Use of Plant Growth Regulators for Feathering and Flower Suppression of Apple Nursery Trees

The use of highly feathered trees can make high-density apple plantings more profitable through enhanced precocity and increased early yield. Currently, nurseries are asked to provide highly feathered trees with wide branch crotch angles. The use of plant growth regulators (PGRs) can play a key role when it comes to branch induction; however, dose and timing both need to be tested to enhance branching without compromising other tree quality attributes. Over the last 4 years, we have conducted studies of the use of MaxCel (R) (6-benzyladenine) and Promalin (R) (a mixture of 1.8% 6-benzyladenine and 1.8% GA(4+7)) in comparison with Tiberon (TM) SC (cyclanilide) at several nurseries in NY, WA, DE, Ontario (Canada), and Chile. The best results were obtained with four applications of MaxCel (R) or Promalin (R) (400 mg.L-1) beginning when leader growth reached 70 cm above the soil line and reapplied at 10-14 days intervals. Promalin (R) was a slightly less effective branching agent than MaxCel (R). On the other hand, Promalin (R) stimulated leader growth resulting in improved final tree height, whereas MaxCel (R) induced the widest branch angles. Overall, we observed good response and quality ratings with 'Cameo', 'Cripps Pink', 'Enterprise', 'Fuji', 'Ambrosia', 'Crimson Crisp', 'Gingergold', and 'Granny Smith', whereas less quality ratings were observed on 'Ambrosia', 'Cortland', 'Goldrush', 'Honeycrisp', and 'Suncrisp'. Response with 'Gala' varied depending on the temperature range. Multiple sprays of Gibberellins (GA(4+7), or GA(3)) at 250 mg.L-1 applied to nursery trees in the late summer inhibited flower bud development and flowering in the orchard the next year. This reduces the risk of fire blight infection in newly planted trees.