Effects of Bloom Thinning with Lime Sulfur on Fruit Set, Yield, and Fruit Quality Attributes of ‘RubyS’ Apples

Bloom thinning is an important practice that influences the profitability of the orchard. Hence, we assessed the effect of chemical bloom thinning on thinning efficiency and fruit quality of ‘RubyS’ apples. Lime sulfur was applied as a bloom thinning agent at 1, 1 + 3, and 2 + 4 days after full bloom (DAFB), and non-bloom thinning trees were used as controls. Compared to the control and bloom thinning treatments at 1 DAFB and 2 + 4 DAFB, the application of bloom thinning at 1 + 3 DAFB greatly decreased the number of fruits per cluster in both terminal and lateral flowers. Although the application of bloom thinning at 2 + 4 DAFB decreased the number of fruits per cluster in the terminal flower, it did not affect the number of fruits per cluster in the lateral flower when compared to the control. At harvest, the number of fruits per tree (fruits/ tree) and yield (kg/ tree) was significantly higher in control trees than in bloom-thinned trees. However, fruit quality attributes including fruit weight and size, flesh firmness, soluble solids content, area of red-blushed surface, and a* value in the fruit were significantly improved by bloom thinning at 1 + 3 DAFB. Therefore, this study suggested that applying bloom thinning at 1 + 3 DAFB could serve as an effective thinning treatment to manage crop load in trees and improve the quality of ‘RubyS’ apple fruits.