Thinning with NAA, NAD, ethephon, urea and by hand to improve fruit quality of 'Gerdi' apricot

This research was conducted to study the effects of chemical and hand thinning on fruit quality of 'Gerdi' apricot. In the first year, three weeks after full bloom (AFB) branches of mature trees were sprayed with naphthalene acetic acid (NAA) at 10, 20, and 40 mg L-1, naphthalene acetamide (NAD) at 20, 40, and 80 mg L-1, ethephon at 50, 100 and 200 mg L-1, or urea at 0.2, 0.4, and 0.6%. In next year, hand thinning was performed as a separate experiment and leaf to fruit ratio (LFR) was adjusted to 10:1, 20:1 or 30:1 at pit-hardening stage of fruit development. In both years, NAA at 40 mg L-1, NAD at 80 mg L-1 and all concentrations of ethephon significantly increased fruit drop. All concentrations of urea significantly increased fruit drop in 2006, but only the two lower concentrations were effective in 2007. NAA at 20 and 40 mg L-1, and NAD at 40 and 80 mg L-1 increased fruit weight in 2006, but only the highest concentration of NAD was effective in 2007, while urea was effective at all concentrations in both years. Ethephon effect on fruit weight was not significant at all. Hand thinning consistently increased fruit weight, but length and diameter were increased only at a leaf to fruit ratio of 30:1. Hand thinning also increased total soluble solids (TSS), total soluble solids to total acidity ratio (TSS/TA), pit weight and flesh to pit ratio.