Trials were carried out at the experimental farm of the University of Bologna, Italy, on 8-year-old peach (Prunuspersica L. Batsch, ‘Stark Red Gold’ nectarine) trees (seven plants per treatment) grafted on seedling rootstock and trained to a Y shape. Four branches per plant, homogeneous for size and fruit load (3–4 fruit per branch), were selected for the experiments. For each treatment, 28 branches were sprayed with 50 ppm (0.22 mM) or 100 ppm (0.44 mM) MJ, or 50 ppm (0.20 mM) PDJ (Nippon Zeon Co., Tokyo, Japan). Both compounds were applied as an aqueous solution (150 ml per branch), which was prepared by diluting a 5% MJ or PDJ stock solution containing 30% (v/v) surfactant (Rheodor460, Nippon Zeon Co.) and 32.5% (v/v) ethanol, following the manufacturer’s instructions. Control branches only received an aqueous solution containing the same concentration of surfactant and ethanol.