Effect of repeated BA (benzyladenine) application on feathering of 'Idared' apple nursery trees

Since 1993 a serial of trials were carried out concerning improved lateral shoot formation on 'Idared' apple nursery trees. This paper presents the results of trials from 1996 with the aim to find the optimal number of repetitions of BA application. BA was applied in water soluble formulation Paturyl 10 WSC containing 10% of BA. The treatments were applied to one-year-old 'Idared' apple trees budded on 'Malling-Merton 106' rootstock. BA 0.04% was applied 3, 4 and 5 times, each treatment was combined with shoot tip defoliation. BA was sprayed in June weakly to the upper third of 70-80 cm high trees combined with 0.2% Tween 20 detergent. Length and the number and quality of lateral shoots were measured and evaluated at the end of September 1996. BA treatments in 1996 corresponding to the literature and our former results were effective in breaking dormancy of summer buds of one-year-old 'Idared' nursery trees and caused different lateral shoot formation. The number of repetitions of BA application proved to be important, influenced the number and total length of laterals. No influence of different repetition number was found on average length of laterals. Spraying 0.04% BA to Idared trees most effective was the repetition five times but the treatment with four times repetition resulted similar number of laterals and shoot growth. In contradiction to our former results in 1996 shoot tip defoliation combined with 0.04% BA did not affect the lateral shoot growth. Based upon these results 0.04% BA sprays could be recommended repeated five times. BA treatments reduced tree height by 10-15% and the length of internodes in comparison to the untreated trees but the number of internodes did not change significantly. Although this reduction of terminal shoot growth reduced the tree height, the tree size was still great enough to meet standards. While the terminal shoot growth is reduced, the growth of laterals is increased by BA treatments, which means that the total growth of the trees is increased, distributed into terminal growth and growth of laterals. The concurrent growing points of laterals may decrease the terminal shoot growth.