Effects of Preharvest Applications of Ethephon on Maturity and Quality of Several Apple Cultivars1

Apple trees treated with (2-chloroethyl) phosphonic ethephon applications at 400 ppm, plus 2-(2,4,5-trichlorophenoxypropionic acid (fenoprop) at 10 ppm for abscission control, approx 1 month before optimum maturity exhibited increased fruit coloration. On some cultivars, fruit firmness, soluble solids, acidity, and soluble solids-acid ratio were altered. Ethephon accelerated red color development of ‘Starkrimson Delicious’ apples whether or not the trees had been previously treated with succinic acidb-2,2-dimethylhydrazide (SADH); however, the amount of coloration was greater when both SADH and ethephon were used. Ethephon reduced the titratable acidity of ‘Starkrimson Delicious’ fruit resulting in a greater soluble solids-acid ratio. ‘Golden Delicious’ fruit exhibited a definite yellowing of skin color when treated with ethephon but flesh softening was excessive at higher concn. Ethephon treatments applied without an accompanying abscission control chemical resulted in fruit abscission within 2 to 7 days depending on concn. SADH treatment delayed abscission 2 to 3 days as compared to no SADH treatment, where no abscission control was used. Fenoprop was superior to naphthalene acetic acid (NAA) in reversing the abscission stimulation of ethephon.