S.A. Bound
The removal of excess or unwanted flowers and/or fruit from trees is one of the most important orchard practices in pome fruit production, ensuring regular cropping and good fruit quality. Increased environmental and public health concerns have led to the banning or phasing out of many thinning chemicals and has encouraged the development and introduction of non-persistent chemicals with low toxicity levels. Many desiccating chemicals have been trialled but most have been unsuccessful because of lack of thinning at low concentrations and phytotoxic side effects at higher concentrations. However, new alternatives show potential. Two trials examined the potential of lime sulphur, fish emulsion, fish oil, potassium bicarbonate and sodium chloride as blossom thinners under Australian conditions. Lime sulphur reduced crop load in ‘Gala’ apples by 40%. Addition of an adjuvant increased the thinning effect up to 80%, depending on the adjuvant. Fruit size and shape were also improved where significant thinning was achieved. A combination of fish emulsion and fish oil reduced crop load by 70%, but fish emulsion combined with Tween 20 had no thinning effect. All fish emulsion treatments resulted in fruit russet. Ecocarb (potassium bicarbonate, Organic Crop Protectants, Australia) resulted in similar thinning levels to ammonium thiosulphate, reducing crop load of ‘Jonagold’ by 50% when applied as a 2% solution with a wetting agent. However a higher concentration of 5% Ecocarb resulted in over-thinning. Sodium chloride applied at either 2 or 5% resulted in over-thinning. Neither Ecocarb nor sodium chloride caused any fruit russeting.
Bound, S.A. (2010). ALTERNATE THINNING CHEMICALS FOR APPLES. Acta Hortic. 884, 229-236
DOI: 10.17660/ActaHortic.2010.884.26
Malus × domestica, blossom thinning, desiccants, lime sulphur, fish emulsion, potassium bicarbonate, sodium chloride

Acta Horticulturae