GDD base 50 accumulation for May 21 = 487 http://agebb.missouri.edu/weather/reports/gddTable.asp Phenology stages according to the Modified E-L System http://door.uwex.edu/files/2010/10/ModifiedEichhornLorennzsystem.pdf Some cultivars have begun flowering. … [Read more...] about Grape phenology and GDD accumulation