Anticipating crop advancement, particularly fruit maturation, is critical for peach growers' success and marketing. Growing Degree Days (GDD) predict the growth and development stages of plants and insects. They are based on the accumulation of heat units above a specific baseline temperature, under the concept that a certain amount of heat is needed to develop from one stage to another in the life cycle. GDDs are used for various purposes in agriculture and horticulture, such as planting scheduling, pest management and crop monitoring. Peach growers use GDD to predict the peach cultivar maturity and schedule harvesting. However, peach cultivars' ripening time is reported in the calendar or Julian days (JD) or as the number of days before or after a reference cultivar, which is not amenable to climate change. Therefore, we modeled GDD in a diverse set of peach and nectarine cultivars and breeding accessions using the Baskerville-Emin (BE) method. The GDD was calculated from full bloom to fruit maturity using historical temperature, bloom and ripening data collected at the Musser Fruit Research Station in Seneca, South Carolina, in the 2017-2023 period. GDD and JD variability will be presented, and implication of providing GDD information on existing and newly released cultivars for producers and researchers will be discussed.
