Regulation of Growth, Flowering and Fruit Abscission with 2-Chloroethanephosphonic Acid1

Abstract
The new growth regulator 2-chloroethanephosphonic acid (Ethrel)3 was applied to apple and peach branches or young trees at several stages of development from prebloom to harvest. Application at 1000 to 2000 ppm during the prebloom to early postbloom stages on several apple cultivars virtually eliminated all fruit with little or no phytotoxicity. Peach foliage and shoots were more sensitive to the chemical. Vegetative growth was checked and flower bud formation promoted in some cases. From one week after bloom to 4 weeks after bloom, fruit set could be reduced but it was not possible to eliminate the fruit in all cases without phytotoxicity. Application from then until a few weeks before maturity had little effect on abscission. Fruit abscission at maturity was promoted with application of Ethrel.

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