 days after bloom (GDH 30). The model can be easily modified for different cultivars by means of using cultivar specific parameters. Our model predicts early harvest in years with warm springs and confirms that heat accumulation following bloom is a major factor affecting fruit development and ultimately, harvest dates. The combination of the model and a web-based decision support tool that calculates GDH 30 values for different weather stations in California allows fruit growers to easily predict harvest dates of numerous cultivars a month after bloom.