Thinning Peaches with Bloom and Postbloom Applications of 2-Chloroethylphosphonic Acid1

Abstract

Bloom or postbloom sprays of 2-chloroethylphosphonic acid (Ethrel) thinned peaches. Applications at full bloom did not produce consistent thinning in ‘Cardinal’. Postbloom sprays applied approximately at endosperm cytokinesis produced consistent thinning of 3 cultivars. Degree of thinning was related to time of Ethrel application. Most thinning was obtained when Ethrel was applied near the end of Stage I or during Stage II. Ethrel sprays within a month after full bloom caused significant fruit size reduction that persisted 2 months or more after treatment. Ethrel sprays within 50 days of harvest accelerated maturity of several cultivars.

Effect of 3-CPA and Ethephon on Growth and Abscission of the ‘Cardinal’ Peach1

“…4). This effect has been observed previously in peach (5,13,15,17), apple (6) and filbert (10). Secondly, since a long period occurs between treatment and abscission, competition for nutrients may occur between fruits which will eventually abscise and those which will remain.…”

“…Classically, studies of light penetration into deciduous fruit tree canopies have been conducted on clear, cloud-free days to provide a smooth diurnal pattern of external light (3,4,6,7,10,12,14,15,16,18,20). Since many of the studies took place in climates with high percentages of clear days, the light regimes were well chosen; however, in climates such as the Northeastern U.S., cloudiness is a common occurrence during the growing season.…”

“…However 3-CPA is not satisfactory for early cultivars (1,3,4,16). Recently (2-chloroethyl)phosphonic acid (ethe phon), an ethylene releasing agent (6,7,14,15), has been used for peach thinning.…”

Effects of Physical and Environmental Factors on the Release Kinetics of Ethylene from (2-Chloroethyl)phosphonic Acid and (2-Chloroethyl)-methylbis(phenylmethoxy)silane

“…Based on the data presented, it is not surprising that inconsistent responses have often been obtained in field applications of ethylene-releasing compounds where conditions of humidity, light intensity, and temperature are in constant flux (6,7,27). In addition, the fact that target chemistry also affects ethylenerelease kinetics underscores the need to consider this parameter when testing ethylene-releasing compounds in laboratory and field studies.…”

“…As a result, (2-chloroethyl)phosphonic acid applica- the low rate of ethylene release (1). Generally, increasing temperature has been associated with increases in response (14,22,23,27), but at high temperatures (e.g., >34°) the breakdown of the parent material may be too rapid to be effective (18). In comparison, (2-chloroethyl)methylbis(phenylmethoxy)silane applied to leaf tissue has been reported to have a substantially lower activation energy (-43 kJ-mol_1 apparent Ea) (22) and is much more consistent in its rate of ethylene release over a wider range of temperatures.…”