Apple trees, eight-year-old ‘Gala’/M.9 and four-year-old ‘Golden Delicious’/M.9 have been thinned with 6-
benzyladenine (BA) 50 ppm, 100 ppm and 200 ppm, with 1-naphthaleneacetic acid (NAA) 5 ppm, 10 ppm
and 20 ppm, and with the tank mix combinations of BA 50 ppm + NAA 5 ppm or BA 20 ppm + NAA 5 ppm,
all at 9-10 mm fruitlet diameter. All applied concentrations of BA and NAA thinned both cultivars
significantly and no significant difference was found between BA or NAA thinning action. No concentration
response on thinning was observed with neither BA nor NAA application. All BA or NAA separate treatments
caused yield of fruit to shift to bigger size class. The only concentration response effect was found on
evaluation of mean fruit weight data on ‘Golden Delicious’. The higher concentration of BA was used, the
higher was the weight of ‘Golden Delicious’ fruit. On the opposite, the higher concentration of NAA was used,
the lower was the weight of ‘Golden Delicious’ fruit (not significantly). When BA and NAA were sprayed on
‘Gala’ or ‘Golden Delicious’ as a tank mix combination, similar effect on thinning or fruit growth occurred
comparing to BA or NAA when sprayed alone. Return bloom was enhanced on all thinned ‘Gala’ trees while
flower formation of ‘Golden Delicious’ was better in the case of BA 200 ppm, NAA 5 ppm, NAA 20 ppm or
tank mix spraying of BA 20 ppm + NAA 5 ppm.
