Uses of 1-aminocyclopropane-1-carboxylic acid (ACC): flower and fruit thinning and flower induction

ACC (1-aminocyclopropane-1-carboxylic acid) is a new product registered in the US in 2022. The principal use is fruit thinning between 15 and 25 mm fruit size.
However, ACC is an ethylene precursor and can be used for other porposes.
The aim of this work was to evaluate of effect of thinning of ACC alone and tank mixed with other products at petal fall time on ‘Gala’ apple.
The second objective was to evaluate the thinning efficacy of ACC at different timings between full bloom and 21 mm of fruit king diameter.
The last objective was to evaluate the effect of ACC, Ethephon and NAA on return bloom.
Our results suggest that among the different combination of products we sprayed during the petal fall (PF) period only the tank mix of ACC and 6-BA showed thinning efficacy.
In the timing experiment, our results suggest that ACC was effective at 11 and 19 mm.
However, the first experiment showed efficacy of ACC at PF, which indicates efficacy between PF and 19 mm.
Weather conditions played a significant role in the efficacy of ACC, with higher thinning efficacy observed during periods of greater tree carbohydrate deficit.
Sprays to improve return bloom of ‘Honeycrisp Premier’ and regular ‘Honeycrisp’, were effective when started around the 16 mm fruit size period and were completed by June 21^st (40 DAFB). Our results suggest that for strongly alternating cultivars such as ‘Honeycrisp’ and ‘Fuji’, it is effective to apply four sprays of Ethephon or ACC at 7-day intervals, starting when the fruits are 16 mm in size.

EUFRIN Fruit Thinning Working Group Symposium

L. Gonzalez Nieto, T.L. Robinson

Malus × domestica, ACC, 1-aminocyclopropane-1-carboxylic acid, Ethephon, NAA, thinning, return bloom, flower initiation and induction

https://doi.org/10.17660/ActaHortic.2025.1443.9