Chemical Thinning ‘Gala’ Apple in the Midwest

Abstract

‘Gala’ trees were treated with various chemical thinnersin eight trials conducted over four years. NAA (naphthalene acetic acid) at 10 ppm applied at 10-12 mm fruit diameter caused reduction in fruit set, but was not consistent in causing a fruit size increase. Carbaryl (1-naphthyl N-methylcarbamate) at 2.5 ml/L applied at 10-12 mm fruit diameter consistently reduced fruit set, increased fruit size and improved return bloom compared to the untreated controls. At petal fall, application of carbaryl failed to thin ‘Gala.’ Accel (1.8% N-(phenylmethyl)-1H-purine-6 amino and 0.18% gibberellic acid) at 50 ppm did not thin ‘Gala’ in three of these trials. Endothal (heptani-2,3-dicarboxylate), an experimental bloom thinner, reduced fruit set with an increasing effect with increasing rates. Of the materials currently available carbaryl, applied at 10-12 mm fruit diameter was the most consistent thinning chemical for ‘Gala’.