RT Journal Article SR Electronic T1 Performance of a Chill Overlap Model for Predicting BudBreak in Chardonnay Grapevines over a Broad Range of Growing Conditions JF American Journal of Enology and Viticulture JO Am J Enol Vitic. FD American Society for Enology and Viticulture SP ajev.2018.18008 DO 10.5344/ajev.2018.18008 A1 Maria Teresa Prats-LlinĂ s A1 Theodore M. DeJong A1 Katherine S. Jarvis-Shean A1 Joan Girona A1 Jordi Marsal YR 2018 UL http://www.ajevonline.org/content/early/2018/09/20/ajev.2018.18008.abstract AB Predicting phenological stages through modelling has significant implications for planning viticultural practices and for predicting the impact of climate change on phenology. The Chill Overlap Model is based on an exponentially declining curve which integrates the demonstrated compensatory relationship between chill and heat accumulation. It also incorporates recent research-based knowledge of physiological changes during dormancy. The aim of this work was to develop parameters in order to create a Chill Overlap Model for predicting bud break in Vitis vinifera cv. Chardonnay grapevines. We also wanted to determine if using a Chill Overlap Model could be better at predicting bud break than previously developed phenology models. The Chill Overlap Model incorporated the use of the Dynamic chill accumulation model, for quantifying accumulation of chill exposure with a cultivar that has a relatively low chill requirement. Bud break timing determined in the Californian and Spanish wine grape-growing regions, which represent a wide range of climates, was used to establish the parameters for a Chill Overlap Model for Chardonnay. The newly developed Chardonnay Chill Overlap Model did not succeed in predicting bud break any better than previous models, but it did highlight significant differences between the dynamics of chilling in grapevines compared to other species on which a Chill Overlap Model had previously been employed. Further research is needed to account for the environmental and vineyard management factors that influence the timing of bud break in order to improve the model and to better understand factors that influence the completion of dormancy in grapevines.