Flower thinning of apple cultivar Braeburn using ammonium and potassium thiosulfate: Short communication

Abstract

Ammonium and potassium thiosulfate are used commercially or experimentally as flower thinners because they are considered user, environment and consumer safe. The thinning trials were conducted in 2009 and 2010, on three- and four-year-old Braeburn Mariri Red* trees. The chemicals were applied at 1%, 2% and 3% rates of ammonium and 0.5%, 1% and 1.5% of potassium thiosulfate. Both thinning agents reduced fruit set, but were more efficient in 2009, when applied at 20% full bloom, than in 2010, when they were applied at 80% full bloom. Flower thinning with ammonium and potassium thiosulfate increased the average fruit weight, but the highest chemical rates retarded fruit growth. Ammonium and potassium thiosulfate did not affect fruit shape and firmness, but they increased starch degradation, total soluble solids content and titratable acidity. The treatments increased the percentage of flower buds, except at the highest chemical rates, where leaf damage reduced flower bud formation. Ammonium or potassium thiosulfate application may be recommended as the first step in a chemical thinning program