Chemical thinning of apple trees becomes less reliable once fruit exceed 10 mm in diameter. This study evaluated the efficiency of ACC (1-aminocyclopropane-1-carboxylic acid) for late thinning of ‘Fuji Mishima’ in two commercial orchards located at the municipality of Vacaria-RS and São Joaquim-SC, in southern Brazil, during the 2020-21 and 2021-22 growing seasons. Treatments included an untreated control, five different ACC doses applied at either 18-20mm or 25 mm fruit diameter, and a Maxcel® protocol at the 10mm fruit stage. In São Joaquim-SC, ACC at 1.00 and 1.25 kg product ha^-1 applied at 18-20 mm fruit diameter produced the lowest fruit per cluster and a higher proportion large and extra-grade fruit category. At 25 mm of fruit diameter, ACC at 1.25 kg ha^-1 and Maxcel® at 4.5 L ha^-1 were the most effective. InVacaria-RS, ACC at 1.25 kg ha^-1 reduced fruit per cluster at both 18-20mm and 25mm fruitsize. The 0.75 kg ha-1 ACC dose at either fruit diameter increased the proportion of category-3 fruit, as did 1.00 kg ha^-1 applied at 25mm fruit diameter. Overall, ACC at 1.00 - 1.25 kg ha^-1 achieved effective late thinning without detrimental effects on yield or harvested fruit quality. These results indicate that ACC is a viablelate-thinning tool for ‘Fuji Mishima’ under the edaphoclimatic conditions of southern Brazil,during the 2020-21 and 2021-22 growing season.

Managing vegetative vigor is a critical challenge for apple production in subtropical regions, where high water availability often promotes excessive canopy growth. This study evaluated the effects of split applications of prohexadione–calcium (ProCa) combined with naphthaleneacetic acid (NAA) and ethephon on the vegetative growth and yield performance of ‘Maxi Gala’ and ‘Fuji Suprema’ apples during the 2022/23 and 2023/24 growing seasons. The experimental design consisted of six plant growth regulator (PGR) protocols: a commercial standard (Control) with two applications, and five protocols based on six split applications initiated when fruit diameter reached ~8 mm, with 10-day intervals. The treatments included ProCa; ProCa + NAA; ProCa + ethephon; ProCa + NAA + ethephon; and ethephon + NAA. The ProCa + NAA protocol demonstrated the highest efficiency in vigor control, reducing shoot growth by up to 38% in ‘Maxi Gala’ and 65% in ‘Fuji Suprema’ relative to Control. Furthermore, this treatment enhanced fruit skin coloration, increased the proportion of Category 1 fruit, and improved return bloom and overall yield. These findings suggest that split applications of ProCa associated with NAA provide a robust strategy to optimize apple orchard productivity under the edaphoclimatic conditions of southern Brazil.