Evaluation of timing for spraying Metamitron or NAA plus BA for thinning ‘Brookfield Gala’ apple fruitlets

In Chile, apple chemical thinning uses primarily carbaryl, which is expected to be banned in the future. New thinning chemicals are needed. During the 2013-14 season, two trials were conducted in a 'Brookfield Gala'/Pajam 2 orchard. Metamitron (Goltix Compact(MR) 90% WG, 450 g ai ha-1) or BA (Exilis®, 180 g ai ha-1) plus NAA (NAA 800®, 18 g ai ha-1) were evaluated at different timings beginning at 4 mm up to 28 mm fruit diameter at 3 to 8 day intervals. Control treatments included, one without any spray and a sprayed control that included NAA at full bloom, carbaryl (Carbaryl 85 WP, 1368 g ai ha-1) at petal fall and BA (180 g ai ha-1) plus carbaryl (1368 g ai ha-1) at 12 mm fruit. All sprays were done when no carbohydrate deficit was predicted by Malusim Model (Cornell University). Thinning was evaluated on two branches tree-1, fifty days after full bloom, as fruits per cluster (F/C). All treatments differed from the control (2.3 F/C). Metamitron treatments were more effective when applied between 8 and 16 mm fruit (1.0 F/C). NAA+BA treatments were more effective when applied right after petal fall (4 mm fruit; 1.3 F/C). After removing the effect of crop load, average fruit weight was increased with BA+NAA spray at 4 and 12 mm fruit. All treatments of metamitron were different from the control.