CONTROLLING GROWTH OF SWEET CHERRY TREES WITH PROHEXADIONE-CALCIUM: ITS EFFECT ON CROPPING AND FRUIT QUALITY

Over three seasons, spray applications (0, 125 or 250 ppm) of Prohexadione-Ca (P-Ca, Apogee^®), a gibberellin biosynthesis inhibitor, were made to 4- to 5-year-old `Lapins’/Mazzard sweet cherry trees at 15, 30 or 55 cm of shoot growth to determine the best combination of rate and time to manage tree vigor. P-Ca reduced terminal extension linearly with increasing rate. The extent of growth control was dependent on the time of application. The best combination of rate and timing was 250 ppm applied at the 30 cm growth stage, resulting in a 25% reduction in total terminal extension. In comparison, applications made at the 15 cm growth stage did not suppress shoot growth. Rather, they sometimes resulted in greater shoot extension due to a faster growth rate later in the summer.
In the season of treatment, P-Ca increased fruit weight and firmness in two of three experiments. It did not affect fruit set, yield, or juice soluble solids and titratable acidity. A slight stimulation of terminal extension growth the following year was observed for those P-Ca treatments (e.g., 250 ppm at the 30 cm stage) that significantly reduced terminal extension in the year of treatment. However, there were no residual effects on most cropping and fruit quality variables. P-Ca had no effect on return flowering.