Thinning Intensity of Ace Spur Delicious and Idared Apples with Ethephon, Benzyladenine and Their Combination

The thinning potential of ethephon and benzyladenine (BA) sprays alone or in combination as post-bloom thinners of Ace Spur Delicious and ‘Idared’ apples grafted on MM 106 rootstock was examined in two successive seasons (2007 and 2008). The treatments included ethephon sprays of 250 and 500 ppm, BA at 100 and 200 ppm and combinations of both, in addition to unsprayed nonthinned trees. Foliar sprays were applied when the average fruitlet diameter was about 10 mm. Thinning response varied considerably with cultivar, chemical(s) used and year. Ace Spur Delicious was more responsive for chemical thinners. ‘Idared’ was considered difficult to thin. Adequate thinning was achieved without adverse side effects with combinations of ethephon and BA on Ace Spur Delicious’ during the two years. Ethephon when combined with BA caused further increase in fruit weight, improved total soluble solids of both cultivars of apples and increased Ace Spur Delicious’ return bloom in the following spring with no significant influence on the fruit shape, number of seeds and fruit firmness. In absence of BA, ethephon applied at 500 ppm offers reliable fruitlet thinning and increased return bloom of Ace Spur Delicious . No spray injury was observed. BA alone at 200 ppm had no significant influence on % thinning, yield, weight and shape of fruits of both cultivars. However, it increased total soluble solids and decreased seed number of ‘Ace Spur Delicious’ fruits. All thinning treatments did not affect % thinning, fruit weight, yield, fruit shape, seed number, firmness and return bloom of ‘Idared’. Reproducibility of results between years was acceptable