Naphthaleneacetic Acid: A Key Tool for Reducing Preharvest Fruit Drop and Sustaining Apple Red Coloration

Abstract

Preharvest fruit drop (PFD) causes significant yield losses in ‘Honeycrisp’ apples. This study evaluated naphthaleneacetic acid (NAA), aminoethoxyvinylglycine (AVG), and their combined application for PFD management, assessing fruit retention and quality for two growing seasons. All treatments generally reduced PFD compared to controls, with AVG, commercially known as “ReTain” (Valent BioSciences LLC), often showing the greatest reduction. However, ReTain consistently impaired red fruit color development. In contrast, NAA, commercially available as “Refine” (Fine Americas, Inc.), effectively controlled PFD without negatively impacting color or firmness, and it improved fruit sweetness. These findings highlight that while both can reduce drop, Refine provides a better balance for ‘Honeycrisp’ growers by mitigating PFD while preserving or enhancing key quality attributes like color and sweetness compared to ReTain.