Influence of Light and Spray Coverage on Red Color Development of Ethephon-treated ‘McIntosh’ Apples1

Abstract (2-Chloroethyl)phosphonic acid ethephon at 150 ppm increased red color on shaded ‘McIntosh’ apples although color development was slow. Eleven days after ethephon treatment 64% of the shaded fruit on 10-year-old semi-dwarf trees met the color standards for U.S. Extra Fancy Grade while only 37% met this standard 14 days after application on the large trees. No shaded fruit on the check trees were U.S. Extra Fancy. Increased red color on ‘McIntosh’ fruit occurred when ethephon was applied either to the fruit or the leaves.