Promoting Flower Bud Formation in Honeycrisp—the Time Is Now
Honeycrisp starts flower formation really early in the season and by the time fruits are 30 to 36 mm in diameter, which corresponds to about 45 days after full bloom, buds have already formed flowers for next year.
How do we ensure good return bloom for next year?
First step, we must start with early thinning, which can be achieve with bloom thinning with ATS, followed by petal fall thinning using NAA. Early thinning is critical to reduce the concentration of gibberellins produced by the seeds developing in fruitlet, which will inhibit the formation of flowers for next year.
The second step is to use a PGRs to enhance return bloom. NAA (sold under the name of Fruitone L®; PoMaxaTM; RefineTM) applied at 5-10 ppm (2-4 oz/100 gal) at 5, 7, 9 weeks after bloom is one alternative. A second option is to apply Ethephon (sold under the name of Ethrel; Ethephon 2; Motivate TM) at 200 to 600 ppm at 3, 5, 7, 9 weeks after bloom (½ pint/acre of Ethrel at 3 weeks, followed by 1 pint/acre for the other 3 times). Caution to avoid using ethephon with temperatures >80 ˚F to avoid thinning, especially when spraying at the 15-18mm fruitlet stage which corresponds to ~3 weeks after full bloom.
PGRs can be a great tool to promote return bloom in cultivars with strong alternate bearing. However, the effectiveness of the sprays will depend on the implementation of an appropriate thinning program, as trees with excessive crop load will not respond to return bloom sprays.
This article was posted in Apples and tagged Amaya Atucha, Apples, flower bud promotion, Honeycrisp, PGRs, promoting flower bud formation.