GDD base 50 = 239. We track GDD at  http://agebb.missouri.edu/weather/reports/gddTable.asp and rate the phenology stages according to the Modified E-L System http://door.uwex.edu/files/2010/10/ModifiedEichhornLorennzsystem.pdf Location Cultivar % primary bud mortality* North Norton 85 – 90% killed primaries Genomics Norton 85 – 90% killed … [Read more...] about Grape phenology and GDD accumulation