Growth retardant could represent an interesting tool complementary to the
cultural practices to maintain vegetative/reproductive equilibrium. Prohexadione-
Ca, a new bioregulator, showed to be quite effective on pomefruit although little
information is available on the residual effect on apple. The experiment was carried
out in Emilia-Romagna region in 1999 and 2000 on a seven-year-old Fuji/Mark 9
orchard. Prohexadione-Ca was applied as a single or multiple sprays at 125, 175 and
250 ppm; sprays were applied at 5 mm and 20 mm shoot length. Treatments were
repeated for two years on the same trees. Results were compared with untreated
control trees and with treated only in 1999. In both years prohexadione-Ca reduced
shoot length. No residual effect was found in the trees that received the chemical
application only in the first year. As far as the reproductive parameters were
concerned little positive influence was noticed in both years on average fruit weight
although trees sprayed tended to yield more than control. Prohexadione-Ca
positively affected return bloom.
