The effect of cyanamide on budbreak and vine development of Thompson Seedless grapevines in the San Joaquin Valley of California

Abstract

Cyanamide (H₂CN₂) was applied to dormant canes on Thompson Seedless grapevines grown in the field to determine its effect on budbreak and subsequent vine development. A 2.5 % (v/v) solution of cyanamide was sprayed on vines just subsequent to pruning in a 2 year study. Vines pruned and treated with cyanamide on January 17 had budbreak 3 and 7 d earlier than the pruned only controls in 1984 and 1985, respectively. The same treatment imposed on March 1 delayed budbreak when compared with the control vines. There were differences of 3 and 6 d between the dates of 50 % bloom for the treatments with the earliest and latest dates of budbreak in both years. The number of degree days > 10 °C between budbreak and bloom averaged 365 and 372 °C · d for all treatments in 1984 and 1985, respectively. There were no significant differences in fruit maturation characteristics such as berry weight and soluble solids concentration among treatments in both years. Results indicate that cyanamide can be used to alter the date of budbreak which subsequently affects bloom date of Thompson Seedless grapevines. However, factors other than those two phenological events become more important in determining fruit maturation of this variety when grown in the San Joaquin Valley of California.