Effect of prohexadione calcium on vegetative growth, yield and scab development on ‘Sinap Orlovskii’ apple trees

There are many apple orchards in the Russian Federation where trees were trained with volumetric canopies; the vigor of these canopies must be suppressed. Prohexadione calcium (calcium 3-hydroxy-5-oxo-4-propionyl-cyclohex-3-enecarboxylate) was developed to inhibit the gibberellins biosynthesis to reduce vegetative growth. The study was done in the commercial orchard of “Planeta sadov” LLC in Michurinck district of Tambov Region (53°02’11.9 “N 40°29’29.9 “E). This research was aimed to evaluate the influence of prohexadione calcium on the length of one-year shoot growth, yield, and scab development on trees of vigorous apple cultivar ‘Sinap Orlovskii,’ planted 6 x 4 m (418 tr. ha-1). After 1.25 + 1.25 g ha-1 prohexadione calcium double treatment, the length of one-year shoots was 1.96 (2019) and 1.60 (2020) times less than Control 1 (without prohexadione calcium application and hand pruning) and 2,00 times less than in hand pruning treatment. The application of prohexadione calcium inhibited apple tree height and reduced the average height growth rate by 10.7% (2019) and 17.0% (2020). Growth retardant treatments stimulated significant yield increases and improved the commercial value of fruits. The enhance of scab protection improved under the influence of prohexadione calcium treatments. The application of growth retardant increased the alternate bearing index