Cider Apple Harvest Maturity and Preharvest Drop Can Be Effectively Managed with Aminoethoxyvinylglycine, 1-Naphthaleneacetic Acid, and Ethephon

Certain European high-tannin cider apple ( Malus × domestica Borkh.) cultivars used for commercial production of craft hard cider (fermented apple juice) are known to have severe preharvest fruit drop, as well as asynchronous ripening. A 2-year (2018 and 2019) study at two commercial orchards in Wayne County, NY, USA, examined the effects on drop and ripeness of applying three plant growth regulators—aminoethoxyvinylglycine (AVG), ethephon (ETH), and 1-naphthaleneacetic acid (NAA)—on eight different cider apple cultivars. The treatments included i) untreated control, ii) ETH applied 1 week before harvest (WBH), iii) NAA applied 4 and 2 WBH, iv) NAA at 4 and 2 WBH plus ETH at 1 WBH, v) AVG at 4 and 2 WBH, and vi) AVG at 4 and 2 WBH plus ETH applied 1 WBH. Treatments had significant effects on fruit drop: AVG and NAA treatments significantly reduced drop, while NAA+ETH promoted drop, relative to the control. AVG delayed ripening, while NAA+ETH accelerated ripening. Cultivars that tended to have greater natural preharvest fruit drop had a greater reduction in fruit drop when treated with NAA or AVG. Our research can lead to more precise management of cider apple harvest. For example, NAA alone encouraged ripening while reducing drop, which would be advantageous for over-row machine harvest followed soon thereafter by fruit processing. NAA combined with ETH resulted in advanced ripening, reduced fruit detachment force, and fruit drop largely being condensed into the week leading up to harvest, which may be advantageous for shake-and-sweep mechanical harvest followed by short-term storage. AVG alone delayed ripeness and reduced fruit drop, while increasing flesh firmness and fruit detachment force, making this plant growth regulator (PGR) more suitable for hand harvest and long-term storage before processing.