Or, E., Department of Tree Breeding, Institute of Horticulture, Volcani Center, Bet Dagan, Israel, Department of Tree Breeding, Institute of Horticulture, Volcani Center, P.O.B. 6, Bet-Dagan 50-250, Israel
Nir, G., Carmel Mizrachi Wineries, Rishon Le'Zion, Israel
Vilozny, I., Department of Tree Breeding, Institute of Horticulture, Volcani Center, Bet Dagan, Israel

One major factor limiting the application of hydrogen cyanamide (H2C2) is the difficulty in deciding when to apply, since mistiming may lead to bud and crop damage. Since an effective method for monitoring the developmental stage of dormant buds is not yet available, minimizing such a risk involves the regional evaluation of application timing. For three successive years, several H2C2 application dates were evaluated in cv. Perlette vineyards in the Jordan valley in Israel. The level and uniformity of bud break did not differ significantly among the application dates tested. However, major effects of the application date on cluster number, cluster size and yield were found. The sensitivity of the reproductive meristem to H2C2 is discussed.