Precision crop load management in apples

P. Francescatto, J. Lordan, T.L. Robinson
Pruning and thinning are the most important management practices used to adjust crop load. The number of fruiting buds left after pruning can greatly influence fruit thinning, fruit quality, tree vigor and return bloom. The main objective of this project was to determine the proper bud load to optimize fruit size and maximize crop value of 'Gala' apple. Trees were pruned to six different bud loads at tight cluster stage in the spring of 2014, 2015, 2016 and 2017. Bud loads were defined as the ratio of flower buds:final desired fruit number tree‑1. The initial desired fruit number for these trees was determined at 130 fruit tree‑1 to achieve 100 count fruit size and 75 t ha‑1. The seven bud loads were 1 bud:1 final fruit tree‑1 or 1.5:1, 2.0:1, 2.5:1, 3.0:1, 3.5:1. After pruning, trees were hand or chemically thinned. At commercial maturity, trees were harvested and fruit number, weight and quality were recorded. When data from all four years were combined irrespective of thinning treatment, a strong and statistically curvilinear relationship was observed between crop value and bud load, although only 6% of the variation was explained by this model. This resulted in a relatively high bud load optimum of 2.0-2.5. Moreover, results indicate that maximum crop value was achieved when fruit size was about 150 g and fruit number tree‑1 was 338 fruits tree‑1 which is double the target fruit number we had assumed before the experiment. When years were studied separately, 2016 gave very different results than the other 3 years with a negative linear relationship between crop value and bud load with the lowest bud load having the highest crop value. This was likely due to the severe drought conditions experienced in that year resulting in very small fruit size.
Francescatto, P., Lordan, J. and Robinson, T.L. (2020). Precision crop load management in apples. Acta Hortic. 1281, 399-406
DOI: 10.17660/ActaHortic.2020.1281.53
bud load, apple pruning, fruit size, yield and fruit quality

Acta Horticulturae