Thinning of nectarines and peaches is largely an expensive manual task. We investigated the use of organosilicone surfactants as thinning materials that can be applied by mechanized sprayers. Of the surfactants tested, Silwet-408 (Witco) and Boost (Dow-Elanco) were the most effective thinning agents. Spray concentrations of 0.1% or 0.25% (v/v) applied at 30% and 60% full bloom, or 0.5% applied at 80% to 90% bloom, reduced by 50% the mass of fruitlets that had to be hand-thinned and increased the average weight of harvested fruit by up to 20%. When 0.75% to 1% surfactants were applied at 80% to 100% full bloom, fruit yield was reduced by up to 90%. The sprays did not affect fruitlets that had set already, nor did they cause damage to leaves or young shoots. Open flowers were more susceptible to the surfactants than were flowers at tight-bloom or balloon stage. Ion leakage from both petals and flower bases increased in proportion to concentration of surfactant applied, but there was no increase in lipid peroxidation.
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