Attempts have been made to identify factors that can be easily quantified and serve as early harbingers of ultimate fruit abscission. Ward and Marini (1999) applied a high rate of ethephon plus carbaryl to ‘Golden Delicious’ and ‘Delicious’ apples when fruit size was generally greater than 20 mm. At intervals after application, they rated starch content, cellulose activity and quantified respiration rate, water potential, and growth rate. From this and other studies, they concluded that daily fruit measurement is the only practical method to assess early thinner response. Byers et al. (1991), Greene and Krupa (1999), and Wertheim (1971) have also pointed out the usefulness of measuring fruit growth to assess potential fruit drop after thinner application.
Several investigators have used measurement of fruit growth as the primary determinant for early prediction of thinner response (Greene and Krupa, 1999; Greene et al., 2005a. 2005b; Jankovic et al., 2009; Marini, 1998; McArtney and Obermiller, 2010; Ward and Marini, 1999). The premise on which our predictive model is based is the observation that fruit that are destined to drop will slow and stop growth well in advance of the actual time of abscission. This reduced fruit occurs soon after thinner application and usually well within the window to make another application if needed. The objective of these investigations was to develop an easy-to-use system that could be used by orchardists to assess the effectiveness of previously applied thinner(s). This article chronicles a number of experiments that were done over several years to establish important details necessary for accurate prediction.
LaksoA.N.RobinsonT.L.GreeneD.W.2006Integration of environment, physiology, and fruit abscission via carbon balance modeling—Implications for understanding growth regulator responseActa Hort.727321326
WardD.MariniR.P.1999Growth and development of young apple fruit following applications of ethephon plus carbaryl for thinningHortScience3410571059
WertheimS.J.1971The drop of flowers and fruit in apples with special reference to the June drop of Cox’s Orange and its control with growth regulators. Meded. Landbouweschool Wageningen The Netherlands. 71-17