Chemical Promotion of Fruit Abscission in Cherries and Plums with Special Reference to 2-chloroethylphosphonic Acid1

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Abstract
Fruit removal force (FRF) of sour cherry, Prunus cerasus L. ‘Montmorency’, was markedly reduced by foliar sprays of 2-chloroethylphosphonic acid (CEPA) applied 3-15 days prior to harvest. The maximum reduction in FRF occurred with CEPA 6 days after treatment for all concentrations (500, 1000, 2000 and 4000 ppm). In addition to a reduction in FRF the dispersion of the individual FRF values was significantly reduced. Fifty per cent fruit removal with the 500 ppm treatment was accomplished by a force of 171 g compared to 434 g for the control. High concentrations (2000 and 4000 ppm) of CEPA caused serious phytotoxicity, such as leaf abscission, terminal dieback, gummosis and enlarged lenticels. Trees of low vigor or the spurs and terminal growth of weak wood were most seriously affected. Fruits on branches treated with CEPA appeared to be advanced in maturity. There was a striking delay in anthesis in the spring following summer application of 4000 ppm CEPA. No significant delay occurred at lower concentrations. Ascorbic acid (20,000 ppm), iodoacetic acid (300 ppm) and salicylic acid (500 ppm) were either not effective or less active than CEPA.

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