The effect of some chemical agents on thinning of Golden Delicious and Granny Smith apples

Abstract

Thinning trials were carried out with various chemical compounds on Golden Delicious and Granny Smith apple trees over a period of three years in the Elgin area in the western Cape. The scorching agents dinoseb (2-sec-butyl-4,-6-dinitrophenol) and paraquat (1,1'-dimethyl-4,4′-bipyridinium ion) caused over-thinning and excessive russeting while ethephon (2-chloroethylphosphonic acid) gave erratic results. Application of 1-naphtylacetic acid (NAA) plus 6-benzyladenine/gibberellins (GA 4/7) as a tank mix on Golden Delicious, 18 days after full bloom, gave the best results with respect to fruit size, production and gross income. Naphtylacetamide (NAD) with and without GA 4/7, resulted in smaller fruit and did not improve yields over the three-year period when compared with a hand-thinned control. A carbaryl (1-naphtyl-N-methylcarbamate) spray on Granny Smith 18 days after bloom resulted in the same fruit size but an increase in gross income of 40% when compared with the hand-thinned control, while trees sprayed with ethephon and NAA did not produce fruit of an acceptable size.