Abstract

During the 1996-97 season, at Colchagua, 6th Region, Chile (34º 38' S lat, 71º06' W long), a thinning trial was conducted on 7 year-old 'Braeburn'/MM106 apple trees to evaluate the thinning effect of naphthalene acetic acid (ANA), 2.5; 5.0 and 7.5 mg L-1 at balloon stage (BR), and carbaryl (active ingredient 60 and 120 g 100 L-1) at petal fall (CP) or ten days after (10 ddCP). Additionally, both products were sprinkled combined, but deferred, as 2.5 or 5.0 ANA at BR, and 60 or 120 carbaryl at CP. A completely randomized design with four replicates per treatment was used. As well, a 3x3 factorial ANOVA at 5% was carried out (0; 60; and 120 carbaryl; 0; 2.5; and 5.0 ANA). After natural fruit fall, the thinning effect was evaluated according to initial charge. All treatments reduced fruit set compared to the control, with the exception of carbaryl 60, 10 ddCP, and ANA 7.5 at BR. No treatment produced over-thinning of the trees. In general, early application of carbaryl at(CP) led to larger size fruit than later application. The ANA treatment which improved fruit size the most was 5.0 ANA at BR. With the combined treatments, the most effective ANA concentration to increase fruit size was 5.0, with no differences due to carbaryl. A good correlation between fruit set and fruit weight was observed (R2 = 0.69), this was not the case between fruit set and return blossoms. Only with carbaryl was there a response of return blooms to the reduction of fruit set.