Promoting return bloom in apple

The initiation of the next year flower buds occurs 2-6 weeks after bloom. Therefore, if the tree is exhausted in producing more fruits and/or vegetative tissues during this period, the initiation of flower buds will be negatively affected, and less return bloom will be obtained. Fruit thinning during this period, either chemically or by hand, helps the tree to direct some of their photoassimilates to the production of the next season’s flower buds. It has also been proven that treatments with some PGRs, particularly NAA and ethephon, after the thinning period ends (~ 6 weeks after bloom), can also promote bud initiation and subsequently return bloom.
Based on the results of many field trials, four bi-weekly sprays of NAA (5 ppm) and ethephon (150 ppm) beginning six weeks after full bloom promote return bloom in apple. These sprays can be added to the cover spray. However, if the tank is mixed with oil or a surfactant, the rates of NAA and ethephon should be reduced by 1/3. These rates should also be adjusted to the tree raw volume. Increasing water amount by 3-4X will enhance the positive effect of these treatments.

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