Chemical thinning of ‘Fuji’ apples in Southern Brazil with consideration of economic aspects

Abstract

Experiments were carried out using the apple cultivar ‘Fuji’ and the thinning agents NAA, NAAm, carbaryl and ethephon in single and combined sprays, adding either a non-ionic wetting agent or an emulsifiable mineral oil as an adjuvant. Economic analyses were included to select the most profitable treatments. In most thinning treatments the use of mineral oil as an adjuvant improved thinning intensity and mean fruit weight. Ethephon sprays increased fruit set in the light-crop year 1983/84, but had no thinning effect in the heavy-crop year 1984/85. However, taking into account fruit set in both years as well as potential profit, the best treatments proved to be the single sprays NAAm and NAA, applied at 8 days AFB using mineral oil as an adjuvant, and a combination spray of NAAm at FB plus 8 days followed by a later spray (FB + 21 days) of carbaryl. Both thinning agents were applied at low concentrations and with mineral oil as an adjuvant. All three treatments effectively reduced fruit set in the heavy-crop year to a fruit load density similar to that of hand-thinned trees. From an economic point of view the same treatments were superior to hand thinning when considering both years of observation.