Aerosol Application of Growth Regulators to Retard Abcission of Apple Fruits

Abstract

12 McIntosh, 6 Macoun and 6 Kendall apple trees, all 8-9 yrs. old and on dwarf or semi-dwarf rootstocks, were pressure and water sprayed weekly with aerosol in the early forenoon or late afternoon from mid-Sept. to mid-Oct. The aerosol contained 0.25% naphthaleneacetic acid, 0.5% lanolin and 94.75% dimethyl ether. Two water sprays contained naphthaleneacetic acid at 10 ppm., plus 0.5% ethyl alcohol in one spray and 0.5% Carbowax 1500 in the other. 13.8 mg. of naphthaleneacetic acid were used per bushel of fruit in the water spray and 34 mg. in the aerosol. All treatments delayed abscission of the fruit in every tree, particularly in the Kendall var. where 87% remained 35 days after commercial harvest as compared with 2% on untreated trees. An aerosol of 2,4-dichlorophenoxyacetic acid gave similar results.