Effect of timing of hand thinning on productivity of Moorpark apricots destined for drying

Abstract

Summary. Thinning at full bloom was compared with thinning at 3 stages of fruit development and the effects on size, total soluble solids level (TSS) and yield of apricots are reported. In 2 seasons separate branches of 9-year-old Moorpark apricot trees were hand-thinned to a density of 1 blossom or fruit per 50 mm of fruiting wood. Times of thinning were at full bloom, 5–15 mm size fruit, stone tip hardening and 21 days post stone tip hardening. These treatments were compared with an unthinned control. Experimentation was carried out at Loxton, South Australia. All thinning treatments reduced the yield of fresh fruit. Thinning reduced yield of dried fruit irrespective of timing in the first season but only at the 5–15 mm diameter fruit timing in the second season. Total soluble solids level of the fruit was increased by thinning which tended to improve drying ratio. Compared to the unthinned control all thinning treatments increased the size of fresh fruit. Mean fruit weight and diameter progressively decreased as thinning was delayed from full bloom till stone tip hardening. Thinning at full bloom produced higher yields of 35-mm-grade dried fruit than other treatments. To achieve the greatest benefit from thinning it should be carried out at blossoming.