Evaluate rest breaking programs for warm winter regions

Rest breaking agents (RBA’s) are applied to alleviate the symptoms of delayed foliation in apple production areas with warm winters where insufficient chilling accumulates. The potential benefits of RBA application include yield increase, greater fruit size (by facilitating thinning), more uniform fruit maturity and the alleviation of delayed foliation symptoms. The objectives of this study were to determine the effect of RBA application on vegetative and reproductive buds, yield and fruit quality.

Individual apple trees of Golden Delicious Reinders, Fuji, and Rosy Glow cultivars planted in commercial orchards in the EGGV regions were selected according to a randomised complete block design and treated with various RBA. The vegetative and reproductive bud break percentages were determined on a weekly basis.

Experiment 1: Applying 3% Dormex® on Golden Delicious Reinders improved bud break. Experiment 2: The 3% Dormex® was too strong a treatment on Fuji in the wet 2013 season. Experiment 3: Treatment with 3% of Dormex® had a fruit thinning effect on Fuji. The 2% LB Urea + 2% KNO3 and 7 days later 0.5% Dormex® + 3% Oil was as an effective rest breaking treatment. Experiment 4: Treatment with 3% Dormex® gave good fruit size and advanced bud break on Golden Delicious Reinders. The 1% Dormex® + 4% Oil was the most effective rest breaking treatment but had a thinning effect. Experiment 5: Treatments were effective in inducing bud break in Fuji, but the effect was not significant. Applying 3% of Dormex® had a negative effect on fruit size. Experiment 6: The bud break progression was poor and not affected by the rest breaking agents in Golden Delicious Reinders. Experiment 7: Applying 0.5% Dormex® + 3% Oil + 100 mg/L Promalin enhanced bud break in Fuji. Experiment 8: Bud break was induced either by 1% Dormex + 4 Oil + 100 mg/L Promalin or 1% Dormex + 4% Oil in Rosy Glow. Experiment 9: Treatment with 3% Dormex® induced more vegetative buds than reproductive buds in Fuji. The return bloom percentage was higher on trees sprayed with 3% Dormex® than on trees sprayed with the other rest breaking agents. Experiment 10: The greatest reproductive bud percentage was with 1% Dormex® + 4% Oil + 100 mg/L Promalin treatment in Rosy Glow apple trees.

The industry recommendation dosage of 3% Dormex® promotes more vegetative buds than reproductive buds on apple trees because of the phytotoxic effect this chemical has on floral tissues. Therefore, spraying 0.5% Dormex® + 3% Oil + 100 mg/l Promalin on ‘Fuji’ apple trees, or 1% Dormex® + 4% Oil + 100 mg/l Promalin on ‘Rosy Glow’ apple trees were preferable as the most promising bud break promoters compared to the other treatments. This research recommends that reducing an expensive dose of 3% Dormex®, to a cheaper dosage of 0.5 – 1% Dormex®, is achievable when incorporated with 3 – 4% Oil and 100 mg/l Promalin on inducing both vegetative and reproductive buds in apple trees