Integrating Cytolin into a chemical thinning program for red ‘Delicious’ apple

Abstract

Summary. The thinning efficiency of Cytolin and its interaction with the blossom thinner naphthalene acetic acid (NAA) and the post-bloom thinner CyLex (a formulation of 6-benzyladenine) were examined in a trial on Hi-Early red ‘Delicious’ apples in northern Tasmania. Cytolin was applied as either a single or split application at 4 concentrations (25, 40, 55, 70 mg/L). The split application was followed by a low rate of NAA at full bloom or by CyLex as a post-bloom thinner. While the higher concentrations of Cytolin achieved some thinning it was not sufficient. Satisfactory thinning levels, with a corresponding increase in fruit size, were achieved by the addition of either NAA or CyLex to the program. There was no consistent difference in thinning effect or fruit size between the single and split applications of Cytolin. High concentrations of Cytolin followed by NAA resulted in a high proportion of pygmy fruit but there were no pygmy fruit at the lower Cytolin rates. In general, split applications of Cytolin improved fruit typiness better than single applications. Cytolin alone had no effect on seed numbers, whereas addition of either NAA or CyLex to the program reduced seed numbers. Fruit firmness was improved by the CyLex treatments. Return bloom decreased with increasing concentration of Cytolin. Thinning and fruit quality can be improved with the recommended label rate of Cytolin (25 mg/L) applied as a split application (12.5 mg/L applied at king petal stage and 12.5 mg/L 3 days later) followed by 3 mg/L NAA at full bloom or by CyLex as a post-bloom thinner. The improvement in fruit firmness and increase in soluble solids by CyLex compared with NAA may make this combination preferable for long-term storage fruit although further assessment is needed.