Evaluation of chemical fruit thinning efficiency using Brevis® (Metamitron) on apple trees (‘Gala’) under Spanish conditions

Thinning is an important technique in apple growing which is used to reduce the number of fruits per plant and achieve commercial fruit size and quality. The objective of this work was to evaluate the efficacy of one and two applications of the chemical thinner Brevis® in Gala apple applied at different fruit sizes and at different intervals between the first and second spray. The trials were conducted over two seasons from 2015 to 2016 in apple orchards of the IRTA experimental agricultural stations of Mas Badia and Lleida (Spain). One or two applications with Brevis® were applied at different fruit sizes (king fruit diameter ranging between 7.5 and 13.5 mm) and at a rate of 1.65 kg/ha for all treatments. Under the trial conditions, a Brevis® thinning effect was observed in all trials with a reduction in crop load, fruit set and number of fruits per tree which varied according to the number of applications. In addition, average fruit weight, color and diameter increased significantly with treatments in which Brevis® reduced the number of fruits per tree. The degree of abscission of Brevis® was highly dependent on night temperature and, for this reason, there was a high degree of variability between trials in terms of efficacy. Our results show that the number of days between applications was not as important a factor for Brevis® efficacy as the difference in night temperature in the days immediately after its application.This study was supported financially by project INIA (Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (Spain)) (RTA2012-00116-00-00) in collaboration with ADAMA-Spain