The influence of time of flowers' and fruitlets' hand thinning of apple trees 'Sampion' on quantity and quality of yield

A B S T R A C T This study was conducted on apple trees, cv. ‘S ampion’ grafted on M.26 rootstock, planted in a commercial orchard situated in eastern Poland close to Lublin in 1992. During the years 1997-1999 the effect of four hand thinning treatments were compared. These were at the pink bud stage, at the end of flowering stage (two weeks after full bloom), and after the June drop. These were compared to the total yield and internal quality, (dry matter, sugar, soluble solids, and acid content) of the fruit of the control trees, on which thinning practices had not been carried out. Thinning flowers or fruitlets in the two consecutive seasons did not influence the quantity of yield, as compared to that of the control trees. Thinning practices, done during the third season of study, resulted in significantly lower total yield than that of the control trees. The dry matter and soluble solids content in the fruit varied from year to year. The values of these characteristics were at their highest in 1998. Soluble solids and sugar content, in the fruit of thinning treated trees, was at its highest in the last year of the trial. There were no significant influences on the acid content in the fruit from the thinning practices, except in the last season, when thinning carried out after the June drop increased acid content.