Evaluation of different methods for the shoot growth regulation of apple trees

Abstract

Growth regulation of apple trees is an important measurement to guarantee a constant yield and good fruit quality. In two different trials at Laimburg Research Centre, few methods of growth regulation were evaluated. With the commercial product Paclot New, the active agent paclobutrazol - well known in the past as the commercial product Cultar - was also evaluated. Despite positive results in the past with paclobutrazol, in these two trials no effect of growth inhibition was observed. Only the treatments with prohexadione-Ca could reduce the shoot growth significantly in comparison with the untreated control. Moreover, the root pruning and treatments with paclobutrazol reduced the fruit size significantly in some years. No residues of paclobutrazol were detected during the trials; only in the leaf and shoots and one single year in the soil residues were found.