Although Ethylene seems to be the key player in abscission, including fruit abscission, other hormones also play key roles. For example auxin delays fruit abscission by reducing the sensitivity of cells in the abscission zone to ethylene.
Cherry Fruit Abscission - Evidence for Time of Initiation and the Involvement of Ethylene
Vernon A. Wittenbach2 and Martin J. Bukovac. Plant Physiol. 1974 October; 54(4): 494–498.
Ethylene, a Regulator of Young Fruit Abscission
John A. Lipe and Page W. Morgan. Plant Physiology 51:949-953 (1973)
The regulation of sweet cherry fruit abscission by polar auxin transport.
Personal Authors: Blanusa, T., Else, M. A., Atkinson, C. J., Davies, W. J. Plant Growth Regulation, 2005 (Vol. 45) (No. 3) 189-198