Historical Chill Hour vs Chill Portions Analysis in the Southeast United States for Better Dormancy Breaking Assessment in Peach

Abstract

The Chill Hour (CH) model has traditionally been used to report and calculate chill requirements (CR) for dormancy breaking in temperate crops like peach and nectarine. However, this model oversimplifies the tree’s response to weather fluctuations and fails to adequately assess CR fulfillment, making it challenging to determine if the reported CH requirement for peach cultivars has been met. The Chill Portions (CP), or Dynamic model, offers a more precise assessment of chill accumulation, especially in warmer regions, and should be used for CR reporting and estimation in tree fruits. There is no simple way of converting CH to CP accumulation for cultivars whose CR is reported in CH without forcing and weather data. To support using CP in CR assessment, we developed a conversion chart between CH and CP for peach cultivars by analyzing CP accumulation for every 50 CH increments over thirty years (1989-2019) using weather data from three different weather stations across the Carolinas and Georgia (KRDU, KGSP, KABY). The implications and need of using the CP model when determining the chilling requirement of future cultivar releases are discussed.