Efficiency of metamitron as postbloom thinner in ‘Red Jonaprince’ and ‘Golden Delicious’

Abstract

The aim of this study was to evaluate the thinning efficacy of metamitron applied either alone (single or double application) or in combination with 6-benzyladenine (BA) or naphthalene acetic acid (NAA) in ‘Red Jonaprince’ and ‘Golden Delicious’ apple trees. The experiment was carried out during the 2014 (third growing season) at the commercial orchard located on mountain Fruska Gora, Serbia. Application of chemical thinners was carried out at two fruit diameter stages (‘Red Jonaprince’ 9-11 and 16-18 mm and ‘Golden Delicious’ 8-10 and 14-16 mm). Number of fruit and yield tree-1, fruit size distribution, parameters of fruit ripeness and return bloom were assessed. In both studied cultivars all metamitron treatments effectively reduced number of fruit tree-1 compared to the control treatment, regardless of fruit diameter stages at the moment of its application. Moreover, application of metamitron when the fruit diameter was 16-18 mm influenced overthinning in ‘Red Jonaprince’, especially when it was combined with BA and NAA. These treatments significantly decreased yield tree-1 compared to the control treatment. All metamitron treatments in both tested cultivars resulted in a significant mean fruit weight increase accompanied with increased share of large fruits in total yield in ‘Golden Delicious’. The metamitron treatments with BA and NAA significantly increased flowering intensity for the next year in both tested cultivars. Similar effect was noticed in ‘Golden Delicious’ when metamitron was applied as alone thinner in the same time. The thinning effect of metamitron treatments on TSS as fruit maturity parameters were only observed in ‘Golden Delicious’.