Factors Affecting Natural and Ethephon-Induced Grape Berry Abscission

Factors affecting both natural and ethephon-induced grape berry abscission were studied so as to improve the efficiency of mechanical grape harvesting. The natural ease of grape berry removal varied between cultivars and seemed to be related to the ratio of berry weight to berry/pedicel contact area. Within cultivars the ease of berry removal varied with maturity and declined beyond the point of maximum berry weight. Grape berries were shaken off more easily during the cooler hours of the day, perhaps because the berries were then more turgid. The ethylene releasing chemical ethephon aided grape berry removal. The percentage berry recovery increased with increasing ethephon rates. Nonionic surfactants at concentrations up to 0.2% v/v did not improve the response. Ethephon was most effectively applied to the whole vine during the evening. The greatest response occurred about seven days after ethephon application. Grape cultivars vary in their sensitivity to ethephon and require specific rates so as to induce an adequate degree of berry loosening without excessive leaf senescence.