|Author: ||S.J. Wertheim|
Abscission of a plant organ occurs when it contains low levels of growth-promoting hormones (auxins, gibberellins, cytokinins) and/or high levels of hormones retarding growth and accelerating ageing (abscisic acid, ethylene). Chemical control of abscission should therefore be based on altering the levels of all hormones involved.
The application of auxins, gibberellins and/or cytokinins has been successful in reducing flower drop (increasing fruit set) as well as immature and mature - fruit drop.
In apple and pear, the most successful chemical control measures available are the use of gibberellins against flower drop (in pear) and the use of auxins to inhibit the pre-harvest drop.
Applications of ethylene, via the ethylene-delivering compound 2-chloroethylphosphonic acid (CEPA), to fruit trees increase the abscission of flowers, of young and mature fruit.
Preliminary work with abscisic acid has shown a promotive effect on apple pre-harvest drop; however, no effect on June drop was found.
Examples are given of several of the control measures mentioned.
The physiological background and some practical aspects are briefly discussed.
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