Ethephon [(2-chloroethyl) phosphonic acid] at rates of 100 to 1000 ppm caused fruit abscission of apples ( Malus pumila Mill. cv. Cortland and Mutsu) when applied 26 to 44 days after full bloom. Ethephon alone or in combination with SADH (succinic acid 2,2-dimethylhydrazide) caused fruit abscission of ‘Early McIntosh’ when applied 30 days after full bloom. When sprayed shortly after completion of June drop, no abscission occurred. Although no fruit abscission followed the post-June drop treatment, flower bud initiation was increased. SADH appeared to enhance the fruit abscission capabilities of ethephon.
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Lord et al. (1975) studied this question.