Preliminary trials to examine the effects of ethephon as a thinner of ‘Gala’ and ‘Jonagold’ apples

Abstract

Trials in southern Tasmania examined the thinning effects of ethephon on ‘Gala’ and ‘Jonagold’ apples. Untreated controls were compared with ethephon thinning sprays applied at full bloom at 50,100,200,400,800 and 1 600 mg I“1 to both cultivars. Thinning of both cultivars was related to the concentration of the spray and in most cases logistic models were fitted. Thinning effectiveness was largely reflected in increased fruit weight and size. The ‘Gala’ fruit was still not large enough for Australian markets. Ethephon at 200 mg I“1 effectively thinned ‘Jonagold’ and produced the required increases in fruit size and weight. ‘Jonagold’ was overthinned by the high concentrations of ethephon, but this was not reflected in increased fruit weight and size. Ethephon also reduced vegetative growth at the higher concentrations which was considered an advantage. More work is required to establish specific recommendations for either cultivar.