(128) Effect of 2,4-DP Concentration on Fruit Drop Control and Maturation of `Braeburn' Apples

Abstract

Apple fruit abscission shortly before harvest is a frequent, recurring problem, thereby reducing potential yield. The synthetic auxin 2 (2,4-dichlorophenoxy) propionic acid (2,4-DP) was evaluated for its effect on reducing fruit drop and influencing ripening of `Braeburn' apples, in the High Valley region of Río Negro, Argentina (38°56'S, 67°59'W). Thirteen-year-old apple trees grafted on MM 111 rootstock were sprayed on 4 Mar. 2005, at 162 days after full bloom (DAFB) with 2,4-DP at doses of 0.05% and 0.10% (v/v), applied with an airblast sprayer, until runoff. Each tree was trained to palmette and planted in a single row from north to south with spacing of 2.3–4.0 m. The following measurements were performed: a) accumulated fruit drop, twice per week and b) maturity indices, weekly. Samples of uniform-size fruits were assessed for maturity (n = 20 per date and treatment), from 167 (commercial harvest) to 195 DAFB. On 23 Mar. (at 181 DAFB), cumulative fruit drop for control treatment was 19.9%, whereas 2,4-DP significantly reduced it to 4.90% and 2.94% at 0.05% and 0.10% (v/v), respectively. Reduction in the drop was also significant later, and 2,4-DP at both doses controlled drop comparably. The synthetic auxin did not affect fruit quality and maturation, based upon flesh firmness, starch degradation, and soluble solids concentration. We conclude that 2,4-DP is an effective drop control compound and it is useful as a management tool to increase yield by reducing fruit abscission and to extend the harvesting window of `Braeburn' apples, since it does not affect ripening. Delaying harvest may provide flexibility for scheduling of labor, fruit processing and packaging, cold storage, and marketing.