Two years of application of prohexadione-Ca on apple: Effect on vegetative and cropping performance, fruit quality, return bloom and residual effect

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 rum 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.