Crop loading studies with 'Royal Gala' and 'Braeburn' apples: Effect of time and level of hand thinning

The effects of time and level (fruit number/tree) of hand thinning on fruit size were investigated for 'Royal Gala' and 'Braeburn' apple (Malus domestica (Borkh.)) trees growing on dwarfing rootstocks. Early thinning resulted in larger fruit at harvest in three separate experiments whereas the number of fruit per tree had a significant influence on mean fruit weight in only one experiment. Compared to thinning at full bloom (FB), mean fruit weight of 'Royal Gala' at harvest was reduced by 16% when thinning was delayed by 3-4 weeks after full bloom (WAFB), with a much smaller decrease in weight with further delay. 'Braeburn' gave the opposite pattern, with the greatest loss in mean fruit size at harvest being recorded when thinning was delayed by 8 WAFB. Thinning 4 or 8 WAFB resulted in a 17% decrease in leaf area per tree of 'Royal Gala' compared to thinning at FB, whereas later thinning of 'Braeburn' reduced leaf area per tree by 6% per 4 weeks delay in thinning. Removal of fruit from 'Braeburn' spurs at FB reduced spur leaf size, king Bower receptacle diameter/dry weight, and bourse shoot length on that spur in the year after treatment compared to removal at a later time.