This study was carried out for three successive seasons (2006, 2007 and 2008) in a private vineyard located at El-Khatatba, Menoufiya governorate; to determinate the relationship between time of cluster differentiation and phenological stages of vine annual growth cycle with special focus on assessment of bud fertility and bud necrosis sensitivity of eight grape varieties; Flame Seedless, Superior, Beauty Seedless, Black Monukka, Rich Baba, Red Globe, Black Rose, and Ribier. The chosen vines were 10-year-old, grown in a sandy soil, spaced at 2 X 3 meters apart and irrigated by the drip irrigation system, cane-pruned and trellised by the Spanish Parron shape system. The results showed that the time of cluster differentiation is closely correlated closely with phenological stages. However, cluster differentiation occurs just after full bloom time and continues almost until fruit harvest for all varieties in the three seasons of this study. It was noticed that, percentage of dissected bud fertility along ‘Flame Seedless' shoots through the different phenological dates recorded the greatest values compared to the other varieties, followed by Beauty Seedless and Red Globe grape varieties. On the other hand, Black Monukka and Superior grape varieties gave the lowest percentage of dissected bud fertility along shoots through phenological dates in the three seasons of the study. With respect to percentage of bud necrosis, data compiled from bud dissection analysis showed a significant difference in the levels of bud necrosis (BN) among varieties under investigation in the three seasons. In this respect, Flame Seedless and Black Monukka grape varieties had the highest incidence of BN followed by Superior, Beauty Seedless, Red Globe and Black Rose which were found to be intermediate in this respect. On the other hand, Ribier and Rich Baba grape varieties were the lowest during all seasons of this study.