2018 ASHS Annual Conference

Inadequate lateral branch development can have negative consequences on apple orchard productivity and profitability, particularly in high-density orchard systems. While plant growth regulator applications are generally utilized to increase lateral branching on leaders of young apple trees (1^st and 2^nd leaf), inconsistent responses were observed on older trees in the southeastern United States. In 2017, an experiment was initiated to identify effective leader management strategies on 3^rd leaf ‘Gala’/‘M.9’ apple trees at a commercial orchard in Edneyville, NC. Ninety-six uniform trees were selected and treatments were assigned to single-tree plots in a completely randomized design. The experiment had a factorial treatment structure with eight replicates. Effects of leader bagging (bagged or unbagged), 6-benzyladenine (6-BA; applied at green tip, silver tip, or untreated), and 6-BA + GA₄₊₇ (treated or untreated) on lateral branch development of one year-old leaders were evaluated. Leader bagging occurred at the silver tip stage of bud development. Bagged leaders were enclosed in a 96.5 x 15.2 cm section of 4-mil polyethylene tubing and secured using clothespins. Bags were removed once lateral branches were ~ 3 cm long. Where appropriate, 6-BA was applied at 500 mg∙L^-1 and 6-BA + GA₄₊₇ was applied at 250 mg∙L^-1 + 0.2% (v:v) non-ionic surfactant when lateral branches were 3 to 5 cm long. During dormancy, the number and length of lateral branches on the treated section of leader and terminal shoot length was determined. Analysis of variance was used to test main effects and interactions. When compared to unbagged trees, leader bagging increased lateral branch number (17%), average branch length (25%), and total linear bearing surface (43%) of the treated section of leader. 6-BA + GA₄₊₇ increased average branch length (17%), but had no effect on branch number or total linear bearing surface. Measured responses were not influenced by 6-BA or interactions between factors. Terminal shoot length was not influenced by any factor. Leader bagging was effective in increasing lateral branch number, length, and total linear bearing surface, but this procedure was labor intensive. 6-BA did not influence lateral branch number or length at the application timings evaluated, but 6-BA + GA₄₊₇ increased average branch length. Future efforts will focus on productivity and profitability of leader management strategies and characterizing the localized environment of bagged leaders.