Thinning of Fuji apple. Evaluation of new chemicals versus hand thinning

Mestrado em Engenharia Agronómica - Hortofruticultura e Viticultura - Instituto Superior de Agronomia The chemical agents, ammonium thiosulphate (ATS) (1%), 6-benzyladenine (BA) (100 ppm) and metamitron (100, 175, and 350 ppm) were evaluated as thinning agents on 3 years old „Fuji‟ grafted on to M9 apples trees. The products were used alone, at single or double application or in combination. There were no differences between treatments regarding yield, mean fruit weight and number of commercial fruits (70 – 85 mm) but there were differences concerning the greater and smaller fruit size classes. The fruit set was reduced by metramitron, but when considering different crop loads its action was independent of the crop load for the 175 and 350 ppm concentrations, however, an over thinning effect was observed at 350 ppm in trees with low crop load. Probably, unfavourable weather conditions during the application period of ATS+BA has jeopardized its effectiveness. Hand thinning, leaving one fruit per cluster spaced of 15 cm, was the best option, but is often impossible because of labor costs and the limited supply of available labor